Garlic, horses and mosquitoes
As eastern equine encephalitis season is in full swing in some areas and West Nile virus cases should be starting soon, the need to avoid the vectors of these diseases, mosquitoes, is clear. There are various ways to reduce exposure to mosquitoes, but none of them are great, in terms of their effectiveness and practicality. In peoples' quests to find alternative approaches, they often come across garlic. Ingestion of garlic has been advertised and used as a mosquito repellent in humans and horses.
But, does it work?
I've heard many anecdotes about peoples' success (or lack thereof) with feeding their horses garlic or garlic components. Some people have said they thought it worked. Others, probably the majority, didn't think it worked anything.
The scientific literature doesn't help much. Despite what you read on internet sites selling garlic, there's no published work on garlic as a mosquito repellent in horses. There's a little research involving humans but no effect has been identified. A study that involved giving people garlic or placebo, then exposing them to mosquitoes and counting the number of bites and weights of the mosquitoes after exposure (the more the blood they ingest, the more they weigh) showed no effect of garlic (Rajan et al 2005). Beyond that, there's nothing else out there.
Lack of scientific evidence doesn't necessarily mean lack of effectiveness. It could just be that adequate studies haven't been performed. However, that doesn't change the fact that there is currently nothing indicating that garlic is an effective mosquito repellent. There's probably no harm in giving reasonable doses of garlic as part of an overall mosquito control program, but it shouldn't be done in place of other activities such as reducing mosquito breeding grounds and avoiding high risk areas (particularly at dawn and dusk).
