Level of crude protein in concentrate supplements influenced rumen characteristics, microbial protein synthesis and digestibility in swamp buffaloes (Bubalus bubalis)

The objective of this research was to evaluate the effect of level of CP in concentrate on rumen fermentation, microbial population (bacteria, protozoa, and fungi), microbial protein synthesis, feed intake and feed digestibility in swamp buffaloes (Bubalus bubalis) fed on rice straw based diet. Four, rumen-fistulated 4-year old swamp buffaloes with 381 ± 10 kg liveweight were randomly assigned to receive four dietary treatments according to a 4 × 4 Latin square design. Four levels of crude protein (92, 124, 181 and 219 g/kg CP) in concentrate mixture were fed at 1 g/kg body weight (BW) and rice straw was fed ad libitum. The study revealed that dry matter intake, apparent digestibility of DM, OM, CP and NDF, were significantly higher in buffaloes fed with higher CP level especially at the 124-181 g/kg CP level, while, ADF digestibilities were not affected. Level of CP supplementation had affected on rumen pH, NH3N and blood urea N (P < 0.01). Meanwhile, rumen propionic acid production was significantly higher at 181 g/kg CP level, while total fatty acids (VFA), acetic acid, butylic acid and C2:C3 ratio, were similar among treatments. However, protozoal and fungal zoospore populations were not changed while bacterial populations were significantly different among treatments and were higher with high level of CP. Furthermore, application of quantitative PCR to quantify predominant cellulolytic bacteria (16S rRNA) targets revealed that treatments did not change population of Ruminococcus flavefaciens bacteria (P > 0.05) and methanogenic bacteria (P > 0.05). Meanwhile, total bacteria (P < 0.05), Fibrobacter succinogenes (P < 0.05) and Ruminococcus albus (P < 0.01) population were significantly increased when CP was at a higher level. Moreover, PD excretion, PD absorption, N absorption, N retention, MNS and EMPS were significantly increased. Therefore, based on this study, it could be concluded that level of CP between 124 and 181 g/kg CP in the concentrate supplement revealed the highest rumen fermentation efficiency in swamp buffaloes fed on rice straw.