The present study evaluated the effects of isovalerate supplementation on the development of the small intestinal mucosa in dairy calves. Forty-eight Chinese Holstein bull calves at 15 days of age and 45.1 ± 0.36 kg of body weight were assigned randomly to four groups. The treatments were control, low-isovalerate, moderate-isovalerate and high-isovalerate with 0, 3, 6 and 9 g isovalerate per calf per day, respectively. The study comprised 75 days with a 15-day adaptation period followed by a 60-day sampling period. Calves were weaned at 60 days of age. Six calves were chosen from each treatment at random and slaughtered at 30 and 90 days of age. The small intestine morphology and activities of amylase and trypsin improved significantly with increasing age. No interaction between treatments and age was observed. The small intestine length, mucosa layer thickness, villus height and crypt depth increased linearly with increasing isovalerate supplementation. However, the ratio of villus height to crypt depth was not affected by treatment. Activities of amylase and trypsin increased linearly. The lactase activity increased linearly during the 75-day period and for pre-weaned calves but was unaltered for post-weaned calves. The relative mRNA expressions of growth hormone receptor, insulin-like growth factor-1 receptor and sodium-glucose co-transporter-1 in the small intestine mucosa increased linearly, and a similar pattern was observed for the expression of peptide transporter-1 in the duodenum and proximal jejunum. The results suggested that small intestine development was promoted by isovalerate in a dose-dependent manner.

Isovalerate supplements could stimulate rumen development by improving morphology and function of rumen mucosa, and then promote the growth of calves. This study was done to evaluate the effects of isovalerate supplements on morphology and functional gene expression of rumen mucosa in dairy calves. In total, 48 Chinese Holstein male calves with 15 days of age and 45.1±0.36 kg of BW were randomly assigned to four groups. The treatments were: control, low-isovalerate, moderate-isovalerate and high-isovalerate with 0, 3, 6 and 9 g isovalerate per calf per day, respectively. Supplementary isovalerate was hand-mixed into milk in pre-weaning calves and into concentrate portion in post-weaning calves. The study consisted of a 15-day-adaptation period and a 60-day-sampling period. Calves were weaned at 60 days of age. Three calves were slaughtered from each of the four treatments at 30, 60 and 90 days of age. The weight of body and stomach were measured, samples of ruminal tissues and blood were analyzed. Total stomach weight, total stomach to BW ratio, rumen wall and keratinized layer thickness, serum growth hormone and IGF-1 for both pre- and post-weaning calves increased linearly with increasing isovalerate supplements. Rumen to total stomach weight ratio, the length and width of rumen papillae, and serum β-hydroxybutyrate increased linearly for post-weaning calves. However, abomasum weight to total stomach weight ratio decreased linearly for both pre- and post-weaning calves. The relative messenger RNA expression for growth hormone receptor, IGF-1 receptor and 3-hydroxy-3-methylglutaryl-CoA synthase 1 in rumen mucosa increased linearly for post-weaning calves. Our results suggested that isovalerate supplements promoted rumen development in a dose-dependent manner. The optimum dose was 6.0 g isovalerate per calf per day.