Voluntary Feed Intake, Milk Production, Rumen Content, and Plasma-Free Amino Acid Levels of Lactating Cows on Low Sulfur and Sulfur-Supplemented Diets

Twenty-four mature lactating Holstein cows were divided equally into two groups. One group received a concentrate mixture containing 0.10% sulfur and the other group received the same concentrate mixture supplemented with Na 2 SO 4 · 10H 2 O. Both groups of cows received the same corn silage, which contained 0.09% sulfur on a dry basis. The corn silage and concentrate mixture was fed ad lib. at a constant ratio of 6.3 to 1.0 for nine weeks. Voluntary feed intake and milk production were signifleantly higher for the sulfur-supplemented group by the ninth week of the experiment. There were no significant differences among treatments in any of the amino acids for either deproteinized blood plasma or rumen content. Deproteinized plasma threonine, valine, methionine, isoleucine, leucine, phenylalanine, and cystine levels decreased significantly for all animals with time, whereas glutamic acid increased. The concentration of each of the 17 rumen amino acids decreased significantly with time. Both groups of animals decreased in milk production more than expected. It is clear that a sulfur deficiency was produced in nine weeks on a practical diet. Since milk production, dry matter intake, plasma-free and rumen amino acid levels were not maintained in the sulfur-supplemented group of cows, it is concluded that the supplemental sulfur was either insufficient in quantity or inefficiently utilized.