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

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Abstract
One group of 12 cows received a concentrate mixture containing 0.10% S whereas the other similar group received the same concentrate mixture except supplemented with Na2SO4.10H2O to contain 0.18% S. Both groups of cows received the same corn silage (0.09% S dry basis) and the respective concentrate mixture ad libitum at a constant ratio of 6.3 to 1.0. Voluntary feed intake and milk production was significantly higher for the S supplemented group the 9th week. There was no difference between treatments for any of the deproteinized blood plasma or hydrolyzed rumen content amino acids. Free plasma threonine, valine, methionine, isoleucine, leucine, phenylalanine, and cystine and all 17 hydrolyzed rumen amino acids decreased significantly for all animals with time, whereas plasma glutamic acid increased significantly. A S deficiency was produced in 9 weeks on a practical diet. Since milk production, dry matter intake, plasma free and rumen amino acid levels were not maintained in the S supplemented group of cows it is concluded that the supplemental S was either insufficient in quantity or inefficiently utilized.