if its not found in your horse’s feed, whats the purpose of supplementing with it? I saw its high in Vit B and aids with fiber digestion.
Just curious as Im reading different things online about it.
I use it in conjunction with soybean oil as a weight supplement. It was suggested by a friend, and I started a two year old on it who is this super fit, not-a-shred-of-fat-on-him type athlete, and it works very well. I would have to do some searching again to refresh my memory on how exactly it works, but many high fat supplements contain brewers yeast. It’s a great cheap fat supplement without spending out the nose for higher end stuff that essentially does the same thing.
My 96 year old great aunt who was a horsewoman always swore by Brewer’s Yeast for her dogs and horses. She said it made their coats look phenomenal and it was cheap. She gave a little bit to them every day.
I must say, all her animals look gorgeous in the old photos. 
You need the right kind of yeast in the right amount. It’s a fungus, NOT a fat supplement. Yeast MAY enhance the activity of good (beneficial) hind-gut activity in your horse. OP, if you are reading online, try to find peer reviewed articles or at least those from reputable sources (ie universities). Triple Crown has a vast library of articles if you want to flip through that website. PS - what goes for one species does not necessarily go for others, and equine/human digestion are so very different.
“A leading feed company recently published, through their online blog, information concerning the lack of benefits of yeast cultures in horse feed diets. This company is also one of the only companies in the US that does not include yeast cultures in their feeds based on “in house” research. In actuality, independent research analyzing the advantages of yeast cultures in horse feeds has been examined over the past 20 years. The American Assn. of Feed Control Officials (AFFCO) defines yeast cultures as “the dried product composed of yeast and the media on which it was grown, dried in such a manner as to preserve the fermenting activity of the yeast.” The most recent National Research Council (NRC) recommendation states “Variation in observed responses between studies may be attributed to differences in the amount of yeast supplementation being fed, composition and treatment of diet interaction, and diet adaptation time. Results across the studies suggest some potential benefits to feeding yeast when high starch or low fiber diets are being fed. Improvements in nutrient digestibility, especially nitrogen, are suggested, but the exact mechanism for this response is not evident. Constant feeding of yeast may have greater potential for mediating an effect as compared to sporadic supplementation.” As with most nutrients in horses, the NRC does suggest further studies.” - See more at: https://www.triplecrownfeed.com/articles/triple-crown-horse-feed-there-any-benefit-yeast-cultures-horse-feeds/#sthash.lukn9wiS.dpuf
