Effects Of Isovalerate Acid On Digestive Enzymes Activities, Mucosal Histomorphology And Function Gene Expression Of Small Intestine In Dairy Calves

This study was conducted to evaluate the effect of isovalerate acid(Ⅳ) supplementation on s digestive enzymes activities, mucosal histo morphology and expression of its function gene of different growth period in Chinese Holstein bull calves. Thirty-six Holstein male calves(15-day-old) were chosen at similar birth-weight and divided into four groups randomly. The treatments were:control (without Ⅳ), LIV,3g/d (LIV) and HIV with 3,6 and 9 g IV per steer per day, respectively. Calves were slaughtered at 30,60 and 90 d. At slaughter the small intestine was removed and separated. Four parts of small intestine contents and mucosal tissues(including duodenal mucosal, proximal jejunal mucosal, distal jejunal mucosal and ileal mucosal) were collected to determine digestive enzymes activities, small intestine mucosal histomorphology and expression of its function gene. The results showed that, the length of duodenal, jejunal and ileal were increased with the isovalerate acid supplementation. Besides, wall thickness, mucosal thickness, villus length and the ratio of villus length to crypt depth were all increased with 6g/d and 9g/d supplemental isovalerate acid, while no significant differences were found in 6g/d group and 9g/d group(P> 0.05). In addition, digestive enzymes activities (lactase activities, amylase activities, trypsase activities and lipase activities) of small intestine contents were promoted by isovalerate acid supplementation, groups supplemented isovalerate acid(6g/d and 9g/d group) were higher than control group and 3mg/d group significantly (P< 0.05), while there is no significant differences between 6g/d group and 9g/d group (P> 0.05). Furthermore, the expression of GHR mRNA, INSR mRNA, IGF-1 mRNA, SGLT1 mRNA and Pep Tl mRNA were also enhanced by isovalerate acid supplementation. For 60 and 90-day-oldcalves, the abundance of GHR mRNA, INSR mRNA, IGF-1 mRNA, SGLT1 mRNA and Pep T1 mRNA of 6g/d group and 9g/d group were higher than control and 3mg/d group significantly (P< 0.05), while no significant differences were found in 6g/d group and 9g/d group (P> 0.05). However, for 30,60 and 90-day-oldcalves, the abundance of SGLT1 mRNA and Pep T1 mRNA of small intestine in 6g/d group were superior to control group and 3g/d group(P< 0.05). In summary, small intestine contents digestive enzymes activities, small intestine mucosal morphology and expression of its function gene were all promoted by supplemental isovalerate acid, and the optimum dose of isovalerate acid supplementation was 6mg/d.