Estimating degradation of individual essential amino acids in fish meal and blood meal by rumen microbes in a dual-flow continuous-culture system

Current feeding systems are based on the assumption that the AA profile of rumen undegraded protein is similar to that of the original feed. The objective of this experiment was to determine rumen bacterial degradation of individual essential AA in fish meal (FM) and blood meal (BM). Eight dual-flow continuous-culture fermentors were used in a completely randomized block design with a factorial arrangement of treatments and 3 replicated periods. Fermentors were supplied with 95 g of dry matter/d of isonitrogenous diets. Treatments contained a nonprotein N source (urea and tryptone) that was substituted with increasing proportions of FM or BM (0, 33, 67, or 100%). Diets consisted of 22.0% crude protein, 35.2% neutral detergent fiber, 34.6% nonfiber carbohydrates, 2.0% ether extract, and 9.2% ash. We hypothesized that the increase in the flow of individual AA would be attributed to the increase in the supply of the AA from each protein supplement. True organic matter degradation was decreased by increasing levels of FM or BM, but did not affect degradation of neutral detergent fiber and acid detergent fiber, total volatile fatty acids (VFA) concentration, or the molar proportion of propionate. There was a substrate by level of inclusion interaction in acetate molar proportion and branched-chain VFA. Butyrate concentration decreased linearly with increasing levels of FM and BM in treatment. Changes in branched-chain VFA reflected differences in content of branched-chain AA between supplements and the level of inclusion, although the quadratic effect suggests that other factors were involved. Ammonia-N concentration showed a substrate by level of inclusion interaction. Total dietary N and AA flows increased with increasing levels of FM or BM in treatment. The efficiency of bacterial crude protein synthesis was not affected by treatment, but the flow of bacterial N decreased in FM diets as the level of FM increased. Flows of AA increased linearly with increasing levels of the respective AA from supplements. Arginine, Ile, Met and Phe were more degradable, while His was more resistant to bacterial degradation. Results suggest that the resistance to rumen bacterial degradation of individual AA varies within FM and BM protein and may affect the estimates of dietary supply of individual AA to the small intestine.