While many people feed garlic and report no ill effects, the clinical signs might not be obvious and depending on the dose, frequency, and duration of the dose given there could be low-grade deleterious effects. | Photo: iStock

Q: I am always looking for natural ways to repel flies in my barn and I have heard that feeding garlic can stop flies from bothering horses. Does this work and is it safe to feed garlic to horses?

A: Garlic is touted for several beneficial functions, including respiratory health (it is supposed to alter the physical properties of mucus), antibacterial, and antimicrobial properties, and its supposed ability to repel insects. The thinking is that feeding garlic creates an odor in sweat that helps repel flies.

Garlic and other members of the onion family are rich sources of organic sulfur compounds (in organic chemistry, “organic” means a compound contains a significant amount of carbon). One of the many sulfur compounds present in garlic is a thiosulfate, which has been associated with antibacterial and antiparasitic properties found in allicin (a pungent, oily liquid in