Genetic parameters and breeding values for productive reproductive and persistency of milk yield traits of culled cows and their contemporaries retained in herd of friesian cattle at different lactations.

Records of production, reproductive and persistency of milk yield performance of Holstein Friesian cows kept at Mezoheges State Farm, Hungary collected during the period from 1982 to 1990 were used. These were either culled after completing a particular lactation (n = 2219) or retained to give subsequent lactations up to the 4. h lactation, (n = 4138). Data were analysed to estimate genetic parameters breeding values and to compare the productive and reproductive performance between the two groups. The data covered milk production traits: total milk yield (TMY), 305-day milk yield (305-d MY), 305-day fat yield (305-d FY) and persistency of milk yield (Pr MY) and reproductive traits: number of services per conception (NSC) and days open (DO). The results obtained could be summarized as follows: -The actual means of TMY, 305-d MY, 305-d FY, Pr MY, NSC and DO were 7197, 6974,255 kg, 72.71%, 2.23 services and 125.8 day, respectively, across 1. t four lactations. Coefficients of variation (CV%) of milk production traits ranged from 25.08 to 34.00%, but for Pr MY was 13.45%, while for NSC and DO were 73.99 and 63.56%, respectively. -The estimates of heritability ± S.E of the 1. t lactation based on animal model method for TMY, 305-d MY, 305-d FY, Pr MY, NSC and DO were 0.31± 0.05, 0.35 :t. 0.05,0.30± 0.04,0.10± 0.03,0.12 ±. 0.03 and 0.09± 0.03, respectively. -Estimates of rg and r p correlations between production and reproduction traits were positive and medium to high ranged from 0.58±0.12 to 0.91±0.05 and from 0.24 to 0.50, respectively. Also estimates of rg correlation between Pr MY and each of NSC and DO were 0.21±0.15 and 0.12±0.11, while rp were 0.07 and 0.08, respectivel. _ Culling rate increased with advance of parity,being 26.3 and 49.2 % at the end of the 1. t and 4. h lactations, respectively . Culled cows had significantly higher TMY, 305-d My, 305-dFY and Pr MY than those retained and the differences between the two groups were generally more pronounced in the 1. t two lactations. Culled cows had also significant larger NSC and longer DO than retained cows. These results showed that the culled cows have lower reproductive performance and higher milk production traits than those retained in the herd.- The range in estimates of breeding values of animals for all traits studied for both retained and culled cows was wide, suggesting that there is scope for selection.-The results indicated that more attention should be given to high yielding cows, particularly their reproductive management, to increase their longevity and hence improve herd productivity. Moreover, culling decisions have an important influence on the economic performance of the dairy but are must be based on the EBVs for economic traits.