Abstract
In order to clarify the vitamin A restriction on the meat productivity of Japanese black steers, two experiments, each with eight Japanese black steers (first experiment : 10 months old, second experiment : 15 months old), were conducted. The vitamin A supplied group (VAS) was fed rice straw and concentrate supplemented with 4,800 IU/kg ad libitum. The vitamin A restricted group (VAR) was given free access to rice straw and concentrate supplemented with no vitamin A. The TDN and DCP contents of two concentrates were equal. After the plasma vitamin A of VAR steers decreased to below 40 IU/dl, the steers were slaughtered together with another pair of VAS. There were no differences in the daily gain, feed intake between the VAR and VAS. The rib eye area and yield estimated percentage of VAR was significantly higher than of VAS. There were no differences in BMS and BCS numbers between the two groups. The muscle percentage in the carcass was higher in VAR than in VAS, and the fat percentage in VAR was lower than in VAS. The omental fat weight of VAR was significantly higher than of VAS but there were no differences in mesenteric fat, digestive tract, liver and heart weight. The fat content and meat color of longissimus dorsi in VAR was not different from in VAS. Growth hormone response to the growth hormone releasing factor infusion tended to be smaller in VAR than in VAS. The results indicate that restriction of vitamin A decrease carcass fatness and increase carcass leanness.
