Abstract
Size-age data of 75 Japanese Black cows were analyzed to determine the most favorable model for description of live weight and withers height growth. Then, the relationships of growth parameters and estimated size for a cow with her reproductive performance and transmitting ability for preweaning performance were investigated. Reproductive performance includes age at first calving, average calving interval and number of calves produced per productive or lifetime year, and preweaning performance includes adjusted 180-day weight, withers height and weight, and withers height gain from birth to 180 days of age. Transmitting ability of a cow for preweaning performance was estimated by the best linear unbiased prediction (BLUP) procedure developed by HENDERSON (1973) and was expressed as expected progeny difference (EPD). Of five nonlinear growth models (Brody, Logistic, Gompertz, von Bertalanffy and Richards models), the Gompertz and Brody models were fitted best to the weight data of a cow. To withers height, all the five models were closely fitted. Judging from the values of residual mean squares and coefficients of determination, the Richards model was found to be most suitable for describing growth patterns of live weight and withers height in the cows. The Richards model, therefore, was used to make the following analyses. The estimates of growth parameters such as mature size (A), constant of integration (B), rate of maturing (K) and form parameter (M), which were calculated from the Richards model, had a generally low relationship with age at first calving, average calving interval and number of calves per productive year, although the estimates of B and M for body weight and the estimates of A for withers height had a significant negative cor relation with number of calves per lifetime year, (r=-0.336, -0.329 and -0.291) respectively.The estimates of A for withers height had a significant positive relation with EPD for adjusted 180-day weight (r=0.303). The estimates of growth parameters for body weight and withers height had no significant relationship with EPD for preweaning weight gain, withers height gain and adjusted 180-day height. The correlation coefficient between observed measurements of the cows and EPD for preweaning performance showed a considerable variation among months of age. A consistent significant relation was found between estimated body weight of cows at 6 to 48 months of age and EPD for preweaning weight gain and adjusted 180-day weight (range 0.312 to 0.525), respectively. Estimated withers height at 18 to 48 months had a significant pos itive relationship with EPD for adjusted 180-day withers height and withers height gain from birth to 90-days (range 0.316 to 0.370), respectively. Estimated body weight and withers height of cows at 6 to 48 months of age had no significant relationship with EPD for withers height gain from 90 to 180 days. These results suggest that size of cows has a positive relationship with EPD for preweaning performance and that the relationship becomes clearer when the size of cows is de termined from the Richards model.
