Garlic can exacerbate inflammatory problems like sweet itch or gastric ulcers. It can also deplete the good microbes in the horses gut and cause scouring.
Take care garlic feeders! Just because something has been done for years doesn't mean that - as we understand more about it - it's still right. Take little boys up chimneys and cigarette smoking (which was actually promoted as good for your lungs about 50 years back!) If you dig a little deeper, there is new research coming out that shows - as Diggerdog so eloquently advises - that feeding garlic can cause gastric ulcers, scouring and other problems. There is also no scientific evidence that I know of that clearly evidences that horses smelling of garlic are less likely to be attacked by flies. We all like to THINK we're helping but believe me I've seen horses regularly fed vast quantities of garlic surrounded and plagued by just as many flies as non garlicky horses. Take care. You could be causing more harm than good to your ned! x
We have always fed garlic and not had any problems,
I also did my a level course work on it and used it to show that it could kill worms in the horses gut
A friend of mine started using Think Fly last year and absolutely swears by it now for controlling the fly nuisance of summer. Might be an alternative for using the garlic if you're worried. Have smelled the Think Fly and it doesn't smell garlicky. Not sure what's in it but it's definitely worth a try if my friend's experience of the product is to be believed.
Also saves the aggro of having to apply topical repellents (which in my experience rarely work, or if they do, not for very long before needing re-application).