Diets consisting of whole shelled corn and a commercial pelleted feed were fed to growing
yearling Thoroughbred horses with and without supplementation with urea or dried live yeast
culture, in a 4 X 4 Latin-square desigo adjusted to account for residual effects. Supplementation
with live yeast culture resulted in 7 to 13 g increases in daily net nitrogen retention as well as
increases in hemicellulose digestibility. The proportion of fecal nitrogen that was water-soluble and
therefore absorbable increased 47% with the addition of dried live yeast culture to the basal (corn
and pellets) diet, suggesting that microbial production of ammonia and amino acids was enhanced.
In contrast, the proportion of fecal nitrogen that was cell-bound increased 65% when the live yeast
culture was added to the urea-containing diet, suggesting that the yeast culture acted by stimulating
the conversion of recycled urea to microbial protein and amino acids.
(Key Words: Horses, Yeast, Nitrogen, Feed Conversion, Urea.)