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 cons umed 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, respe ctively) for 10 weeks to determine effects of dietary S on amino acid conce ntrations in ruminal fluid bacteria. The concentration of cysteine in bacte rial 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, di etary S did not alter methionine concentration in bacterial DM or total ami no acids, and for the few amino acids whose concentrations were affected, m agnitudes of change were relatively small. In conclusion, with diets modera te 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 bac teria of growing goats, which supports the contention that the primary pote ntial 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.