Enhanced Nitrogen Retention in Yearling Horses Supplemented with Yeast Culture

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 × 4 Latin-square design 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.