The effects of vitamin A on the beef quality, weight gain, and serum concentrations of thyroid hormones, insulin-like growth factor-I (IGF-I), and insulin in Japanese Black steers were investigated.Eight Japanese Black steers which were 14 months old were divided into two groups: high vitamin A group (H) and low vitamin A group (L). The animals in H were injected with 303 mg of vitamin A intramuscularly every month. All steers were given vitamin A added manifestation of clinical VA deficiency. Although there was no difference in feed intake between H and L, the average daily gain (ADG) in H was greater than that in L. The beef marbling in L was significantly better than that in H. The backfat depth in H was significantly thicker than that in L. The serum IGF-I concentrations in L gradually decreased and after the age of 18 months were significantly lower than those at the beginning of the experiment.The serum triiodothyronine concentrations in L were significantly lower than those in H during some periods. The change in the plasma glucose concentrations after the insulin injections (0.2U/kg body weight) was similar in H and L. The glucose infusions (0.2g/kg body weight) caused a marked increase in the plasma insulin concentrations in H and L, and both H and L showed similar areas under curves of plasma insulin levels which were above the basal levels. These results suggested that restricted vitamin A intake led to lower ADG, better beef marbling and lower serum IGF-I and triiodothyronine concentrations.

The effects of roughage levels on growth, beef quality, ruminal contents and serum constituents during the growing period in Japanese Black steers were investigated.Eight Japanese Black male calves, which were 4 months old, were divided into two groups: a high roughage group (H) and a low roughage group (L). The animals in H and L were fed a diet containing approximately 60% and 30% roughage on TDN basis respectively during the growing period (4 to 10 months old). They were fed the same diet in the fattening stage (11 to 30 months old). The average daily gain in L was greater than that in H during the growing period. The withers height and heart girth, however, were similar in both groups throughout this study. The body weights at the end of fattening period were also similar in both groups. The beef marbling in H was better than that in L, but not significantly. The intermuscular fat thickness in H was significantly thinner than that in L. These results suggest that feeding a large quantity of roughage during the growing period gives a preferable carcass for meat industry with relatively small amount of intermuscular fat.