Effects of Different Fiber to Starch Ratios on Growth Performance, Nutrients Digestibility, and Ruminal Microbiota in Holstein Bulls

Abstract Background: The objective of this study was to investigate the effects of dietary neutral detergent fiber (NDF) to starch ratios on growth performance, nutrient digestibility, ruminal fermentation, and microbial community patterns. Thirty-six healthy Holstein bulls at nine months of age (averaged 282±37 kg of body weight) were randomly allocated into three treatments: dietary NDF to starch ratio of 1.13, 1.38, and 1.63. Dry matter (DM) intake (DMI), body weight gain, serum biochemical characteristics, hormones, total-tract digestibility, ruminal enzyme activities, ruminal fermentation, and microbial communities were analyzed.Results: Though the DMI and feed efficiency were not affected, the average daily gain (ADG) increased linearly with a decreasing NDF to starch ratio. DM digestibility, ruminal microbial diversity, ruminal amylase activity, propionate and butyrate concentration, serum glucose, acetyl-CoA carboxylase increased linearly with decreasing dietary NDF:starch ratio. The abundance of the predominant ruminal genus, Prevotella 1 (19.00%~31.64%) linearly decreased, while the proportion of two dominant genera (Ruminococcaceae NK4A214 group/4.14%~6.66% and Rikenellaceae RC9 group/5.57%~7.76%) increased with the decreasing NDF:starch ratio. Dry matter intake, digestibility of crude protein, ether extract (EE), NDF and ADF, AST, BUN, TP, NEFA, GH, IGF-1, and insulin were not affected by the dietary NDF:starch ratio.Conclusions: In conclusion, the dietary NDF:starch ratio of 1.13 benefits the weight gain of Holstein bulls. A potential reason might be the regulation of propionate productivity, amylase activity, and physiological metabolism through the change of dominant ruminal microbiota (Prevotella 1, Ruminococcaceae NK4A214 group and Rikenellaceae RC9 group), which might have a beneficial effect on the lipogenesis and body weight gain of Holstein bulls during the fattening period.