RELATIONSHIP BETWEEN DAILY MILK-YIELD AND PERSISTENCY OF HUNGARIAN HOLSTEIN-FRIESIAN THROUGH SELECTION INDEX AND SUB-INDEXES

Multiple Trait Derivative Free Restricted Maximum Likelihood procedure s were used to analyse the relationships between persistency and daily milk yield performance. Genetic and phenotypic (co)variances were gen erated from this analysis to construct full and reduced selection indi ces, selection sub-indices and reduced selection sub-indices. The stru cture of the data consisted of 281 half-sib families and the lactation records in each group ranged between 12-24 records. The expected gene tic gain in daily milk yield by selection sub-indices was similar to t he corresponding value calculated by selection index, so the breeder c an use a selection sub-index in the breeding program to improve daily milk yield. The contribution of persistency to improvement in daily mi lk yield was higher by sub-index than selection index application. The highest improvement of persistency was associated with the maximum im provement in daily milk yield per lactation and per calving interval a nd was achieved by a selection index which involved all these traits.