Effects of 2-methylbutyrate supplementation on growth performance and ruminal development in pre- and post-weaned dairy calves

The objective of this study was to evaluate the effects of 2-methylbutyrate supplementation on growth performance and rumen development in pre- and post-weaned dairy calves. Fifty-six Chinese Holstein male calves with 15days of age and 46.5±0.37kg of body weight (BW) were randomly assigned to one of four groups. The treatments were: control, low-2-methylbutyrate (LMB), moderate-2-methylbutyrate (MMB) and high-2-methylbutyrate (HMB) with 0, 3, 6 and 9g 2-methylbutyrate per calf per day, respectively. Supplemental 2-methylbutyrate was hand- mixed into milk in pre-weaned calves and the concentrate portion of post-weaned calves. The study lasted 75 days, including a 15-day adaptation period and followed by a 60-day sampling period. Calves were weaned at 60days of age. Six calves were chosen from each treatment at random and slaughtered at 30 and 90days of age. Body weight, dry matter (DM) intake and stomach weight were measured, samples of ruminal tissues and blood were determined. DM intake increased linearly (P<0.03) for post-weaned calves and overall DM intake with increasing 2-methylbutyrate supplementation and was higher for MMB and HMB than for LMB and control (P<0.05). Average daily gain (ADG) increased linearly (P<0.05) for pre-weaned calves, post-weaned calves and overall ADG with increasing 2-methylbutyrate supplementation, and was higher for MMB and HMB than for LMB and control (P<0.05). Total stomach weight for pre- and post-weaned calves increased linearly (P<0.05) and was higher for MMB and HMB than for LMB and control (P<0.05). The ratio of rumen weight to total stomach weight tended to increase linearly (P=0.055) for pre-weaned calves and increased linearly (P=0.019) for post-weaned calves, whereas the ratio of abomasum weight to total stomach weight decreased linearly (P<0.05) for pre-weaned calves and post-weaned calves with increasing 2-methylbutyrate supplementation. The ratio of total stomach weight to body weight for pre-weaned calves and post-weaned calves increased linearly (P<0.05) and was higher for MMB and HMB than for LMB and control (P<0.05). Both the length and width of rumen papillae, and the relative expression of mRNA for growth hormone receptor (GHR) and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) in rumen mucosa tended to increase linearly for pre-weaned calves, but increased linearly (P<0.05) for post-weaned calves and was higher for MMB and HMB than for LMB and control (P<0.05). Blood concentrations of BHBA increased linearly (P<0.05) for post-weaned calves with increasing 2-methylbutyrate supplementation and was higher for MMB and HMB than for LMB and control (P<0.05). Blood concentrations of GH and IGF-1 increased linearly (P<0.05) for pre- and post-weaned calves with increasing 2-methylbutyrate supplementation and was higher for MMB and HMB than for LMB and control (P<0.05). The present results indicated that 2-methylbutyrate accelerated growth of calves by improving rumen development and its ketogenesis. The 2-methylbutyrate stimulates the growth performance and rumen development of dairy calves in a dose-dependent manner. In the experimental conditions of this trial, the optimum 2-methylbutyrate dose was about 6.0g 2-methylbutyrate per calf per day.