Carbohydrates are classified according to the laboratory techniques used to assess them. ADF includes carbohydrate fractions soluble only in acid, principally the woody material Lignin, Cellulose and mineral ash from the plant cell walls. ADF affects digestibility of forage, the higher the ADF, the less digestible it will be. For hay ADF <35% is reasonable but >45% is poor quality and little nutritional value.
Paired endocrine glands lying close to the kidneys they secrete various hormones including the fight flight hormone Adrenaline (epinephrine), plus Norepinephrine. Together these two are called the Catecholamines and are involved in regulating the cardiovascular system and mobilizing fat and carbohydrate stores for energy. Also, Cortisol which helps regulate blood glucose, Aldosterone involved in kidney function and sex hormones (androgen & oestrogen).
Physical exercise which relies on the use of free oxygen in aerobic energy generating processes. Principally carbohydrates are used as fuel and the intensity is low to moderate, so jogging rather than sprinting. As intensity and speed increase Anaerobic systems come into play which do not rely on the presence of free oxygen for energy production.
These comprise a group of Mycotoxins produced by the mould species of the Aspergillus family. Favouring damp warm conditions these moulds may infest grains such as corn, wheat, barley, rice, sorghum, peanut, sunflower and virtually all grains and seeds as well as poorly cured hay. Acute poisoning (Mouldy Corn Poisoning) in the USA is not usually seen in Australia. The toxins principally affect the liver causing chronic damage resulting in ill thrift, poor appetite, anaemia, depression, reduced growth, and poor immunity. Diagnosis is by laboratory screening of feed samples.
Aggressive, fizzy or anxious behavior may be associated with gut pain or discomfort. Abnormal stereotypic behaviors such as wind sucking, crib biting and weaving have been associated with high starch, low forage diets and EGUS. Large starch meals may result in starch overspill into the hind gut with rapid fermentation and lowering the pH there. Hind gut acidity is thought to be a potential cause of gut pain or discomfort and potentially lead to aggressive or irritable behavior. Lowering starch intake, smaller meals more frequently and increasing forage in the ration may reduce the risk.
There are 21 different Amino Acids which form animal proteins. They can be classified according to whether they must be provided whole in the diet (essential) or can be manufactured in the body (non-essential). A third group may have some capacity for manufacture by the body but may become essential in some circumstances such as rapid growth, stress, or illness. These are termed the conditionally essential amino acids.
Not only building blocks for proteins, amino acids play a variety of essential roles in their own right. Adequate dietary supply of amino acids in the form of protein is critical for maintaining health, growth, and tissue repair.
Angular Limb Deformities (bent legs).
Any deviation of a limb from the straight plane. It can arise from the joint(s) or growth plates in long bones, or in the cuboidal bones of the knee or hock. The most common type is an outward slant of the forelimb from the knee joint (Carpus Valgus) and an inward slant of the pastern from the fetlock, away from the midline (fetlock varus). The effect of nutrition is not proven. Causes are believed to include non-symmetric growth in growth plates, trauma, loose slack joints, excessive exercise, and poor limb conformation. See also “Contracted Tendons”.
Cell metabolism normally produces a group of compounds classed as Reactive Oxygen Species (ROS) including peroxides like hydrogen peroxide, free radicals, and unpaired hydroxyl groups. These highly reactive molecules have the capacity to damage proteins, cell membranes and DNA. The body’s natural defense against this damage employs a range of antioxidant compounds to chemically neutralize the ROS and render them harmless. Vitamins A, C and E exert antioxidant effects along with enzymes such as the Selenium dependent Glutathione Peroxidase, and non-enzyme compounds like Lycopene, Lipoic Acid and Ferritin. Supplementation of dietary antioxidants is common practice, especially the use of Vitamin E for horses in hard work which generates more ROS requiring higher antioxidant capacity. Antioxidants are also widely used as preservatives in horse feeds and supplements such as oils to prevent oxidation and rancidity.
Control is via highly complex neurological and hormonal mechanisms involving signaling from nutrients such as glucose and volatile fatty acids, gut fill, the gut hormone Ghrelin which stimulates hunger, and the hormone Leptin from fat tissue which suppresses appetite. Poor appetite can be an issue for performance horses, especially racehorses. Gastric ulceration EGUS is the first cause to be eliminated as gut pain depresses appetite. The old favorite remedy was Vitamin B12 which may have some merit as it is required to metabolize propionate which is increased by high starch diets. Thiamin B1 requirements are also elevated by hard exercise so B Vitamin supplementation may have some value.
The increase in bodyweight in kilograms per day used as a measure of growth rate in young horses. For example, an ADG for a 6-month-old Thoroughbred foal might be of the order of 0.75kg/Day declining to 0.5 kg/Day at age 12 months. Graphs of bodyweight and ADG may be used to ensure growth rate is appropriate for the age of foals and weanlings. ADG is driven primarily by carbohydrate, and to a lesser extent protein intake.
Also known as Vitamin B7 and sometimes Vitamin H it is part of the water-soluble B Group of vitamins and involved as a component of various enzymes employed in the release of energy from carbohydrates, fats, and protein. It facilitates gene expression and hence cell replication and growth. Biotin is produced naturally by gut microbes in sufficient quantity for normal requirements. It is also present in various feeds, Lucerne and Soya are apparently good sources. Horses with poor hoof horn quality may benefit from supplementation of Biotin, though studies on the rate of hoof growth have been inconclusive. Supplemented Biotin dose rate should be in the range of 3-4mg/100kg bodyweight or 15-20mg/Day for a 500 kg horse fed continuously for at least nine months.
Body Condition.
Assessment of body condition relies primarily on evaluation of the amount of subcutaneous adipose tissue (fat) and is useful for measuring the impact of a nutritional program in individuals. Various scoring systems have been developed to assist evaluation, one of the most popular being the Henneke system dating back to 1983 where a score of 1 indicates extreme emaciation and a score of 9 relates to extremely fat with moderate condition scoring 5. Developed for light breeds like Thoroughbreds and Arabians it may be less accurate for ponies, warmbloods, and draught horses. Other factors such as hair coat length, pregnancy, muscle development, gut fill and evaluator bias may affect scoring but whilst imperfect it remains a useful tool. A rise in score (BCS) over time indicates a positive energy balance with increasing fat accumulation, and declining scores arise when the energy balance is negative and body fat deposits are being utilized as an energy source.
a.k.a. Bone Mineral Density (BMD) is a measurement of the relative proportion of bone mineral versus fibrous tissue matrix in boney tissue. It is an important indicator of skeletal health, strength, and resilience. Methods of measurement include X-Ray, Ultrasound, CT scanning and single photon absorptiometry.
Factors influencing BMD include age and exercise (newborn foals have low BMD at only 17% of adult values whereas yearlings may approach 87% of adult density). Training stimulates re-modelling of bone to strengthen areas under the most stress and generally results in increased BMD. Where training stresses exceed the ability of bone to withstand forces applied, fracture or microfracture may result. The ‘’shin soreness’’ common in young Thoroughbreds undergoing race training is a result of microfractures in the shaft of the cannon bone. As BMD increases during training such damage becomes less likely. Stabling a horse even for a week without access to exercise will significantly reduce BMD even when dietary minerals are plentiful. Dietary mineral intake will influence BMD only when bone is being actively re-modelled, that process being driven primarily by sufficient fast work. Increasing Calcium & Phosphorous intake during training of 2-year-old Thoroughbreds is desirable, along with the use of Omega 3 supplements like flaxseed oil which has been shown to improve the Calcium absorbtion and retention rates.
Caused by a toxin produced by the spore forming anaerobic bacterium Clostridium botulinum which is part of the same family as Clostridium tetani, the causative organism of Tetanus. The bacteria grow in conditions where oxygen is absent such as in rotting vegetation or inside the decaying bodies of small mammals like mice and rabbits. Contamination of hay or other feedstuffs by the bacteria or it’s spores or toxin is the route of poisoning. Poorly ensiled forage or haylage is a possible source as is hay, especially large round bales, contaminated by dead rodents. Often the preformed toxin is consumed but foals may eat the bacterial spores which then develop in their intestine and produce toxin. Botulinum toxin A is the most toxic natural substance known, interfering with nerve impulse transmission, and causing flaccid paralysis.
In horses, signs include weakness, ataxia, difficulty prehending and swallowing food, recumbency with inability to rise, and loss of muscle tone of the jaw, tongue, and tail. Foals may show signs of ‘’Shaker Foal Syndrome” including sudden death, motor paralysis, with inability to suck or stand for more than a brief period. Breathing difficulty, constipation and dilated pupils develop later along with frequent urination, elevated heart rate and fatal respiratory arrest. Samples for testing should include the suspect feed, serum, and intestinal contents. Treatment is by intravenous botulinum antitoxin if available, but prognosis is poor.
Care should be taken with ensiled haylage which has an unpleasant odor like compost or mouldy grass clippings. Haylage should smell sweet and fruity, and any which does not should be discarded. Even a tiny amount of toxin can be lethal from a small area of spoiled feed in a bag or bale. The incidence of Botulism in Australia is rare, perhaps in part because the use of ensiled forage feed is also uncommon here.
Bran.
The type fed to horses is wheat bran, oat bran generally being reserved for human consumption. It is a milling by-product comprising the outer part of the seed coat, which is the first part removed by milling, before the more nutrient rich pollard layer is reached. Bran has an average protein content of about 17% with 24% starch and 7% sugars. Despite its reputation for high fibre, the crude fibre content of bran is quite low at around 10%.
Bran’s big drawback as a feed for horses is its very adverse Calcium: Phosphorous balance. The Phosphorous content is nine times the Calcium, so even a relatively small amount of bran can have a significant negative impact on the overall Ca: P ratio in the diet. When used regularly some additional Calcium should be included to balance the high Phosphorous input. Because of its low fibre content Bran is not actually laxative despite its age- old use for that purpose. It is however highly palatable and enjoyed by horses.
Bran Disease. (Big Head)
Also known as ‘’Millers Disease’’ and ‘’Big Head’’ this condition is a Fibrous Osteodystrophy caused by secondary hyperparathyroidism and is caused by either a deficiency of Calcium or adverse balance between Calcium & Phosphorous.
In classical Bran Disease, millers fed their draught horses on wheat bran because it was cheap and readily available. Bran is very high in phosphorous and very low in calcium, so the diet was calcium deficient. As blood calcium levels fall, the parathyroid gland secretes Parathyroid Hormone which mobilizes bone calcium re-modelling and releases calcium from skeletal stores into the blood to maintain critical blood levels, essential for muscle and nerve function. Slowly the calcium in the skeleton is leached out leaving the fibrous component of bone which proliferates in an effort to shore up the skeletal structure.
The loss of mineral causes bones to soften and pathological fractures may result. Surface bone may flake and tear off where muscles and ligaments attach and pain along with shifting lameness is a feature. Lameness can be subtle and difficult to diagnose. A bunny hopping gait due to hip pain may be noticed along with muscle wastage over the rump especially. The bones of the head, being non weight bearing are sacrificed first and enlarge with fibrous tissue proliferation causing the rounded facial contours and thickened lower jaw typical of Bighead. An old test to confirm the disease was to push an ice pick quite easily through the jawbone. Drooping of the lower lip may be observed, possibly from compression of the nerve supply where it passes through the lower jaw.
Correcting the calcium deficiency will reverse the disease process but may be too late to repair more serious skeletal and joint damage. Supplementation of the diet with ground limestone (Calcium Carbonate) fed at the rate of 60g, and – 120g per day has been found effective. Use of Bran should be restricted care taken to properly compensate the calcium balance of the ration.
Branched Chain Amino Acids (BCAA’s)
These are the amino acids Leucine, Isoleucine and Valine are oxidized by muscle to liberate energy. They are all Essential Amino Acids which means they must be provided in the diet. It has been suggested that supplementing them may improve performance by sparing the use of carbohydrate and glycogen as energy sources, thus reducing lactic acid generation and consequent fatigue. At very low exercise intensity BCAA supplements have been shown to lower blood lactate during and after exercise but at higher intensity no reduction in lactate or improvement in performance were seen.
Provision of supplemental BCAA’s may be of benefit by reducing the catabolism (breakdown) of muscle proteins to liberate them when they are in short supply following exercise. An alternative to BCAA supplements is provision of a group of the six amino acids lost in sweat which may prevent muscle protein breakdown and loss of BCAA’s happening. See Sweat & Amino Acids
These are the remaining materials following fermentation of grains by yeast to digest starch and generate alcohol during the brewing or distilling process. Grains are commonly barley and corn but may include any grain or seed used as a source of starch for commercial alcohol production. Whilst the palatability tends to be quite high due to yeast content and remaining sugars, and the protein level also attractive from a nutrition standpoint, Brewers Grains are potentially dangerous and unsuitable for use as horse feed. The reason is that the product is at high risk of contamination by Mycotoxins such as Aflatoxin and others. Warmth and moisture present during production and subsequent storage are ideal conditions for mycotoxin producing mould growth. These toxins are undetectable without laboratory tests and may be present at dangerous levels without obvious mould in the grains.
One of the two “Macro Minerals” the other being Phosphorous, calcium is the most abundant element in the body and associated with bones and teeth for good reason as both require it for their physical structure and development. It is a critical component of Calcium Hydroxyapatite the mineral compound from which bone is formed around its collagenous fibrous tissue and cartilage matrices. About 99% of total body calcium is found in bone.
Calcium is also an essential mineral for proper function of nerve and muscle cells and for blood clotting. Without it nerves cannot transmit messages and muscles cannot contract and relax normally. Skeletal calcium acts as a reservoir to maintain serum calcium at normal levels and the circulating calcium level is tightly controlled within narrow margins. The hormones Calcitonin and Parathyroid hormone control calcium flows into and out of bone respectively. If serum calcium falls below normal, disturbances such as muscle weakness or tremors soon develop such as may be seen in the hypocalcaemia associated with “Milk Fever”, more common in cattle and dogs than horses.
Calcium is absorbed mainly (60% to 67%) in the small intestine. It needs to be in ionic form as a divalent cation Ca2+ to be absorbed, and as such other divalent cations like copper and zinc may compete for transport into the body. Acid suppressor drugs like Omeprazole may reduce absorbtion. Oxalic acid found in tropical grasses forms an insoluble salt, calcium oxalate, which reduces digestibility and absorbtion, potentially leading to a functional calcium deficiency and ‘’Big Head’’ (see Bran Disease). Phytic Acid found in cereal grains like oats and barley may also form insoluble complexes with calcium and reduce digestibility. The amount of dietary Phosphorous present does not affect calcium absorbtion and any dietary calcium surplus to immediate requirements is only poorly absorbed. Accretions of calcium in the gut can form stones called enteroliths, fortunately rare in Australia. Excess calcium in the body is excreted through the kidney and under certain conditions may also be associated with kidney and bladder stones (urinary calculi).
Organic compounds comprising Carbon. Hydrogen and Oxygen joined by chemical bonds. Carbohydrates are formed by green plants from carbon dioxide and water in the process of photosynthesis. Essential as energy stores they also form part of the DNA molecule. The basic structural unit is that of a simple sugar or monosaccharide like glucose. These may be joined in pairs to form disaccharides such as sucrose, or chains of three to six called oligosaccharides. In polysaccharides the chains may contain up to thousands of simple sugar units. Examples include starch, cellulose and lignin in plants and glycogen, the principal carbohydrate storage compound in animals. Once ingested by the horse, to release the energy in these complex molecules they must first be broken down by enzyme digestion to yield simple sugars, primarily glucose, or by bacteria to yield volatile fatty acids.
Simple sugars have a molecular size small enough to be absorbed intact through the gut wall into the blood. More complex carbohydrates like starch require digestion by enzymes like Amylase in the small intestine to split the large molecule into simple sugars for absorbtion. Larger polysaccharides like cellulose resist enzyme attack and can only be digested by bacterial fermentation in the hind gut. Those yield mainly volatile fatty acids, not glucose as the energy bearing product.
One important aspect of carbohydrate metabolism in horses is the Insulin Response which can cause problems when horses consume high levels of non fibre carbohydrates like starch in their diet.
The term refers to the heart and blood vessels including arteries, arterioles, capillaries, and veins. Unlike humans, disease of the vascular system (blood vessels) is rare in horses. Heart disease is also relatively uncommon though a range of congenital and acquired defects do occur. Assessment of the system is aided by use of Electrocardiography and Ultrasound examination.
aka L-Carnitine. Necessary for the transport of fatty acids across the mitochondrial cell membrane where they can be oxidized to produce energy in the form of ATP. Mitochondria are tiny organelles found inside cells and act as energy factories for the cell. Carnitine supplements have been touted as an aid to improving muscle energy metabolism and thereby performance. Various studies have produced conflicting results. Carnitine supplements increase plasma carnitine concentration but not the concentration in muscle where it exerts its main effect. To date, studies in horses have not confirmed that the availability of Carnitine is limiting on exercise performance. Whilst Carnitine appears safe to use at recommended supplement dosages there is insufficient scientific evidence that is has any useful effect on muscle metabolism, increases energy or reduces post exercise muscle soreness in horses. Not recommended for use.
Cartilage is a tough flexible connective tissue with variable characteristics depending on its structure and use in the body. Structural cartilage forms the larynx and supports the soft tissue of the nose for example, whilst fibrous cartilage forms the intervertebral discs. Bone is formed on a cartilage matrix in the embryo and persists as cartilaginous epiphyseal growth plates in bones from which they grow, the plates being replaced by bone as the horse matures. A specialized form, articular cartilage, caps the end of the long bones in joints, providing a rubbery shock absorber lubricated by synovial fluid. These protective articular cartilage caps are supported by microscopic boney columns. When the bone columns are defective the overlying cartilage may collapse leaving a cavity in the covering cap as part of the disease called Osteochondrosis Dissecans or OCD. Cartilage in joints is also subject to trauma as well as wear and tear and may become thin or degenerate as part of osteoarthritis.
A minor surgical procedure commonly performed on broodmares to prevent aspiration of air and contaminants into the vagina. After repeated pregnancies the abdominal muscles may become stretched and slack. The abdominal contents fall downwards within the abdomen, including the uterus which in turn pulls the vulva forward and down where it is prone to soiling by faecal material and to aspirating air when the horse breathes. This can predispose to uterine infections (metritis) and is a common cause of infertility in older mares.
The solution is to surgically remove a narrow strip of skin from each side of the upper part of the edge of the vulval lips and suture the two exposed raw edges together when they will fuse within a few days. The operation is performed under local anaesthesia and complications are rare. The joined section of the vulva is opened with scissors just prior to foaling.
Catabolism is the part of Metabolism where large complex molecules are broken down into smaller simpler ones. Its opposite is Anabolism where small simple molecules are assembled into large complex ones. Catabolism includes the processes used to release stored energy from carbohydrates, fats, and amino acids. Catabolic processes can go hand in hand with anabolic ones such as when muscle proteins are catabolized to yield their amino acids some of which are later reassembled to make other proteins. Another example is when fat stores are catabolized to yield fatty acids to be used as a source of energy.
The caterpillars of concern to horse owners and especially breeders are the Processionary Caterpillar PC specifically Ochrogaster lunifer which has been identified as the cause of Equine Amnionitis & Foetal Loss EAFL. First observed in Australia in 2004 as an outbreak of abortions in eastern Australia the syndrome bore similarities to abortions caused in Kentucky in 2001 by the Eastern Tent Caterpillar. These PC were identified in large numbers on affected farms.
A remarkable research project by workers at the University of Queensland demonstrated that the abortions and some pre-term birth of sickly foals was related to placentitis caused by the hairs or setae of these hairy caterpillars. As the caterpillars shed their skin several times during development the dried shed skins with hairs attached build up in large numbers in the environment. Following ingestion by a mare these hairs, which carry barbs, may penetrate the gut wall, and migrate around the abdomen, piercing the uterus and placenta. The setae carry gut and environmental bacteria with them infecting the placenta and causing a bacterial placentitis and abortion. Post- mortem sections of aborted placenta have actually shown setae embedded in them. An individual caterpillar can carry over 2 million setae and a tree containing 100 caterpillars can contaminate an area of 4,000 square meters with 25 setae per square meter. Control is by removing caterpillar nests from stud farms, insecticidal spraying, and habitat tree removal.
A complex carbohydrate comprising hundreds to thousands of chemically bonded D-Glucose units it is the principal structural component of the cell walls of plants. Cellulose is one of the main components of Fibre and cannot be digested by enzymes in the gut. Instead, it is digested by microbes housed in the large intestine and yields Volatile Fatty Acids which are absorbed and utilized to produce energy. An example of pure cellulose is cotton wool and it is thought to be the most abundant of all organic compounds.
The gaseous halide element Chlorine when chemically combined with other elements forms a Chloride. In the body the Chloride ion is the most abundant negatively charged Anion Cl– and is normally found combined with positively charged Cations such as Sodium Na+, Potassium K+ and Magnesium Mg+, the so- called Electrolytes. Together these act to maintain correct fluid balance inside and outside cells as well as maintaining blood volume, blood pressure and the pH of body fluids. Chloride is also required for the production of the Hydrochloric Acid secreted into the stomach.
A water- soluble nutrient sometimes regarded as part of the B Group vitamins. Regarded as essential in some animals it can be manufactured from the amino acid Methionine in the liver and as part of the molecule acetylcholine plays a role in transmitting nerve impulses as well as formation oof phospholipid cell membranes. Neither Choline deficiency or signs of excess have ever been described in horses and it may not even be an essential nutrient in the horse. Choline is widely included in manufactured feeds in the form of Choline Hydrochloride. Claims for choline include curing fatty liver, assisting transport of nutrients across cell membranes, keeping mucus membranes moist and assisting horses with recovery from damage to the central nervous system. Unfortunately, there is no credible evidence to support these or any other claims in the horse.
Comprising part of the glycosaminoglycan (GAG) fraction of the compound Aggrecan which together with Hyaluronan, Keratan Sulphate and collagen fibrils combines to make the structure of Articular Cartilage. Almost invariably used in conjunction with Glucosamine it is claimed to reduce the onset and severity of osteoarthritis by inhibiting enzymes which degrade articular cartilage. Sources include cattle tracheal cartilage, shark cartilage and mussels.
There is some evidence from in vitro laboratory studies that Chondroitin Sulphate and Glucosamine protect against cartilage matrix degradation. Studies in live horses have yielded mixed but generally weak results with perceived bias related to the supplement manufacturers financial support of the studies. Questions remain in regard to the bioavailability of oral supplements which may be low, and the subjective evaluation of lameness measured in some studies.
Extensive studies in humans of Chondroitin Sulphate both in conjunction with, and without Glucosamine have been undertaken, involving thousands of patients mainly with knee and hip pain. Meta analysis of numerous studies concluded that when the trials were properly constituted and managed there was no difference in response between these two joint supplements and a placebo. There is insufficient evidence from credible trials in horses to support the use of either Chondroitin Sulphate or Glucosamine for the treatment or prevention of joint disease.
A trace element purported to improve insulin sensitivity it is sold as Chromium Picolinate, Chromium Propionate and chelated in Chromium yeast. Some studies in humans indicated positive response to chromium supplementation with improved glucose tolerance in insulin resistant patients. Limited trials in horses yielded conflicting results with slightly lowered peak insulin response to an oral starch challenge test in one experiment, and no significant effect in another larger longer trial. Further research is needed to determine whether or not Chromium has value in the management of Insulin Resistance or potentially Laminitis n horses. Chromium deficiency has never been recorded in horses indicating that normal dietary intake is likely sufficient. Meanwhile Chromium is heavily promoted as enhancing athletic performance, improving health and reducing insulin resistance with scant if any justification.
An essential trace element essential for the formation of Vitamin B12 (Cobalamin) which is manufactured by microbial activity in the hind gut of horses. Essential with Vitamin B12, copper and iron for the formation of red blood cells. Also involved in energy metabolism in complexes with other compounds including production of glucose from volatile fatty acids. Cobalt is absorbed in the hind gut as part of cobalamin complexes formed by gut microbes. Where dietary cobalt is deficient the symptoms would be those of Vitamin B12 deficiency. An intake of 0.5 – 0.6mg per day for a 500kg horse is deemed adequate. Cobalt was tried as a performance enhancer following suggestions in lay press that high doses may stimulate erythropoietin (EPO) production and it was used in competitive cycling and then by some horse trainers in 2013. Racing authorities intervened and set pre- or post- race urine levels of 100 micrograms per liter above which the Rules of Racing may be breached. There has been some controversy over what constitute the ‘’normal’’ range of cobalt in the horse population as it can come from a variety of legitimate natural sources. Appropriate care should be taken if using Cobalt containing feeds or supplements in competitive sport / racehorses.
Colic
Colic means a pain in the belly. It is a symptom, not a diagnosis. Causes are many and varied and colic ranges from mild and transient to severe and fatal so it should always be treated seriously. Most but not all colic’s are related to poor feed management. A sample of different types is listed below:
Gas – most commonly resulting from fermentation of carbohydrates in the large intestine (hind gut) by gas producing bacteria. The carbs can be starch from concentrate feeds like grains, or sugars including fructans in pasture or hay. Gaseous distension of the bowel causes stretching of the wall and pain. Complications locally can include gut stasis and displacement of parts of the bowel with subsequent compromise to the blood supply. Toxins from leaky bowel wall can enter the circulation and precipitate an attack of laminitis.
Obstruction – Can be a physical obstruction by e.g., sand or an accumulation of indigestible fibrous food such as poor- quality hay or straw bedding, or subsequent to a disturbance to the normal motility of the gut with displacement, folding or twisting of a section of bowel. In foals, a specific obstructive colic can be caused by intussusception when a length of gut sleeves in on itself compromising its blood supply and choking off the flow of ingesta. Hernias both internal inside the abdomen, and through the abdominal wall can also obstruct lengths of gut. Enteroliths are accretions of calcium salts forming stones in the gut which may occasionally cause obstruction.
Displacement – often subsequent to gas or a disturbance in normal motility, a length of bowel, either small or large intestine moves or floats to an abnormal position causing twisting of the supporting connective tissue (mesentery) and again, occlusion of blood supply. Requires surgery to correct.
Toxins – a variety of toxins from sources such as poisonous plants, mycotoxins from mouldy feed, contaminants such as heavy metals like lead and certain chemicals such as pesticides can be ingested and result in abdominal pain as one of the symptoms of poisoning.
Spasmodic – A symptom rather than a cause as the name implies spasm of intestinal smooth muscle comes intermittently in waves associated with pain of varying intensity.
Causes are too numerous to cover in detail here. Abrupt changes in feed predispose to colic as does stabling and lack of access to pasture. High grain low forage diets are strongly correlated with higher incidence of colic as highlighted in the graph below.
From Equine Applied & Clinical Nutrition 2013
Thick, sticky, yellowish fluid secreted by the mare’s mammary gland around the time of birth. Colostrum is loaded with protein, fat, and sugars as well as minerals and particularly immunoglobulins vital to providing immunity to the newborn foal.
In horses, immunity is not transferred from mare to foal before birth – the immunoglobulin molecules are too big to cross the placental barrier. Instead, they are transferred in colostrum immediately after the foal is born. The small intestine of foals is permeable to colostral antibodies for only the first 12- 24 hours of life so there is a short window of time during which colostrum can be effective in providing immunity.
This passive immunity from the dam will help protect the foal from bacterial and viral infections for the first 6-12 weeks by which time its own immune system will be able to take over. Newborn foals should consume 2-4 liters of colostrum as soon as possible after birth. The transfer of immunity can be assessed by use of an IgG test on a blood sample, preferably within the first 24 hours of life. Where immune transfer has failed and the foal’s immunoglobulin levels are low, a plasma transfusion may be recommended by the attending veterinarian to boost immunity.
A good dose of colostrum in the first few hours after birth is the best possible start in life the foal can have whereas the lack of it can have dire consequences laying the foal wide open to a range of potentially serious infections.
Horse feeds are divided broadly into two types, the forage feeds like pasture, hay, silage and haylage, and the concentrate feeds including grains, seeds, by products and manufactured feeds. In general, forages are higher in fibre and concentrates are higher in energy in the form of starch and sugars. The term reflects their being a concentrated source of energy.
a.k.a. Ballerina Syndrome. One of the Angular Limb Deformity syndromes these flexural abnormalities may be present at birth (congenital) or acquired by young foals usually from 1 to 4 months of age and can involve either hyperflexion (knuckling over) or hyperextension (ballerina or down on their bumpers) affecting the fetlock, pastern, or knee joints alone or in combination. Front or hind limbs can be affected, forelimb involvement being more common, and the hock joint rarely involved.
Congenital forms are believed to be due to mare factors including malpositioning of the foetus, influenza during pregnancy, thyroid problems, and lathyrism (poisoning by members of the pea family like Sweet Pea).
Acquired deformity is generally encountered in rapidly growing foals or in conjunction with other painful conditions affecting a limb or foot such as fracture or hoof abscess limiting normal exercise. Growth spurts triggered by excess energy consumption may cause the problem as the long bones grow faster than can be accommodated by the flexor tendons. Treatment depends on type and includes limb splinting, corrective shoeing, restricting, or encouraging exercise, and surgical intervention by check ligament desmotomy (sectioning a supporting ligament).
Essential trace element with multiple functions. It forms part of several enzyme systems responsible for maintaining elastic connective tissues and cartilage, the antioxidant neutralization of free radicals & ROS, preservation of healthy mitochondria, formation of haemoglobin and production of the pigment melanin. Some 66% of total body copper is found in muscle and 20% in bone with significant amounts also present in blood and the liver where it is stored.
Copper is found in forages and grains and often fortified in manufactured feeds. Total tract digestibility of ingested copper is around 40% and may be reduced by competition with Zinc and Cadmium by competition for binding sites in the gut wall. Once absorbed copper passes to the liver where it may be stored prior to use. Copper stores in the liver are laid down by the foetus and carry the newborn foal through the first few weeks of life, so copper status of the pregnant mare may be important.
The bone developmental bone disease Osteochondrosis OCD in foals has been associated with low copper levels in several studies. Whether OCD is actually due to a copper deficiency or whether it can be prevented by raising copper supply above a basic level remains unclear. However, despite fortification of stud feeds with copper becoming standard practice for more than a decade, the rate of OCD on Australian and overseas thoroughbred stud farms has remained stubbornly high, so copper is only a part of that complex story.
Eating manure. Regarded as aberrant or stereotypic behavior it may simply be a response to intermittent feeding in stabled horses driven by time between meals, gut fill, pain from stomach ulcers etc. Insufficient dietary fibre is a potential cause as boosting fibre intake will often reduce coprophagy along with wood chewing and bed eating. High starch diets may also be at fault as replacement of some starch with fat as an energy source may reduce coprophagy. In essence it is a response to modern feeding and management practices and is virtually unknown in wild horses at pasture. Neonate foals will sometimes consume faeces of the dam but this is likely related to simple inquisitive behavior or possibly populating their gut with a normal microbiome.
One of the hormones produced by the Adrenal Gland, Cortisol is a glucocorticoid which acts in opposition to Insulin in the regulation of glucose metabolism. Cortisol enhances the production of glucose from lipids and protein tending to produce a moderate rise in blood glucose concentration, the opposite of insulin.
Formed from a combination of three amino acids, methionine, glycine, and arginine when phosphorylated creatine has the ability to donate a Phosphate group and turn Adenosine Diphosphate ADP into the energy molecule Adenosine Triphosphate ATP. This occurs in muscle cells during exercise and is the reason Creatine has received so much attention as an energy booster. In humans Creatine supplementation has been shown to enhance strength, endurance and the cross- sectional area of muscle fibers in human athletes. As creatine is found mainly in muscle tissues the response was greatest in vegetarians who don’t consume meat. In horses however studies on creatine supplementation failed to show any such effect on muscle or performance under either aerobic or anaerobic conditions. The benefits seen in humans are not reproduced in horses so whilst further research may be justified, at present there is no rationale for use of creatine in horses.
Crib Biting & Windsucking
a.k.a. Cribbing / Windsucking. An example of abnormal stereotypic behavior sometimes called a stable vice. Crib Biting is characterized by the horse first grasping a solid object with the incisors whilst at the same time flexing its neck muscles and drawing air into the oesophagus with a characteristic grunting sound. Windsucking is similar but does not necessarily require the gripping of an object by the teeth first. The movement is repetitive and apparently performs no useful function. It may be learned early in life and follow on from wood chewing. Approximately 4% of all horses will crib bite and the behavior can become dominant, happening hundreds of times daily. It is more common but by no means confined to stabled horses and may reduce in severity or disappear when horses are turned out to pasture. It is not known in wild horses.
Recently there have been suggestions that oral stereotypies like crib biting may be an attempt to increase saliva production for its buffering activity on stomach acid and related reduction in the discomfort caused by stomach ulcers. EGUS should probably be considered as a potential predisposing cause of the condition and treated if present. Cribbing horses have a distinctive gut microbiome but whether that is cause or effect is yet unknown. Deterrents like neck cradles and radical neck surgery (Forcells operation) are no longer seen as appropriate.
See also: Why do they do that? Crib Biting, Stereotypic Behavior and Stable Vices.
Crude Protein is a measure of the protein content of food calculated from its Nitrogen content. It is normally expressed as a percentage or in g/kg of Dry Matter in the food (g/kg DM). For example, a feed label may read 17% CP or 170g/kg. Because CP is calculated from the chemical analysis of all the Nitrogen present in a food, including non-protein Nitrogen like Urea, it may overestimate the true protein content. Non protein Nitrogen, particularly in the form of Urea can be utilised by ruminant herbivores like cows and sheep to make protein, but not by horses which have a low tolerance for Urea.
a.k.a. Equine Cushings Disease. PPID (Pituitary Pars Intermedia Dysfunction) is a disorder of the Pituitary Gland located at the base of the brain. The gland produces hormones under neurologic control by the brain. In Cushings Disease the nerve supply to the gland degenerates or the gland may be affected by a tumor called an adenoma. The amount of Cortisol hormone released into the circulation by the gland increases, affecting the body in several ways. Hair growth is increased (Hirsutism) and shedding of the winter coat is delayed, so these horses tend to look hairy and scruffy. Drinking and urination increase (Polydipsia & Polyuria) as does sweating, and skin infections. The immune system function tends to be depressed and a heavy burden of intestinal parasites may be present and require monitoring and treatment. Body Condition slowly falls away and affected horses loose muscle tone and may appear pot- bellied. They are lethargic and abnormally prone to Laminitis. Usually affecting older horses and ponies over ten years old, the average age of first diagnosis is 19 years.
Diagnosis is based on the history and presence of the above signs and can be confirmed by testing for hormone levels in blood, specifically the hormone ACTH (Adreno Cortico-Trophic Hormone). Diagnosis can be difficult to confirm in the early stages as tests may yield false negatives.
Treatment is usually by the drug Pergolide, a Dopamine agonist which mimics neural control and inhibits excessive hormone production by the pituitary gland. Reportedly effective in 65%-85% of cases, Pergolide treatment is a management tool not a cure.
Some owners elect not to treat horses with only mild symptoms, managing laminitis via dietary modification, excessive hair growth by clipping etc. Diets should aim for low starch and sugar intake (Low NSC) relying primarily on good quality forage feeds like Lucerne and high fibre sources such as sugar beet and soy hulls with added oil for energy if necessary. Pasture access may need restriction in laminitic horses & ponies as the fructan content in pasture grasses may be enough to precipitate a laminitis attack. Whenever repeated episodes of Laminitis occur in aged horses & ponies, Cushings Disease should be considered. Veterinary advice on management is essential.
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Carbohydrates are classified according to the laboratory techniques used to assess them. ADF includes carbohydrate fractions soluble only in acid, principally the woody material Lignin, Cellulose and mineral ash from the plant cell walls. ADF affects digestibility of forage, the higher the ADF, the less digestible it will be. For hay ADF <35% is reasonable but >45% is poor quality and little nutritional value.
Paired endocrine glands lying close to the kidneys they secrete various hormones including the fight flight hormone Adrenaline (epinephrine), plus Norepinephrine. Together these two are called the Catecholamines and are involved in regulating the cardiovascular system and mobilizing fat and carbohydrate stores for energy. Also, Cortisol which helps regulate blood glucose, Aldosterone involved in kidney function and sex hormones (androgen & oestrogen).
Physical exercise which relies on the use of free oxygen in aerobic energy generating processes. Principally carbohydrates are used as fuel and the intensity is low to moderate, so jogging rather than sprinting. As intensity and speed increase Anaerobic systems come into play which do not rely on the presence of free oxygen for energy production.
These comprise a group of Mycotoxins produced by the mould species of the Aspergillus family. Favouring damp warm conditions these moulds may infest grains such as corn, wheat, barley, rice, sorghum, peanut, sunflower and virtually all grains and seeds as well as poorly cured hay. Acute poisoning (Mouldy Corn Poisoning) in the USA is not usually seen in Australia. The toxins principally affect the liver causing chronic damage resulting in ill thrift, poor appetite, anaemia, depression, reduced growth, and poor immunity. Diagnosis is by laboratory screening of feed samples.
Aggressive, fizzy or anxious behavior may be associated with gut pain or discomfort. Abnormal stereotypic behaviors such as wind sucking, crib biting and weaving have been associated with high starch, low forage diets and EGUS. Large starch meals may result in starch overspill into the hind gut with rapid fermentation and lowering the pH there. Hind gut acidity is thought to be a potential cause of gut pain or discomfort and potentially lead to aggressive or irritable behavior. Lowering starch intake, smaller meals more frequently and increasing forage in the ration may reduce the risk.
There are 21 different Amino Acids which form animal proteins. They can be classified according to whether they must be provided whole in the diet (essential) or can be manufactured in the body (non-essential). A third group may have some capacity for manufacture by the body but may become essential in some circumstances such as rapid growth, stress, or illness. These are termed the conditionally essential amino acids.
Not only building blocks for proteins, amino acids play a variety of essential roles in their own right. Adequate dietary supply of amino acids in the form of protein is critical for maintaining health, growth, and tissue repair.
Angular Limb Deformities (bent legs).
Any deviation of a limb from the straight plane. It can arise from the joint(s) or growth plates in long bones, or in the cuboidal bones of the knee or hock. The most common type is an outward slant of the forelimb from the knee joint (Carpus Valgus) and an inward slant of the pastern from the fetlock, away from the midline (fetlock varus). The effect of nutrition is not proven. Causes are believed to include non-symmetric growth in growth plates, trauma, loose slack joints, excessive exercise, and poor limb conformation. See also “Contracted Tendons”.
Cell metabolism normally produces a group of compounds classed as Reactive Oxygen Species (ROS) including peroxides like hydrogen peroxide, free radicals, and unpaired hydroxyl groups. These highly reactive molecules have the capacity to damage proteins, cell membranes and DNA. The body’s natural defense against this damage employs a range of antioxidant compounds to chemically neutralize the ROS and render them harmless. Vitamins A, C and E exert antioxidant effects along with enzymes such as the Selenium dependent Glutathione Peroxidase, and non-enzyme compounds like Lycopene, Lipoic Acid and Ferritin. Supplementation of dietary antioxidants is common practice, especially the use of Vitamin E for horses in hard work which generates more ROS requiring higher antioxidant capacity. Antioxidants are also widely used as preservatives in horse feeds and supplements such as oils to prevent oxidation and rancidity.
Control is via highly complex neurological and hormonal mechanisms involving signaling from nutrients such as glucose and volatile fatty acids, gut fill, the gut hormone Ghrelin which stimulates hunger, and the hormone Leptin from fat tissue which suppresses appetite. Poor appetite can be an issue for performance horses, especially racehorses. Gastric ulceration EGUS is the first cause to be eliminated as gut pain depresses appetite. The old favorite remedy was Vitamin B12 which may have some merit as it is required to metabolize propionate which is increased by high starch diets. Thiamin B1 requirements are also elevated by hard exercise so B Vitamin supplementation may have some value.
The increase in bodyweight in kilograms per day used as a measure of growth rate in young horses. For example, an ADG for a 6-month-old Thoroughbred foal might be of the order of 0.75kg/Day declining to 0.5 kg/Day at age 12 months. Graphs of bodyweight and ADG may be used to ensure growth rate is appropriate for the age of foals and weanlings. ADG is driven primarily by carbohydrate, and to a lesser extent protein intake.
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Also known as Vitamin B7 and sometimes Vitamin H it is part of the water-soluble B Group of vitamins and involved as a component of various enzymes employed in the release of energy from carbohydrates, fats, and protein. It facilitates gene expression and hence cell replication and growth. Biotin is produced naturally by gut microbes in sufficient quantity for normal requirements. It is also present in various feeds, Lucerne and Soya are apparently good sources. Horses with poor hoof horn quality may benefit from supplementation of Biotin, though studies on the rate of hoof growth have been inconclusive. Supplemented Biotin dose rate should be in the range of 3-4mg/100kg bodyweight or 15-20mg/Day for a 500 kg horse fed continuously for at least nine months.
Body Condition.
Assessment of body condition relies primarily on evaluation of the amount of subcutaneous adipose tissue (fat) and is useful for measuring the impact of a nutritional program in individuals. Various scoring systems have been developed to assist evaluation, one of the most popular being the Henneke system dating back to 1983 where a score of 1 indicates extreme emaciation and a score of 9 relates to extremely fat with moderate condition scoring 5. Developed for light breeds like Thoroughbreds and Arabians it may be less accurate for ponies, warmbloods, and draught horses. Other factors such as hair coat length, pregnancy, muscle development, gut fill and evaluator bias may affect scoring but whilst imperfect it remains a useful tool. A rise in score (BCS) over time indicates a positive energy balance with increasing fat accumulation, and declining scores arise when the energy balance is negative and body fat deposits are being utilized as an energy source.
a.k.a. Bone Mineral Density (BMD) is a measurement of the relative proportion of bone mineral versus fibrous tissue matrix in boney tissue. It is an important indicator of skeletal health, strength, and resilience. Methods of measurement include X-Ray, Ultrasound, CT scanning and single photon absorptiometry.
Factors influencing BMD include age and exercise (newborn foals have low BMD at only 17% of adult values whereas yearlings may approach 87% of adult density). Training stimulates re-modelling of bone to strengthen areas under the most stress and generally results in increased BMD. Where training stresses exceed the ability of bone to withstand forces applied, fracture or microfracture may result. The ‘’shin soreness’’ common in young Thoroughbreds undergoing race training is a result of microfractures in the shaft of the cannon bone. As BMD increases during training such damage becomes less likely. Stabling a horse even for a week without access to exercise will significantly reduce BMD even when dietary minerals are plentiful. Dietary mineral intake will influence BMD only when bone is being actively re-modelled, that process being driven primarily by sufficient fast work. Increasing Calcium & Phosphorous intake during training of 2-year-old Thoroughbreds is desirable, along with the use of Omega 3 supplements like flaxseed oil which has been shown to improve the Calcium absorbtion and retention rates.
Caused by a toxin produced by the spore forming anaerobic bacterium Clostridium botulinum which is part of the same family as Clostridium tetani, the causative organism of Tetanus. The bacteria grow in conditions where oxygen is absent such as in rotting vegetation or inside the decaying bodies of small mammals like mice and rabbits. Contamination of hay or other feedstuffs by the bacteria or it’s spores or toxin is the route of poisoning. Poorly ensiled forage or haylage is a possible source as is hay, especially large round bales, contaminated by dead rodents. Often the preformed toxin is consumed but foals may eat the bacterial spores which then develop in their intestine and produce toxin. Botulinum toxin A is the most toxic natural substance known, interfering with nerve impulse transmission, and causing flaccid paralysis.
In horses, signs include weakness, ataxia, difficulty prehending and swallowing food, recumbency with inability to rise, and loss of muscle tone of the jaw, tongue, and tail. Foals may show signs of ‘’Shaker Foal Syndrome” including sudden death, motor paralysis, with inability to suck or stand for more than a brief period. Breathing difficulty, constipation and dilated pupils develop later along with frequent urination, elevated heart rate and fatal respiratory arrest. Samples for testing should include the suspect feed, serum, and intestinal contents. Treatment is by intravenous botulinum antitoxin if available, but prognosis is poor.
Care should be taken with ensiled haylage which has an unpleasant odor like compost or mouldy grass clippings. Haylage should smell sweet and fruity, and any which does not should be discarded. Even a tiny amount of toxin can be lethal from a small area of spoiled feed in a bag or bale. The incidence of Botulism in Australia is rare, perhaps in part because the use of ensiled forage feed is also uncommon here.
Bran.
The type fed to horses is wheat bran, oat bran generally being reserved for human consumption. It is a milling by-product comprising the outer part of the seed coat, which is the first part removed by milling, before the more nutrient rich pollard layer is reached. Bran has an average protein content of about 17% with 24% starch and 7% sugars. Despite its reputation for high fibre, the crude fibre content of bran is quite low at around 10%.
Bran’s big drawback as a feed for horses is its very adverse Calcium: Phosphorous balance. The Phosphorous content is nine times the Calcium, so even a relatively small amount of bran can have a significant negative impact on the overall Ca: P ratio in the diet. When used regularly some additional Calcium should be included to balance the high Phosphorous input. Because of its low fibre content Bran is not actually laxative despite its age- old use for that purpose. It is however highly palatable and enjoyed by horses.
Bran Disease. (Big Head)
Also known as ‘’Millers Disease’’ and ‘’Big Head’’ this condition is a Fibrous Osteodystrophy caused by secondary hyperparathyroidism and is caused by either a deficiency of Calcium or adverse balance between Calcium & Phosphorous.
In classical Bran Disease, millers fed their draught horses on wheat bran because it was cheap and readily available. Bran is very high in phosphorous and very low in calcium, so the diet was calcium deficient. As blood calcium levels fall, the parathyroid gland secretes Parathyroid Hormone which mobilizes bone calcium re-modelling and releases calcium from skeletal stores into the blood to maintain critical blood levels, essential for muscle and nerve function. Slowly the calcium in the skeleton is leached out leaving the fibrous component of bone which proliferates in an effort to shore up the skeletal structure.
The loss of mineral causes bones to soften and pathological fractures may result. Surface bone may flake and tear off where muscles and ligaments attach and pain along with shifting lameness is a feature. Lameness can be subtle and difficult to diagnose. A bunny hopping gait due to hip pain may be noticed along with muscle wastage over the rump especially. The bones of the head, being non weight bearing are sacrificed first and enlarge with fibrous tissue proliferation causing the rounded facial contours and thickened lower jaw typical of Bighead. An old test to confirm the disease was to push an ice pick quite easily through the jawbone. Drooping of the lower lip may be observed, possibly from compression of the nerve supply where it passes through the lower jaw.
Correcting the calcium deficiency will reverse the disease process but may be too late to repair more serious skeletal and joint damage. Supplementation of the diet with ground limestone (Calcium Carbonate) fed at the rate of 60g, and – 120g per day has been found effective. Use of Bran should be restricted care taken to properly compensate the calcium balance of the ration.
Branched Chain Amino Acids (BCAA’s)
These are the amino acids Leucine, Isoleucine and Valine are oxidized by muscle to liberate energy. They are all Essential Amino Acids which means they must be provided in the diet. It has been suggested that supplementing them may improve performance by sparing the use of carbohydrate and glycogen as energy sources, thus reducing lactic acid generation and consequent fatigue. At very low exercise intensity BCAA supplements have been shown to lower blood lactate during and after exercise but at higher intensity no reduction in lactate or improvement in performance were seen.
Provision of supplemental BCAA’s may be of benefit by reducing the catabolism (breakdown) of muscle proteins to liberate them when they are in short supply following exercise. An alternative to BCAA supplements is provision of a group of the six amino acids lost in sweat which may prevent muscle protein breakdown and loss of BCAA’s happening. See Sweat & Amino Acids
These are the remaining materials following fermentation of grains by yeast to digest starch and generate alcohol during the brewing or distilling process. Grains are commonly barley and corn but may include any grain or seed used as a source of starch for commercial alcohol production. Whilst the palatability tends to be quite high due to yeast content and remaining sugars, and the protein level also attractive from a nutrition standpoint, Brewers Grains are potentially dangerous and unsuitable for use as horse feed. The reason is that the product is at high risk of contamination by Mycotoxins such as Aflatoxin and others. Warmth and moisture present during production and subsequent storage are ideal conditions for mycotoxin producing mould growth. These toxins are undetectable without laboratory tests and may be present at dangerous levels without obvious mould in the grains.
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One of the two “Macro Minerals” the other being Phosphorous, calcium is the most abundant element in the body and associated with bones and teeth for good reason as both require it for their physical structure and development. It is a critical component of Calcium Hydroxyapatite the mineral compound from which bone is formed around its collagenous fibrous tissue and cartilage matrices. About 99% of total body calcium is found in bone.
Calcium is also an essential mineral for proper function of nerve and muscle cells and for blood clotting. Without it nerves cannot transmit messages and muscles cannot contract and relax normally. Skeletal calcium acts as a reservoir to maintain serum calcium at normal levels and the circulating calcium level is tightly controlled within narrow margins. The hormones Calcitonin and Parathyroid hormone control calcium flows into and out of bone respectively. If serum calcium falls below normal, disturbances such as muscle weakness or tremors soon develop such as may be seen in the hypocalcaemia associated with “Milk Fever”, more common in cattle and dogs than horses.
Calcium is absorbed mainly (60% to 67%) in the small intestine. It needs to be in ionic form as a divalent cation Ca2+ to be absorbed, and as such other divalent cations like copper and zinc may compete for transport into the body. Acid suppressor drugs like Omeprazole may reduce absorbtion. Oxalic acid found in tropical grasses forms an insoluble salt, calcium oxalate, which reduces digestibility and absorbtion, potentially leading to a functional calcium deficiency and ‘’Big Head’’ (see Bran Disease). Phytic Acid found in cereal grains like oats and barley may also form insoluble complexes with calcium and reduce digestibility. The amount of dietary Phosphorous present does not affect calcium absorbtion and any dietary calcium surplus to immediate requirements is only poorly absorbed. Accretions of calcium in the gut can form stones called enteroliths, fortunately rare in Australia. Excess calcium in the body is excreted through the kidney and under certain conditions may also be associated with kidney and bladder stones (urinary calculi).
Organic compounds comprising Carbon. Hydrogen and Oxygen joined by chemical bonds. Carbohydrates are formed by green plants from carbon dioxide and water in the process of photosynthesis. Essential as energy stores they also form part of the DNA molecule. The basic structural unit is that of a simple sugar or monosaccharide like glucose. These may be joined in pairs to form disaccharides such as sucrose, or chains of three to six called oligosaccharides. In polysaccharides the chains may contain up to thousands of simple sugar units. Examples include starch, cellulose and lignin in plants and glycogen, the principal carbohydrate storage compound in animals. Once ingested by the horse, to release the energy in these complex molecules they must first be broken down by enzyme digestion to yield simple sugars, primarily glucose, or by bacteria to yield volatile fatty acids.
Simple sugars have a molecular size small enough to be absorbed intact through the gut wall into the blood. More complex carbohydrates like starch require digestion by enzymes like Amylase in the small intestine to split the large molecule into simple sugars for absorbtion. Larger polysaccharides like cellulose resist enzyme attack and can only be digested by bacterial fermentation in the hind gut. Those yield mainly volatile fatty acids, not glucose as the energy bearing product.
One important aspect of carbohydrate metabolism in horses is the Insulin Response which can cause problems when horses consume high levels of non fibre carbohydrates like starch in their diet.
The term refers to the heart and blood vessels including arteries, arterioles, capillaries, and veins. Unlike humans, disease of the vascular system (blood vessels) is rare in horses. Heart disease is also relatively uncommon though a range of congenital and acquired defects do occur. Assessment of the system is aided by use of Electrocardiography and Ultrasound examination.
aka L-Carnitine. Necessary for the transport of fatty acids across the mitochondrial cell membrane where they can be oxidized to produce energy in the form of ATP. Mitochondria are tiny organelles found inside cells and act as energy factories for the cell. Carnitine supplements have been touted as an aid to improving muscle energy metabolism and thereby performance. Various studies have produced conflicting results. Carnitine supplements increase plasma carnitine concentration but not the concentration in muscle where it exerts its main effect. To date, studies in horses have not confirmed that the availability of Carnitine is limiting on exercise performance. Whilst Carnitine appears safe to use at recommended supplement dosages there is insufficient scientific evidence that is has any useful effect on muscle metabolism, increases energy or reduces post exercise muscle soreness in horses. Not recommended for use.
Cartilage is a tough flexible connective tissue with variable characteristics depending on its structure and use in the body. Structural cartilage forms the larynx and supports the soft tissue of the nose for example, whilst fibrous cartilage forms the intervertebral discs. Bone is formed on a cartilage matrix in the embryo and persists as cartilaginous epiphyseal growth plates in bones from which they grow, the plates being replaced by bone as the horse matures. A specialized form, articular cartilage, caps the end of the long bones in joints, providing a rubbery shock absorber lubricated by synovial fluid. These protective articular cartilage caps are supported by microscopic boney columns. When the bone columns are defective the overlying cartilage may collapse leaving a cavity in the covering cap as part of the disease called Osteochondrosis Dissecans or OCD. Cartilage in joints is also subject to trauma as well as wear and tear and may become thin or degenerate as part of osteoarthritis.
A minor surgical procedure commonly performed on broodmares to prevent aspiration of air and contaminants into the vagina. After repeated pregnancies the abdominal muscles may become stretched and slack. The abdominal contents fall downwards within the abdomen, including the uterus which in turn pulls the vulva forward and down where it is prone to soiling by faecal material and to aspirating air when the horse breathes. This can predispose to uterine infections (metritis) and is a common cause of infertility in older mares.
The solution is to surgically remove a narrow strip of skin from each side of the upper part of the edge of the vulval lips and suture the two exposed raw edges together when they will fuse within a few days. The operation is performed under local anaesthesia and complications are rare. The joined section of the vulva is opened with scissors just prior to foaling.
Catabolism is the part of Metabolism where large complex molecules are broken down into smaller simpler ones. Its opposite is Anabolism where small simple molecules are assembled into large complex ones. Catabolism includes the processes used to release stored energy from carbohydrates, fats, and amino acids. Catabolic processes can go hand in hand with anabolic ones such as when muscle proteins are catabolized to yield their amino acids some of which are later reassembled to make other proteins. Another example is when fat stores are catabolized to yield fatty acids to be used as a source of energy.
The caterpillars of concern to horse owners and especially breeders are the Processionary Caterpillar PC specifically Ochrogaster lunifer which has been identified as the cause of Equine Amnionitis & Foetal Loss EAFL. First observed in Australia in 2004 as an outbreak of abortions in eastern Australia the syndrome bore similarities to abortions caused in Kentucky in 2001 by the Eastern Tent Caterpillar. These PC were identified in large numbers on affected farms.
A remarkable research project by workers at the University of Queensland demonstrated that the abortions and some pre-term birth of sickly foals was related to placentitis caused by the hairs or setae of these hairy caterpillars. As the caterpillars shed their skin several times during development the dried shed skins with hairs attached build up in large numbers in the environment. Following ingestion by a mare these hairs, which carry barbs, may penetrate the gut wall, and migrate around the abdomen, piercing the uterus and placenta. The setae carry gut and environmental bacteria with them infecting the placenta and causing a bacterial placentitis and abortion. Post- mortem sections of aborted placenta have actually shown setae embedded in them. An individual caterpillar can carry over 2 million setae and a tree containing 100 caterpillars can contaminate an area of 4,000 square meters with 25 setae per square meter. Control is by removing caterpillar nests from stud farms, insecticidal spraying, and habitat tree removal.
A complex carbohydrate comprising hundreds to thousands of chemically bonded D-Glucose units it is the principal structural component of the cell walls of plants. Cellulose is one of the main components of Fibre and cannot be digested by enzymes in the gut. Instead, it is digested by microbes housed in the large intestine and yields Volatile Fatty Acids which are absorbed and utilized to produce energy. An example of pure cellulose is cotton wool and it is thought to be the most abundant of all organic compounds.
The gaseous halide element Chlorine when chemically combined with other elements forms a Chloride. In the body the Chloride ion is the most abundant negatively charged Anion Cl– and is normally found combined with positively charged Cations such as Sodium Na+, Potassium K+ and Magnesium Mg+, the so- called Electrolytes. Together these act to maintain correct fluid balance inside and outside cells as well as maintaining blood volume, blood pressure and the pH of body fluids. Chloride is also required for the production of the Hydrochloric Acid secreted into the stomach.
A water- soluble nutrient sometimes regarded as part of the B Group vitamins. Regarded as essential in some animals it can be manufactured from the amino acid Methionine in the liver and as part of the molecule acetylcholine plays a role in transmitting nerve impulses as well as formation oof phospholipid cell membranes. Neither Choline deficiency or signs of excess have ever been described in horses and it may not even be an essential nutrient in the horse. Choline is widely included in manufactured feeds in the form of Choline Hydrochloride. Claims for choline include curing fatty liver, assisting transport of nutrients across cell membranes, keeping mucus membranes moist and assisting horses with recovery from damage to the central nervous system. Unfortunately, there is no credible evidence to support these or any other claims in the horse.
Comprising part of the glycosaminoglycan (GAG) fraction of the compound Aggrecan which together with Hyaluronan, Keratan Sulphate and collagen fibrils combines to make the structure of Articular Cartilage. Almost invariably used in conjunction with Glucosamine it is claimed to reduce the onset and severity of osteoarthritis by inhibiting enzymes which degrade articular cartilage. Sources include cattle tracheal cartilage, shark cartilage and mussels.
There is some evidence from in vitro laboratory studies that Chondroitin Sulphate and Glucosamine protect against cartilage matrix degradation. Studies in live horses have yielded mixed but generally weak results with perceived bias related to the supplement manufacturers financial support of the studies. Questions remain in regard to the bioavailability of oral supplements which may be low, and the subjective evaluation of lameness measured in some studies.
Extensive studies in humans of Chondroitin Sulphate both in conjunction with, and without Glucosamine have been undertaken, involving thousands of patients mainly with knee and hip pain. Meta analysis of numerous studies concluded that when the trials were properly constituted and managed there was no difference in response between these two joint supplements and a placebo. There is insufficient evidence from credible trials in horses to support the use of either Chondroitin Sulphate or Glucosamine for the treatment or prevention of joint disease.
A trace element purported to improve insulin sensitivity it is sold as Chromium Picolinate, Chromium Propionate and chelated in Chromium yeast. Some studies in humans indicated positive response to chromium supplementation with improved glucose tolerance in insulin resistant patients. Limited trials in horses yielded conflicting results with slightly lowered peak insulin response to an oral starch challenge test in one experiment, and no significant effect in another larger longer trial. Further research is needed to determine whether or not Chromium has value in the management of Insulin Resistance or potentially Laminitis n horses. Chromium deficiency has never been recorded in horses indicating that normal dietary intake is likely sufficient. Meanwhile Chromium is heavily promoted as enhancing athletic performance, improving health and reducing insulin resistance with scant if any justification.
An essential trace element essential for the formation of Vitamin B12 (Cobalamin) which is manufactured by microbial activity in the hind gut of horses. Essential with Vitamin B12, copper and iron for the formation of red blood cells. Also involved in energy metabolism in complexes with other compounds including production of glucose from volatile fatty acids. Cobalt is absorbed in the hind gut as part of cobalamin complexes formed by gut microbes. Where dietary cobalt is deficient the symptoms would be those of Vitamin B12 deficiency. An intake of 0.5 – 0.6mg per day for a 500kg horse is deemed adequate. Cobalt was tried as a performance enhancer following suggestions in lay press that high doses may stimulate erythropoietin (EPO) production and it was used in competitive cycling and then by some horse trainers in 2013. Racing authorities intervened and set pre- or post- race urine levels of 100 micrograms per liter above which the Rules of Racing may be breached. There has been some controversy over what constitute the ‘’normal’’ range of cobalt in the horse population as it can come from a variety of legitimate natural sources. Appropriate care should be taken if using Cobalt containing feeds or supplements in competitive sport / racehorses.
Colic
Colic means a pain in the belly. It is a symptom, not a diagnosis. Causes are many and varied and colic ranges from mild and transient to severe and fatal so it should always be treated seriously. Most but not all colic’s are related to poor feed management. A sample of different types is listed below:
Gas – most commonly resulting from fermentation of carbohydrates in the large intestine (hind gut) by gas producing bacteria. The carbs can be starch from concentrate feeds like grains, or sugars including fructans in pasture or hay. Gaseous distension of the bowel causes stretching of the wall and pain. Complications locally can include gut stasis and displacement of parts of the bowel with subsequent compromise to the blood supply. Toxins from leaky bowel wall can enter the circulation and precipitate an attack of laminitis.
Obstruction – Can be a physical obstruction by e.g., sand or an accumulation of indigestible fibrous food such as poor- quality hay or straw bedding, or subsequent to a disturbance to the normal motility of the gut with displacement, folding or twisting of a section of bowel. In foals, a specific obstructive colic can be caused by intussusception when a length of gut sleeves in on itself compromising its blood supply and choking off the flow of ingesta. Hernias both internal inside the abdomen, and through the abdominal wall can also obstruct lengths of gut. Enteroliths are accretions of calcium salts forming stones in the gut which may occasionally cause obstruction.
Displacement – often subsequent to gas or a disturbance in normal motility, a length of bowel, either small or large intestine moves or floats to an abnormal position causing twisting of the supporting connective tissue (mesentery) and again, occlusion of blood supply. Requires surgery to correct.
Toxins – a variety of toxins from sources such as poisonous plants, mycotoxins from mouldy feed, contaminants such as heavy metals like lead and certain chemicals such as pesticides can be ingested and result in abdominal pain as one of the symptoms of poisoning.
Spasmodic – A symptom rather than a cause as the name implies spasm of intestinal smooth muscle comes intermittently in waves associated with pain of varying intensity.
Causes are too numerous to cover in detail here. Abrupt changes in feed predispose to colic as does stabling and lack of access to pasture. High grain low forage diets are strongly correlated with higher incidence of colic as highlighted in the graph below.
From Equine Applied & Clinical Nutrition 2013
Thick, sticky, yellowish fluid secreted by the mare’s mammary gland around the time of birth. Colostrum is loaded with protein, fat, and sugars as well as minerals and particularly immunoglobulins vital to providing immunity to the newborn foal.
In horses, immunity is not transferred from mare to foal before birth – the immunoglobulin molecules are too big to cross the placental barrier. Instead, they are transferred in colostrum immediately after the foal is born. The small intestine of foals is permeable to colostral antibodies for only the first 12- 24 hours of life so there is a short window of time during which colostrum can be effective in providing immunity.
This passive immunity from the dam will help protect the foal from bacterial and viral infections for the first 6-12 weeks by which time its own immune system will be able to take over. Newborn foals should consume 2-4 liters of colostrum as soon as possible after birth. The transfer of immunity can be assessed by use of an IgG test on a blood sample, preferably within the first 24 hours of life. Where immune transfer has failed and the foal’s immunoglobulin levels are low, a plasma transfusion may be recommended by the attending veterinarian to boost immunity.
A good dose of colostrum in the first few hours after birth is the best possible start in life the foal can have whereas the lack of it can have dire consequences laying the foal wide open to a range of potentially serious infections.
Horse feeds are divided broadly into two types, the forage feeds like pasture, hay, silage and haylage, and the concentrate feeds including grains, seeds, by products and manufactured feeds. In general, forages are higher in fibre and concentrates are higher in energy in the form of starch and sugars. The term reflects their being a concentrated source of energy.
a.k.a. Ballerina Syndrome. One of the Angular Limb Deformity syndromes these flexural abnormalities may be present at birth (congenital) or acquired by young foals usually from 1 to 4 months of age and can involve either hyperflexion (knuckling over) or hyperextension (ballerina or down on their bumpers) affecting the fetlock, pastern, or knee joints alone or in combination. Front or hind limbs can be affected, forelimb involvement being more common, and the hock joint rarely involved.
Congenital forms are believed to be due to mare factors including malpositioning of the foetus, influenza during pregnancy, thyroid problems, and lathyrism (poisoning by members of the pea family like Sweet Pea).
Acquired deformity is generally encountered in rapidly growing foals or in conjunction with other painful conditions affecting a limb or foot such as fracture or hoof abscess limiting normal exercise. Growth spurts triggered by excess energy consumption may cause the problem as the long bones grow faster than can be accommodated by the flexor tendons. Treatment depends on type and includes limb splinting, corrective shoeing, restricting, or encouraging exercise, and surgical intervention by check ligament desmotomy (sectioning a supporting ligament).
Essential trace element with multiple functions. It forms part of several enzyme systems responsible for maintaining elastic connective tissues and cartilage, the antioxidant neutralization of free radicals & ROS, preservation of healthy mitochondria, formation of haemoglobin and production of the pigment melanin. Some 66% of total body copper is found in muscle and 20% in bone with significant amounts also present in blood and the liver where it is stored.
Copper is found in forages and grains and often fortified in manufactured feeds. Total tract digestibility of ingested copper is around 40% and may be reduced by competition with Zinc and Cadmium by competition for binding sites in the gut wall. Once absorbed copper passes to the liver where it may be stored prior to use. Copper stores in the liver are laid down by the foetus and carry the newborn foal through the first few weeks of life, so copper status of the pregnant mare may be important.
The bone developmental bone disease Osteochondrosis OCD in foals has been associated with low copper levels in several studies. Whether OCD is actually due to a copper deficiency or whether it can be prevented by raising copper supply above a basic level remains unclear. However, despite fortification of stud feeds with copper becoming standard practice for more than a decade, the rate of OCD on Australian and overseas thoroughbred stud farms has remained stubbornly high, so copper is only a part of that complex story.
Eating manure. Regarded as aberrant or stereotypic behavior it may simply be a response to intermittent feeding in stabled horses driven by time between meals, gut fill, pain from stomach ulcers etc. Insufficient dietary fibre is a potential cause as boosting fibre intake will often reduce coprophagy along with wood chewing and bed eating. High starch diets may also be at fault as replacement of some starch with fat as an energy source may reduce coprophagy. In essence it is a response to modern feeding and management practices and is virtually unknown in wild horses at pasture. Neonate foals will sometimes consume faeces of the dam but this is likely related to simple inquisitive behavior or possibly populating their gut with a normal microbiome.
One of the hormones produced by the Adrenal Gland, Cortisol is a glucocorticoid which acts in opposition to Insulin in the regulation of glucose metabolism. Cortisol enhances the production of glucose from lipids and protein tending to produce a moderate rise in blood glucose concentration, the opposite of insulin.
Formed from a combination of three amino acids, methionine, glycine, and arginine when phosphorylated creatine has the ability to donate a Phosphate group and turn Adenosine Diphosphate ADP into the energy molecule Adenosine Triphosphate ATP. This occurs in muscle cells during exercise and is the reason Creatine has received so much attention as an energy booster. In humans Creatine supplementation has been shown to enhance strength, endurance and the cross- sectional area of muscle fibers in human athletes. As creatine is found mainly in muscle tissues the response was greatest in vegetarians who don’t consume meat. In horses however studies on creatine supplementation failed to show any such effect on muscle or performance under either aerobic or anaerobic conditions. The benefits seen in humans are not reproduced in horses so whilst further research may be justified, at present there is no rationale for use of creatine in horses.
Crib Biting & Windsucking
a.k.a. Cribbing / Windsucking. An example of abnormal stereotypic behavior sometimes called a stable vice. Crib Biting is characterized by the horse first grasping a solid object with the incisors whilst at the same time flexing its neck muscles and drawing air into the oesophagus with a characteristic grunting sound. Windsucking is similar but does not necessarily require the gripping of an object by the teeth first. The movement is repetitive and apparently performs no useful function. It may be learned early in life and follow on from wood chewing. Approximately 4% of all horses will crib bite and the behavior can become dominant, happening hundreds of times daily. It is more common but by no means confined to stabled horses and may reduce in severity or disappear when horses are turned out to pasture. It is not known in wild horses.
Recently there have been suggestions that oral stereotypies like crib biting may be an attempt to increase saliva production for its buffering activity on stomach acid and related reduction in the discomfort caused by stomach ulcers. EGUS should probably be considered as a potential predisposing cause of the condition and treated if present. Cribbing horses have a distinctive gut microbiome but whether that is cause or effect is yet unknown. Deterrents like neck cradles and radical neck surgery (Forcells operation) are no longer seen as appropriate.
See also: Why do they do that? Crib Biting, Stereotypic Behavior and Stable Vices.
Crude Protein is a measure of the protein content of food calculated from its Nitrogen content. It is normally expressed as a percentage or in g/kg of Dry Matter in the food (g/kg DM). For example, a feed label may read 17% CP or 170g/kg. Because CP is calculated from the chemical analysis of all the Nitrogen present in a food, including non-protein Nitrogen like Urea, it may overestimate the true protein content. Non protein Nitrogen, particularly in the form of Urea can be utilised by ruminant herbivores like cows and sheep to make protein, but not by horses which have a low tolerance for Urea.
a.k.a. Equine Cushings Disease. PPID (Pituitary Pars Intermedia Dysfunction) is a disorder of the Pituitary Gland located at the base of the brain. The gland produces hormones under neurologic control by the brain. In Cushings Disease the nerve supply to the gland degenerates or the gland may be affected by a tumor called an adenoma. The amount of Cortisol hormone released into the circulation by the gland increases, affecting the body in several ways. Hair growth is increased (Hirsutism) and shedding of the winter coat is delayed, so these horses tend to look hairy and scruffy. Drinking and urination increase (Polydipsia & Polyuria) as does sweating, and skin infections. The immune system function tends to be depressed and a heavy burden of intestinal parasites may be present and require monitoring and treatment. Body Condition slowly falls away and affected horses loose muscle tone and may appear pot- bellied. They are lethargic and abnormally prone to Laminitis. Usually affecting older horses and ponies over ten years old, the average age of first diagnosis is 19 years.
Diagnosis is based on the history and presence of the above signs and can be confirmed by testing for hormone levels in blood, specifically the hormone ACTH (Adreno Cortico-Trophic Hormone). Diagnosis can be difficult to confirm in the early stages as tests may yield false negatives.
Treatment is usually by the drug Pergolide, a Dopamine agonist which mimics neural control and inhibits excessive hormone production by the pituitary gland. Reportedly effective in 65%-85% of cases, Pergolide treatment is a management tool not a cure.
Some owners elect not to treat horses with only mild symptoms, managing laminitis via dietary modification, excessive hair growth by clipping etc. Diets should aim for low starch and sugar intake (Low NSC) relying primarily on good quality forage feeds like Lucerne and high fibre sources such as sugar beet and soy hulls with added oil for energy if necessary. Pasture access may need restriction in laminitic horses & ponies as the fructan content in pasture grasses may be enough to precipitate a laminitis attack. Whenever repeated episodes of Laminitis occur in aged horses & ponies, Cushings Disease should be considered. Veterinary advice on management is essential.
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