Brewer's Yeast Slurry. II. A Source of Supplementary Protein for Lactating Dairy Cattle

Abstract

Brewer's yeast slurry and soybean meal each were incorporated in complete rations at 6 and 12% of dry matter to increase crude protein from 13% (negative control) to 15 and 17%. Thirty Holstein cows were blocked on age, stage of lactation (average 200 days), and milk yield (average 19.4kg) and assigned to treatments within blocks. Data analysis was on differences between the 28-day treatment and average of preceding and subsequent control periods when the 15% protein soy diet was fed.Milk yield, milk component yields, and differences of protein percent were higher on the supplemented rations than on the negative control. Differences in protein and solids-corrected milk yield increased with dietary crude protein. Source of supplementary protein did not affect production response. A taste panel test detected no difference in organoleptic quality of milk representative of each treatment ration.Molar percent of rumen acetic acid was higher on the yeast supplemented rations while propionic and isovaleric acids were lower. Blood urea nitrogen was also lower from supplementation with yeast slurry. Apparent digestion coefficients for dry matter, gross energy, crude protein, and acid detergent fiber were all higher on the yeast supplemented rations than on soy diets.The effect of yeast slurry stored for 0, 7, or 14 days on rumen measures was compared with a soybean meal control diet in a 4×4 Latin square experiment with rumen fistulated cattle. Storage time had no consistent effect on measures of rumen or blood.