Supplemental yeast culture alters the plasma amino acid profiles of nursling and weanling horses

Abstract

Summary The ability of a dietary supplement of dried live yeast culture to influence the growth rates, feed conversion efficiency and plasma amino acid profiles of young horses was tested. 10-week old nursling foals fed a creep feed of corn, oats and pelleted alfalfa, made available at 1% bodyweight daily, were also given 10 g yeast culture per day, mixed with granulated sugar and fed by hand. The nurslings remained with their dams and were allowed to continue to nurse freely throughout the 7 weeks of the experiment. In a second, preliminary trial, 6–9 month old weanlings were fed a ration consisting of crimped oats, alfalfa hay, a pelleted concentrate/roughage mix and cracked corn, at 2% of bodyweight daily, with or without supplemental yeast culture (20 g/day). Jugular venous blood samples were drawn from supplemented and unsupplemented animals during each trial after 0, 2, 4, 6, 8, 22 and 36 days, and from the nurslings again at 50 days. Significant increases in the plasma concentrations of arginine, glutamine, lysine, methionine and valine and significant decreases in ammonia, hydroxyproline and 3-methylhistidine were observed in the supplemented nurslings after 6–22 days. Compared to an unsupplemented weanling fed the same diet, 4 supplemented weanlings exhibited significant increases in plasma arginine, glutamine, glycine, isoleucine, leucine, methionine and valine concentrations, while ammonia, hydroxyproline and 3-methlylhistidine concentrations decreased. Rates of gain were significantly increased in both groups of supplemented foals, and feed conversion efficiency by weanlings improved 8% with supplementation. These findings suggest that supplemental yeast culture may influence amino acid balances and nitrogen metabolism in young horses, resulting in enhanced growth.