Genetic and phenotypic parameters for milk protein yields in Holstein cattle

Knowledge of genetic parameters is of paramount importance in designing sound breeding programmes. Genetic and phenotypic parameters are needed in the estimation of breeding values. The objectives of this study were to: estimate genetic parameters for milk, fat and protein yields; determine genetic and phenotypic correlations among these production traits and determine if genetic parameters are the same within lactations in Holstein cattle. A total of 17 598 Holstein 305 day milk records from the Zimbabwe Dairy Services Association were used to estimate heritabilities, variances, covariances and genetic and phenotypic correlations among 305 day yields of milk, fat and protein. The cows used were those that calved between 1994 and 1997 inclusive. This study was done in 1998. A FORTRAN iterative algorithm of REML — AIREML — (Gilmour, 1995) was used for the analyses. The animal model contained herd, year of calving, calving month, dry period, calving interval, milking frequency and animal effects. Heritability estimates for 305 day milk yield were 0.34 + 0.04; 0.22 + 0.06; 0.17 + 0.05; 0.10 + 0.05 and 0.09 + 0.04 for 1st, 2nd, 3rd, 4th and 5th and later lactations respectively. For fat yield corresponding estimates were 0.34 + 0.05; 0.33 + 0.07; 0.17 + 0.05; 0.09 + 0.06 and 0.10 + 0.06 respectively. Estimates for protein yield were 0.22 + 0.04; 0.25 + 0.07; 0.19 + 0.06; 0.07 + 0.05 and 0.12 + 0.05 for the respective lactations. Phenotypic correlations between milk and fat, milk and protein and fat and protein in 1st parity were 0.92, 0.95 and 0.92 respectively and for 2nd, 3rd, 4th and 5th and later parities they were 0.89, 0.97 and 0.92; 0.92, 0.98 and 0.94; 0.92, 0.98 and 0.94 and 0.93, 0.98 and 0.95 respectively. Genetic correlations were 0.92, 0.92 and 0.88; 0.86, 0.93 and 0.88; 0.83, 0.93 and 0.93; 0.46, 0.88 and 0.58; and 0.68, 0.89 and 0.83 for the respective lactations.

A research paper on genetic engineering in achieving higher milk yields in Zimbabwe.