Plasma amino acid profiles and growth of the bovine fed different sources of nitrogen and levels of sulfur.

One-hundred-twenty calves were utilized in a 2 X 3 factorial design experiment of 140 days to determine the effects of dietary urea (U) or soybean meal (SBM) with added sulfur (S) plus corn silage on growth and plasma constituents. Total dietary crude protein (CP) of SBM-supplemented diets averaged 9.06%, and U-supplemented diets averaged 9.16% CP. Within each nitrogen source, S was added to supplements to provide 0.0, 0.15, or 0.30% added S based upon predicted intake. Calves fed SBM-supplemented diets had higher (P less than 0.05) gains and lower (P less than .05) plasma urea nitrogen levels compared to calves fed U-supplemented diets. The addition of S to SBM-supplemented diets did not significantly affect growth, efficiency or plasma nitrogen constituents. Calves fed the U-supplemented diets with added S had higher (P less than .10) gains and a trend toward improved efficiency compared with those supplemented with no added S. On day 28 plasma aspartic acid, threonine, serine, glutamic acid, glycine, methionine, total nonessential and total amino acid concentrations were increased (P less than .01 to P less than .10) by the addition of S to U-supplemented diets compared to the basal U diet. Isoleucine was higher (P less than .05) in calves fed SBM-supplemented diets compared to those fed U-supplemented diets. On day 140 higher (P less than .05) plasma threonine, valine, isoleucine, leucine, phenylalanine, lysine and total essential amino acids were observed in calves fed SBM compared to U-supplemented diets.(ABSTRACT TRUNCATED AT 250 WORDS)