Effects of fibrolytic enzymes and isobutyrate on ruminal fermentation, microbial enzyme activity and cellulolytic bacteria in pre- and post-weaning dairy calves

The objective of the present study was to evaluate the effects of fibrolytic enzymes (FE, containing 160 units of cellulase and 4000 units of xylanase) or isobutyrate (IB) supplementation on ruminal fermentation, microbial enzyme activity and cellulolytic bacteria in dairy calves. Forty-eight Holstein bull calves of 15 days of age and of 44.9 ± 0.28 kg of BW were randomly assigned to four groups in a 2 × 2 factorial arrangement. Two levels of FE (0 g (FE–) or 1.83 g per calf per day (FE+)) and IB (0 g (IB–) or 6 g per calf per day (IB+)) were added. Calves were weaned at 60-day-old and four calves were selected from each treatment at random and slaughtered at 45 and 90 days of age. There was no IB × FE interaction effect. Ruminal pH decreased with IB or FE supplementation for post-weaned calves, whereas concentrations of total volatile fatty acids and acetate increased with IB or FE supplementation for pre- and post-weaned calves. Acetate to propionate ratio increased with IB supplementation, but was unaffected by FE supplementation. Ammonia-N concentration decreased with IB or FE supplementation for pre- and post-weaned calves. For post-weaned calves, activities of CMCase increased with IB or FE supplementation, and activities of cellobiase, xylanase, pectinase, ß-amylase and protease increased with IB supplementation. Populations of B. fibrisolvens and F. succinogenes for pre- and post-weaned calves and R. flavefaciens for post-weaned calves increased with IB or FE supplementation. It is suggested that ruminal fermentation and growth performance of calves was improved with IB and FE supplementation, and the combination of IB and FE has the potential to stimulate the growth of pre- and post-weaned dairy calves.