What do y’all use for fly prevention that can be fed in feed? TIA

I feed Solitude IGR. 

http://www.sweetpro.com/horse-equilix.html

this is suppoes to help with flies. We tried it this spring, before the bugs came out, 2 of our horses wouldn't touch it, the other 2 inhaled it. I was going through 50# tub in a week. So I quit feeding it. 

It might be worth it to see if it works for fly control. 

I am feeding smartpack Bug Off to one horse. And Leg up bug defense to the other two.

I want to compare since the Leg up is a little cheaper. Bug Off works well. I have also used Buggzo with good results. I have used a feed through like Simplify as well, and it probably helped cut down the population. I feel like its worth it. They seem to stomp less. They are out in a big pasture so I can't use sheets etc.

I can't use the Tubs because I have a horse that thinks he is a pig and will destroy and inhale anything left out there

A friend of mine has fed food grade garlic powder for years with good results.

How would you know how much garlic to add to feed?

I have feed Smart Bug Off to my buckskin mare for a few years with I thought pretty good results.  When I got her the flies just were all over her vs. my other two.  I just bred her this year and Smart Paks can't guanrantee that it's safe for bred mares so I took her off of it.  Just like that the flies are back all over her.  I definitely think it works!