Abstract
Using genetic and phenotypic parameters of age at first mating (AFM), age at first calving (AFC), Ist total milk yield (MT) and Ist total fat yield (FY), from data on 1451 Holstein Friesian cows of 268 sires, the following 4 selection indices were constructed : multi-trait selection index I-1: involved all traits; restricted selection indices; I-2: restriction on AFM and AFC; I-3: restriction on AFC, and I-4: restriction on AFM. All fixed effects (herd-year-month of calving) and random effect (genetic sires group) were adjusted by Restricted Maximum Likelihood Procedure. AFM and AFC accounted for 1.69% and 25.19% of variation in MY and 1.59% and 23.33% in FY respectively. Heritabilities of AFM, AFC, MY, and FY were 0.310+/-0.103, 0.311+/-0.110, 0.246+/-0.111 and 0.348+/-0.093 in the same order. Non significant negative genetic correlations were obtained between AFC with MY and FY (-0.067+/-0.097 and -0.116+/-0.162) and AFM with MY and FT (-0.035+/-0.099 and -0.045+/-0.166), and significant positive genetic correlations observed between AFM and AFC (0.968+/-0.010) and between MY and FY (0.324+/-0.104). The highest estimate of phenotypic correlations occured between MY and FY (0.633+/-0.111) and between AFC and AFM (0.950+/-0.110). Restricted selection index I-3 gave the maximum predicted genetic progress per generation for MY and AFM (139.27 kg and -0.58 month resp.), while I-4 gave the maximum predicted progress for FY and AFC (7.05 kg and -0.52 month resp.). The accuracies of the indices I-1, I-2, I-3 and I-4 were 27, 24, 64, and 51% resp. The relative economic values of the traits are given as well as correlations of breeding values for individual traits with the overall index. One unit change of any index gaves change in MY and FY ranged between 12.08 to 12.64 kg and 0.61 to 0.74 kg respectively.