Pedigree Query

I moved my horses and 1 client to a new farm-the farm is awesome, but I/we suspect that we are going to have some fly issues. My Thoroughbred gelding & my clients Thoroughbred mare are very thin skinned and I am worried about how they are going to react. My warmblood gelding hates flys, but he has never had any "effects" from them.
I used to hear that garlic is awesome, but have been hearing some negatives lately-any other natural feed supplements that are going to help our horses-that the rest of the horses don't have to be on.