Effects of isovalerate supplementation on microbial status and rumen enzyme profile in steers fed on corn stover based diet

The objective of this study was to evaluate the effects of isovalerate supplementation on microbial status and ruminal enzyme activities in steers fed on corn stover based diet with a low proein. Eight ruminally cannulated Simmental steers were used in a replicated 4×4 Latin square experiment. The treatments were control (without isovalerate), LIV, MIV and HIV with 8.4, 16.8 and 25.2 g isovalerate per steer per day, respectively. Isovalerate was hand- mixed into the concentrate portion. Diet consisted of 60% corn stover and 40% concentrate (dry matter [DM] basis). Dry matter intake (averaged 9 kg/day) was restricted to a maximum of 90% of ad libitum intake. Whether direct counts, cultured using a roll-tube technique or real-time PCR quantification, population of total bacteria, cellulolytic bacteria and anaerobic fungi were linearly increased, whereas that of protozoa and total methanogens was linearly reduced with increasing isovalerate supplementation. Real-time PCR quantification of population of R. albus, R. Flavefaciens, B. Fibrisolvens and F. succinogenes was linearly increased (p<0.04) with increasing isovalerate supplementation. Activities of CMCase, xylanase and β-glucosidase were linearly increased (p<0.05), whereas that of protease was linearly reduced (p=0.005) with increasing isovalerate supplementation. Methane production was linearly decreased (p<0.001) with increasing isovalerate supplementation. Effective degradabilities of cellulose and hemicellulose of corn stover was linearly increased (p<0.001), whereas that of crude protein in diet was linearly decreased (p<0.001) with increasing isovalerate supplementation. The present results indicate that supplementation of diet with isovalerate improved microbial status and ruminal enzyme activities in steers. It was suggested that the isovalerate stimulated the digestive microorganisms or enzymes in a dose-dependent manner based on corn stover diet with a low protein. In the experimental conditions of this trial, the optimum isovalerate dose was about 16.8 g isovalerate per steer per day.