Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành y học dành cho các bạn tham khảo đề tài: Genetic parameters for first lactation dairy traits in Friesian, Montbéliarde and Normande breeds | I Génét. Sél. Evol. 1987 19 3 337-350 Genetic parameters for first lactation dairy traits in Friesian Montbéliarde and Normands breeds D. BOICHARD and B. BONAỈTI Station Génétique quantitative et ạppliquée . Centre de Recherches de Jouy F78350 Jouy-en-Josas. Summary Genetic parameters for dairy traits in first lactation milk yield fat and protein yields fat and protein contents were estimated in the 3 main French breeds by Henderson s method III. In the Normande and Montbeliarde breeds they were estimated from records including progeny of 291 and 219 young unproven bulls respectively whereas in the Friesian breed they were obtained from data of 342 young North American Holstein bulls used on pure European Friesian dams. Yields were expressed for a 305-day lactation length or multiplicatively coứected for lactation length according to the French evaluation system. Additional records of daughters of proven sires were included to improve the estimation of herd effects. Results were similar in the Normande and Montbéliarde and were consistent with the average literature data whereas in the Friesian breed heritability of fat content was very high In the 3 breeds genetic variability of protein content was about half that of fat content. The genetic antagonism with milk yield was stronger for protein content than for fat content. While the genetic correlation between fat yield and content was positive the corresponding correlation for protein traits seemed to be close to zero or even slightly negative. Correlations between yield of one component and content of the other also appeared to be negative. Accordingly if the selection goal is defined as maximising the useful yield while maintaining fat and protein content the selection criterion must include fat yield protein yield and protein content. Key words Dairy cattle genetic parameters protein yield protein content. Résumé Paramètres génétiques des caractères de production laitière en premiere lactation dans
