Rumen Fermentation And Microbial Amino Acid Profile Influenced By Sources And Levels Of Feed Protein In Vitro

In this study, two experiments were designed to examine the effects of protein sources and levels on rumen fermentation and microbial amino acid (AA) profile in vitro in dual-flow continuous culturesystem.Experiment 1 was conducted to determine the effects of protein sources on rumen fermentation and AA profiles of rumen bacteria in vitro. Diets were formulated with isonitrogenous amounts of soybean meal, cottonseed meal, rapeseed meal, peanut meal, linseed meal or fishmeal; NDF were similar among the diets. The protein source did not significantly (PXU) alter pH values of the fermentation, but affect total VFA concentration and molar proportions, of acetate, propionate and butyrate(P<0.001), indicating the significant changes of fermentation type among treatments and virtually the alter of the proportion of microbial species present. There was a little difference (P<0.15) in efficiency of microbial protein synthesis among treatments, with the maximum for the soybean meal diet and the minimum for the peanut meal diet. Those differences may be attributed to the profile of AAs of protein sources essential to microbial synthesis. There were significant different in bacterial OM (P<0.03 ) and the proportion of AA-N (P<0.001) , but similar in bacterial N (p>0.2). All the essential AA (EAA) contents in the protein sources were lower than those of bacterial origins. EAA contents of bacterial protein, except lysine, cystine and tyrosine which had negative correlation with that of diets, however, appeared to be similar among the diets. Generally, AA profiles of rumen bacteria appear independent of the AA profiles of diets.Experiment 2 was performed to evaluate the effect of dietary protein levels on the rumen fermentation and AA profiles of rumen bacteria in virto. Diets were formulated with four levels of isolated soy protein (ISP) at the concentration of 0%, 33%, 67% and 100%; NDF contents were similar amount the diets. The result showed that pH values, concentrations of NH3-N and total VFA increased (Q; P<0.03) quadraticly with increased CP level of diets; so did individual VFA molar proportion (Q; P<0.03), with exception of isobutyrate. Based on the above rumen fermentation parameters, ISP levels at 33% and 67% were considered to be appropriate dietary treatments. Because of the deficency of available N source, the fermentation of 0% ISP treatment was much poor, and the fermentation pattern was different from others. As protein level in the diets increased, typical protein fermentation was observed: molar proportion of valerate, isobutyrate and isovalerate increased significantly, and 100% ISP treatment had the maximum. True digestibility of dietary DM, OM, CP and the efficiency of microbial synthesis showed significantly quadratic increase (Q; P<0.001). Increasing dietary protein levels resulted in similar (P>0.05) ratio of total EAA or non-essential AA to total AA of microbial proteins, but in changed microbial individual AA proportions (P<0.01), including those EAA of arginine, histidine, leucine, methionine, phenylalanine and threonine. With the increasing dietary CP levels, lysine contents appeared constantly; methionine appeared quadrticly decreased (Q; P<0.05); histidine and the branch-chain AA were quadraticly increased (Q; P<0.05). The AAs which concentration was lower in diets than in bacterial proteins may play a key role in regulation of rumen microbial protein synthesis.