Abstract
This study was conducted to compare a modified Logistic function adjusted for gestation effect with the ordinary Logistic function in respect to the goodness of fit, and to investigate the relationships between the growth curve parameters and reproductive performance. The modified Logistic function was yt=Aeλt'/(1.0+Be-kt) in which A, B, k, λ, t, and t'represented the estimated mature size, integration constant, rate of maturing, correction parameter, age in days, and a ratio of number of pregnant days at measuring to gestation length, respectively. The correction parameter meant relative growth rate of fetus, placenta, etc., to cow size. Body weight and eleven body measurements of 98 Japanese Black cows in Gifu Prefectural Livestock Station were used in this study. Individual size-age data were taken monthly from average 9.4 months up to 50.4 months of age. When the Logistic function with adjustment was used, the percentages of animals with more than 0.80 of adjusted coefficient of determination (adj R2) increased as compared with the ordinary Logistic function in all measurements. Furthermore in body length, chest width, pin bone width and cannon circumference, by using the ordinary Logistic function, a lot of animals who did not have the feasible iterative solution due to lack of convergence were observed, but the Logistic function with adjustment was fitted well in the size-age data of those animals with fewer exceptions. The average residual mean squares for body weight obtained by fitting the Logistic function with adjustment was improved from 434.22kg2 to 328.08 kg2. In the same manner, the average of adj R2 increased from 0.93 to 0.95. The improve- ment in the goodness of fit was also observed in chest girth, chest depth and body widths. The mature size estimated from the ordinary Logistic function was overestimated in comparison with those from the Logistic function with adjustment, while the rate of maturing was underestimated. The average rate of body weight fluctuation due to gestation at parturition was estimated at 9.96% of non-pregnant basal weight. For chest girth and body widths it ranged from 2.22 to 5.55%. The correlation coefficients between the growth curve parameters from the Logistic function with adjustment and reproductive performance were calculated after correcting for the effect of cow's birth place. The estimated mature body weight, chest girth and body widths had positive correlations with the average of calving interval (r=0.29-0.44) and negative with the number of calves born per productive year(r=-0.39--0.26).On the other hand, the rates of matuing were negatively correlated to the average of calving interval (r=-0.40--0.04). Further- more, the maturation rates of body widths in hind quarter tended to be positively correlated to the number of calves born per productive year (r=0.20-0.25).These relationships suggest that cows with larger size tend to have longer calving interval and fewer calves born per productive lifetime. In contrast cows with faster maturation rate show a tendency to shorter calving interval.
