The data analyzed were live weights of females (3475) of six genetic groups obtained by crossing red and white Holstein-Friesian (HVB) x Guzerá (Guz), with expected HVB gene fractions 1/4, ½ (F1) , 5/8 (from inter se mating), 3/4, 7/8 and > 31/32. The data were separately analyzed for 374 calves (up to age 120 d) and 524 heifers (121 to 550-d-old), using Proc Mixed of the SAS package, under a model including the fixed effects of genetic group (G), trimester of weighting and age within G as a co-variable, and animal as a random effect. An additive-dominant model was fitted to the daily gains including the individual breed additive difference (gI) (HVB-Guz) and heterosis (hI). In calves, the estimated gI was significant (P=0.059) but heterosis was not (P=0.92). Average daily gain for this category was 474 g/d in the ¼, 510 g/d in the ½ and from 575 to 610 g/d in the other four groups, with a linear trend on HVB gene fraction (gI = 0,171 ± 0,065 g/d), attributed to the observed fact that the calves with higher Bos indicus fraction did not adapt well to bucket feeding. This lower growth rate was compensated as heifers, category in which the F1 displayed the highest daily weight gain (371 g/d), which decreased from 309 g/d in the ¼ to 256 g/d in the >31/32 HVB. The additive-dominant model adequately fitted the daily gains in F1 and backcross heifers, but not in the 5/8 inter se cross, suggesting the a presence of epistasis. Excluding this last group, estimates were gI = -0,006 ± 0,023 and hI = 0,113 ± 0,020 g/d.
crossbreeding; dairy cattle; growth; heterosis; weight gain
