Garlic is one of those things that everyone has different opinions about.
My own personal experience/education about garlic is that it doesn't have much positive effect on your dogs health, and it can, in big doses, be harmful - causing gut upsets or allergic reactions, and that sort of thing. As far as I know, not enough research has been done for a standard "too high" dose to be defined, so its kind of tricky knowing how much is too much.
Its believed that garlic can be used as a home remedy for worms and fleas. As far as I know its not true, and its a potential hazard to try it for the above reasons. On top of that, garlic can, just like in humans, give your dog bad breath!
This is just my opinion, others may have information to back up another view, pro-garlic or neutral. Its really a personal view I guess, kind of like feeding grains to your dog. You can always ask your vet what they think, and see what kind of information they can give you
I don't know if this helps but my Vet told me to never give my dog onion, garlic or chocolate under any circumstances so I believed him seeing as he had attended the course at university but as you say I have never actually investigated this myself. Maybe I should do a little digging but Steel has never suffered by not having any of these.
