Genetic analysis of growth patterns of black and white dairy heifers

Monthly BW to 600 d of age along with BW at first calving of 743 heifers were analyzed to estimate the genetic relationship between BW at first calving and other growth variables. The Von Bertalanffy function and a two-phase logistic function were used to fit growth patterns of individual heifers. The two-phase logistic function fitted the data more adequately than did the Von Bertalanffy function. Calves from first parity dams were born at a lower degree of maturity than calves from third parity dams. Calves with a high proportion of Holstein genes had a higher BW both at first calving and at maturity. Heritabilities of the variables of the Von Bertalanffy and the two-phase logistic function ranged from 0.02 to 0.31 and 0.15 to 0.26, respectively. Estimated mature BW had a highly negative correlation with rate of maturation (-0.56 to -0.82); BW at first calving had a high genetic correlation (0.74 to 0.90) with estimated mature BW and a negative correlation with maturation rate (-0.18 to -0.40). Results of this study indicated that BW at first calving can be used as an indirect trait when mature BW is included in the breeding goal.