No abstract

Twenty-four primiparous Holstein cows were fed corn silage:grain (1:1, DM basis) and hay (.9 kg/d) beginning 30 d prepartum and through wk 18 of lactation. Ten grams of Biomate Yeast Plus (5 X 10(9) cfu of Saccharomyces cerevisiae/g) were top-dressed on the a.m. allotment of corn silage:grain fed to 12 cows. Corn silage:grain was restricted during prepartum and thereafter fed for ad libitum intake. Cows fed supplemental yeast peaked earlier and had a higher milk yield compared with control cows (wk 7, 29.5 kg/d vs. wk 11, 28.7 kg/d). Digestibilities of protein and cellulose were improved in cows fed supplemental yeast, contributing to a greater DMI during the first 6 wk of lactation and a higher average milk yield through wk 18 of lactation compared with control cows (27.2 vs. 26.0 kg/d).

Thirty-six multiparous Holstein cows were fed a mixture of corn silage and concentrate [1:1; dry matter (DM) basis] and long hay (0.9 kg/d) through wk 18 of lactation. Beginning at 30 d prepartum through wk 4 of lactation, the total mixed rations of 18 of these cows were top-dressed daily with 10 g of Biomate Yeast Plus (Chr. Hansen's, Inc., Milwaukee, WI). The other 18 cows served as controls. At wk 5, both control and treated cows were divided into three groups and fed 0, 10, or 20 g/d of yeast. Yeast supplementation during early lactation significantly improved DM intake, milk yield, and the digestibility of crude protein and acid detergent fiber. Least squares means for DM intake, fat-corrected milk yield, crude protein digestibility, and acid detergent fiber digestibility for cows fed 0, 10, 20 g/d of yeast during wk 5 to 18 of lactation were 23.8, 24.7, and 25.0 kg/d; 37.7, 40.7, and 41.4 kg/d; 78.5, 80.8, and 79.5%; and 54.4, 60.2, and 56.8%, respectively. Although numerical responses in DM intake and milk yield were greater for cows fed 20 g/d of yeast than for cows fed 10 g/d of yeast, the response was not significant.

Thirty Holstein cows were fed diets of 50% grain and 50% corn silage (dry matter basis) through the first 18 wk of lactation. Grain mixes were supplemented with inorganic calcium sources (aragonite, calcite flour, or albacar) to provide .6 or .9% dietary calcium (dry matter basis). Phytate phosphorus intake averaged 38.3 and 42.6 g/d in digestion trials conducted during wk 4 and 10 of lactation, respectively. Even though large quantities of feed and significant amounts of grain were consumed, 98% of dietary phytate phosphorus was hydrolyzed to inorganic phosphorus. Neither calcium source nor calcium quantity affected the hydrolysis of phytate phosphorus.

Valine, leucine, and isoleucine were extracted by the lactating bovine mammary gland in excess of outputs in milk protein. Carbon-14 uniformly labeled L-valine, L-leucine or L-isoleucine were catabolized when incubated in vitro with lactating bovine mammary tissue slices. The pathways of degradation of these amino acids by mammary tissue appear to be those common to other tissues. These amino acids represent a potential source of energy to the mammary gland as well as a source of carbon and alpha-amino nitrogen for synthesis of nonessential amino acids.