Effect of feeding rice whole crop silage on growth rate, levels of vitamin A, β‐carotene, vitamin E and IGF ‐1 in plasma and skeletal muscle protein degradation in Japanese black calves

This study evaluated the effects of rice whole crop silage ( RWCS ) on growth, plasma levels of vitamin A, β‐carotene, vitamin E and IGF ‐1, and expression of genes involved in muscle protein degradation and synthesis in Japanese Black calves. Eleven calves were divided into RWCS (fed RWCS ad libitum and concentrate, n  = 5) and control groups (fed hay ad libitum and concentrate, n  = 6). Final body weight and dairy gain were significantly larger in the RWCS group compared with the control group. Plasma β‐carotene and vitamin E concentrations were significantly higher in the RWCS group compared with control group. Although plasma vitamin E concentration in the RWCS group significantly increased from 4 to 9 months of age, it did not increase in the control group. At 6 months of age in the RWCS group, ubiquitin B ( p  <   0.05) and calpain 1 ( p  =   0.097) mRNA expression were lower than control group, but they were not different between groups at 9 months of age. These results indicate that RWCS increases plasma β‐carotene level and promotes muscle growth because of a decrease in the rate of protein degradation, but the effect is lost with the increase in plasma vitamin E level.