studies on dairy production of milking ewes. i. – estimates of genetic parameters for total milk composition and yield研究乳制品生产挤奶母羊。.pdf

Studies on dairy production of milking ewes I. - Estimates of genetic parameters for total milk composition and yield F. BARILLET D. BOICHARD LN.R.A., Station meliorationdaGénétique des Animaux, Toulouse, BP 27, F 31326 Castanet-Tolosan *)(LN.R.A., Station de Genetique quantitative et appliquee, F 78350 Jouy-en-Josas Summary Genetic parameters for dairy traits in first lactation (milk yield, fat and protein yields, fat and protein contents) were estimated from records of 1487 Lacaune ewe lambs born from 102 young rams undergoing progeny test and 74 proven rams. Variance and covariance components were estimated ENDERSONHS’ I III. by methods and According to the analysis, information from proven rams was totally or partially used for estimating fixed effects, or was excluded. Results appeared similar to the average literature data for dairy cows, except the correlation between fat and protein contents, which was rather high (0.8). The genetic standard deviation of fat was larger than that of protein, the ratio being about 1.3 for yields and 1.85 for contents. Accordingly, expected genetic change is likely to be smaller for protein matter than for fat matter. Whereas the genetic correlation between fat content and yield was positive, the genetic correlations between protein content and yield, or between content of one component and yield of the other, seemed to be close to zero and maybe negative. Accordingly, the selection criterion should include useful yield and content, instead of the useful yield alone. Useful yield (or content) was defined as a combination of fat and protein yields (or contents), with weighting I