Obesity is the excessive accumulation of fat to the extent that it impacts negatively on the health of the horse. Horses with a body condition score of ≥7/9 are considered obese (on a scoring system of 1-5 the cut off for obesity is 3/5). Very many horses are obese and because it is so common it is often unrecognised by owners and some degree of obesity is becoming the norm.
Obesity is linked to Equine Metabolic Syndrome (EMS) with associated risk of laminitis. It is a risk factor for Insulin Resistance and prevalent in horses with PPID. Other risks to obese horses include orthopaedic disease / osteoarthritis, infertility, hyperthermia, hyperlipaemia, increased risk of colic and reduced athletic performance. Obese broodmares are more likely to have foals which suffer from osteochondrosis dissecans OCD. Obesity impacts negatively on horse welfare as well as health.
Estimates of the prevalence of obese horses in various populations of horses in the UK range from ~35% to ~72% with native pony breeds being over represented as are horses used for pleasure rather than competitive riding. Owners are generally poor at assessing their horses body condition and identifying overweight individuals. Belly girth is a useful indicator of body fat and fat loss when diet changes are made. Heart girth and rump width can also be measured with suitable weight tapes.
Weight reducing diets should aim for a target of 0.55% to 1.0% of bodyweight loss per week by reducing mainly the NSC content of the ration.