Effects of dietary sulfur level on amino acid concentrations in ruminal bacteria of goats

12 Angora (18+/-0.6 kg BW) and 20 Alpine (24+/-1.0 kg BW) goat wethers consumed diets (14.3% CP and 1.67-1.80 Mcal/kg ME, DM basis) with 0.11, 0.20, 0.28 or 0.38% S (supplemental S : CaSO4; N:S ratio is 21, 12, 8 and 6, respectively) for 10 weeks to determine effects of dietary S on amino acid concentrations in ruminal fluid bacteria. The concentration of cysteine in bacterial DM changed quadratically (P<0.08) as dietary S increased (3.28, 3.77, 3.80 and 3.65% for 0.11, 0,20, 0.28 and 0,38% S, respectively). However, dietary S did not alter methionine concentration in bacterial DM or total amino acids, and for the few amino acids whose concentrations were affected, magnitudes of change were relatively small. In conclusion, with diets moderate to low in ME, levels of S greater than 0.20% and N:S ratios less than 12:1 had very little effect on amino acid concentrations in ruminal fluid bacteria of growing goats, which supports the contention that the primary potential influence of inorganic dietary S on absorbed S-containing amino acids is through the quantity of microbial protein synthesized in the rumen. (C) 2000 Elsevier Science B.V. All rights reserved.