SELECTION INDEXES FOR IMPROVEMENT MILK AND FAT YIELD BASED ON AGE AT FIRST MATING AND CALVING UNDER HUNGARIAN CONDITIONS

Using genetic and phenotypic parameters of age at first mating (AFM), age at first calving (AFC), Ist total milk yield (MT) and Ist total fa t yield (FY), from data on 1451 Holstein Friesian cows of 268 sires, t he following 4 selection indices were constructed : multi-trait select ion index I-1: involved all traits; restricted selection indices; I-2: restriction on AFM and AFC; I-3: restriction on AFC, and I-4: restric tion on AFM. All fixed effects (herd-year-month of calving) and random effect (genetic sires group) were adjusted by Restricted Maximum Like lihood Procedure. AFM and AFC accounted for 1.69% and 25.19% of variat ion in MY and 1.59% and 23.33% in FY respectively. Heritabilities of A FM, AFC, MY, and FY were 0.310+/-0.103, 0.311+/-0.110, 0.246+/-0.111 a nd 0.348+/-0.093 in the same order. Non significant negative genetic c orrelations were obtained between AFC with MY and FY (-0.067+/-0.097 a nd -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 betwee n AFM and AFC (0.968+/-0.010) and between MY and FY (0.324+/-0.104). T he 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 g eneration 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 tr aits 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 res pectively.