Abstract
Nineteen thousand and thirty registered Japanese black breeding cows in Miyazaki were investigated in order to clarify the effects of same factors on the gestation length and the weight gain per day at the auction of calves (WGD), and also to determine the relationships between these two traits. The region effects significantly affected to the gestation length and WGD. It was shown that the WGD tended to increase with following to the parity. The effects of the age of the first insemination were found significantly on the gestation length (p<0.01) and the WGD (p<0.05) with use of heifer' s data. The suitable age for the first insemination was 13-14 months for obtaining well gestation length and calf' s growth rate. The WGD tended to increase according to the gestation length.
