Arterial amino acid concentrations in sheep consuming forage diets

Arterial blood collected from sheep was analyzed for various amino acids to evaluate effects of dietary forage characteristics on adequacy of amino acid availability for protein synthesis. In three experiments with grass diets consumed Ž . ad libitum or in limited quantities by nearly mature wethers, differences in grass source and or quality generally did not Ž markedly affect arterial concentrations of essential amino acids. In the fourth experiment, wethers 7.5 months of age and . Ž . Ž . 31"0.8 kg BW consumed ad libitum bermudagrass Cynodon dactylon; BG and ryegrass Lolium multiflorum –wheat Ž . Triticum aestiÕum; RW hay mixtures in percentages of 0, 33, 67 and 100%. As DE intake decreased with increasing Ž dietary level of BG, arterial lysine concentration increased linearly Ps0.02; 116, 137, 144 and 157 mM for 0, 33, 67 and . 100% BG, respectively ; whereas, concentrations of other essential amino acids did not differ among treatments. In the fifth Ž . experiment, wethers 8.5 months of age and 33"0.9 kg BW consumed ad libitum BG or RW either coarsely chopped or finely ground and pelleted; DE intake was greater for RW vs. BG and for pelleted than for chopped grass. Lysine Ž . Ž . Ž concentration was greater Ps0.01 for BG than for RW and was decreased Ps0.03 by pelleting 133, 118, 114 and 78 . mM for chopped BG, pelleted BG, chopped RW and pelleted RW, respectively . Conversely, concentrations of tryptophan, Ž . valine, phenylalanine, isoleucine and leucine were greater P-0.03 for RW than for BG, and grinding and pelleting Ž . Ž . increased concentrations of valine Ps0.07 and phenylalanine Ps0.06 . In conclusion, DE intake with grass diets may influence particular amino acids most limiting to protein synthesis by growing ruminants, with lysine availability being of relatively greater concern with forages yielding high vs. low DE intake. q 1998 Elsevier Science B.V. All rights reserved.