Corn oil is high in Omega-6, which aggravates inflammation.
I prefer to feed Omega-3 Horseshine which has the correct balance of Omega-3's to -6's.
If you don't want to do that, Canola oil is high in Omega-3 but still shouldn't be over fed.
I have been feeding garlic to my horses since spring 2004 for tick control. It is 85% effective against ticks. I always say it doesn't do a lot for flies because the midge flies and other no-see-ums bite them no matter what I do (spray or no spray, garlic or no garlic).
That being said, I barely spray my horses for daily turnout but they do not live in a crowded environment. Even though we are surrounded by beef farms, you can't see them. I only have four horses on 22 acres, so fly control isn't a huge issue for me.
It's probably too late in the season to start a horse on garlic for any kind of bug control, but it is also good for the immune system. I keep my horses on equine processed
(not raw) garlic until mid-November; they go back on garlic in mid-March.
That was pretty much a "yes, I guess not" answer wasn't it