Sulfur, Nitrogen, and Amino Acid Balance, and Digestibility of Low-Sulfur and Sulfur-Supplemented Diets Fed to Lactating Cows

Abstract

Eight mature lactating Holstein cows were divided into two groups. The low-sulfur group received a concentrate mix containing 0.10% sulfur and the sulfur-supplemented group received the same concentrate mix containing 0.18% sulfur. Both groups were fed the same corn silage (0.09% sulfur, dry basis) and the respective concentrate mix ad libitum at a ratio of 6.3 to 1.0. Eighty per cent of the ad libitum intake was fed during the balance and digestibility trials. The low-sulfur group excreted significantly less sulfur in urine but not in feces or milk. All cows were in negative sulfur and nitrogen balance. The supplemental sulfur was inefficiently utilized, as indicated by the increased urinary excretion of sulfur and by no effect on sulfur balance. Apparently, inorganic sulfur only partially met the cow's total dietary sulfur requirement. Balance of amino acids was very similar for both groups. All animals were essentially in balance for methionine, cystine, and tyrosine, negative balance for glutamic acid and lysine, and in positive balance for histidine, arginine, aspartic acid, threonine, serine, glycine, alanine, valine, isoleucine, leucine, phenylalanine, and proline. There was a positive balance of both essential and nonessential amino acids as two separate groups.