Heritability and genetic trend for milk and fat yields in Holstein herds raised in the state of Rio Grande do Sul

Data comprising 5,007 records of first lactation of Holstein cows, daughters of 930 sires, from 33 herds in the state of Rio Grande do Sul, from 1984 to 1998, were used to estimate heritability coefficients and genetic trends for milk (MY) and fat (FY) yields and for fat percentage (%F). An animal model considered the genetic additive direct and residual as random effects and milking/ day number, herd and year/season of parturition, and cow age at parturition as fixed effects, linear and quadratic effects, as covariate, inn order to estimate the coefficients of heritability and to predict the breeding values (BVs) for MY, FY and %F. The genetic trend was estimated by the regression of mean annual animal BVs in relation to animal year birth. The averages and respective standard deviations for MY, FY and %F were: 6,862.80 +/- 1,881.21 kg/year, 228.63 +/- 78.01 kg/year and 3.32 +/- .18 %/year, respectively. The estimated coefficients of heritability and respective standard error for MY, FY and %F were: 0.30 +/- 0.008; 0.28 +/- 0.004 and 0.22 +/- 0.015, respectively. The estimated genetic correlations were: 0.85 +/- 0.19 and -0.15 +/- 0.17 for MY and FY and MY and F%, respectively. The genetic trend for MY was of 9.25 kg/year, 0.11 kg/year for FP and -0.07%/year for %F. The values estimated for the coefficients of heritability suggest that it is possible to increase the rates for genetic gain for MP and FP, without change on %F rate. The genetic gains for MY and FY were positive, but low, however they can be improved if breeding programs that stimulate the dairy man to increase both traits milk quality are implemented.