Abomasal protein recovery and microbial protein synthesis in wethers fed high and low quality forage diets.

Four mature rumen and abomasal cannulated wethers were used in a 2 x 2 reversal experiment to study the effect of forage quality on daily quantity of abomasal protein and microbial protein synthesis. Diets were either high quality [HOo 16.4% crude protein (CP)] or low quality (LOo 9.3% CP) Coastal bermudagrass which provided 110.7 and 58.3 g CP intake daily, respectively. Non-ammonia CP reaching the abomasum daily was 99.6 g for HQ and 79.6 g for LQ, resulting in a 10% loss of CP from diet to the abomasum with the HQ diet. Conversely, there was a 36.5% gain in CP between the diet and abomasum with the LQ diet. The sulfur amino acids (methionine and cystine) were the only essential amino acids which were increased (P<.01) during rumen fermentation by the wethers fed the HQ diet. All individual essential amino acids, except arginine, and total essential amino acids were increased 2.0 to 2.5 times during passage of the LQ diet to the abomasum (P<.01). All nonessential amino acids, except proline, and total non-essential amino acids increased from the diet to the abomasum (P<.O1) with the low quality diet. Based on the recovery of diaminolSimelic acid from the abomasal digesta, microbial protein synthesized daily was 38.8 g on the HQ diet and 30.8 g on the LQ diet. Approximately 43.6 and 62.3% of the protein from the HQ and LQ bermudagrass diets, respectively, apparently escaped degradation in the rumen. (