Touted as antiseptic, antibiotic, and anti- inflammatory as well as being an effective ‘’blood cleanser’’ generally without any explanation of what a ‘’blood cleanser’’ actually is. Garlic is also reputed to repel flies, midges and mosquitos and aid in clearing mucus from the respiratory system.
The active component in garlic is thought to be the compound allicin released by crushed garlic and shown to have some antibacterial and antiparasitic properties. One study indicated that garlic supplementation reduced tracheal exudate and the number of neutrophils in the tracheal wash fluid, indicative of possible reduced tracheobronchial inflammation.
Garlic is toxic if overdosed as it contains toxic N-propyl disulphide. Gastric irritation is possible, and also a specific type of anaemia caused by denaturing haemoglobin which results in the haemoglobin forming clumps called Heinz bodies in the red blood cells. Applied topically garlic oil may cause skin irritation.
Whilst more data on safe long term intake levels is needed, an intake of 15mg/kg bodyweight dried garlic powder is regarded as safe – this equates to 7.5 grams for a 500 kg horse. Double that amount may be sufficient to cause mild anaemia.
On balance, solid scientific support for garlic use is lacking but there is evidence of toxicity if conservative dosing is exceeded. On that basis there seems to be little to recommend it.