Q: I have a question about brewers yeast for horses. Can it help the digestive system, hoof health, and improve fiber digestion?
Yeast appears to have an important role in the microbial digestion process, but the precise mode of action has not been identified. Yeast also appears to improve feed palatability, which helps horses maintain a more consistent feed intake. Therefore, yeast may help overcome the negative effects of less palatable feeds.
Feeding yeast to horses falls into 2 categories: dead and alive. Dead: brewer's yeast is one of the by-products derived from brewing. In the dry form, the brewer's yeast contains a relatively high concentration of high quality protein, and is also a good source of fat, water-soluble B vitamins (exception is B12) and the mineral phosphorus. It is sometime fed to horses in poor condition at the rate of 30 - 50 g/day, but is usually too expensive to feed regularly.
Live: yeast cultures of live yeast organisms are also used as a probiotics - live organisms that are fed daily and potentially have a positive role in the microorganism populations in the hind-gut. The most common strains of yeast fed as probiotics are Saccharomyces cerevisiae, Aspergillus oryzae and Torulopsis.
Based primarily on work with ruminants (cattle), live yeast cultures have been shown to synthesize a wide variety of enzymes that are able to break down fiber and proteins. Researchers have tested over 50 strains of S. cerevisiae and found only seven strains with the ability to stimulate growth of fiber-digesting bacteria. Consequently, these yeast cultures can aide in the digestion of forages, and to a limited extent, proteins and carbohydrates in grains (limited because most of the digestion of cereal grains occurs in the foregut of the horse).
The effectiveness of probiotics in horses of various ages is somewhat questionable. Investigations have shown that the effect of time since manufacturing, temperature variations, and acidity in foregut can all have an impact on viability of probiotics microorganism. Many of the probiotics available have been isolated and cultured from species different from the horse, and therefore may not be compatible with the equine gastrointestinal tract environment.
There have been a few studies which indicate that feeding live yeast cultures to young growing horses may have some benefit, with no advantage for the mature, healthy horse.
Horses with some conditions do seem to benefit, but without further studies, these products fall into the "can't hurt, may help" category.
By Hathaway, PhD & Valberg, DVM, University of Minnesota