GENETIC-PARAMETERS FOR MILK-YIELD AND COMPOSITION OF CROSSBRED DAIRY-CATTLE IN BRAZIL

Data representing 20 dairy herds in Brazil from 1981 through 1992 were collected for study. After screening, 1430 to 2343 lactation records by 955 to 1402 cows were analyzed to estimate effects influencing milk , fat and protein yields and fat and protein percentages, Data represe nted total and 305 day performance. Animals were crossbreds, represent ing groups of daughters by 80 crossbred sires. Sires were from 5/8 to 7/8 European-Zebu crossbreds; daughters ranged from 2/8 to 7/8. Europe an contribution was mostly Holstein; Zebu contribution was Gir and Guz era. Within crossbred groups, heritabilities ranged from 0.10 to 0.24, if records were not adjusted for days in milk, close to classic estim ates for yields from temperate climates but lower than those for perce ntages. Heritabilities were slightly but consistently lower for 305 da y records than for total records. Adjustment for days in milk lowered heritabilities to 0.06 to 0.22. Genetic correlations between total and 305 day performance were high, 0.84 to 1.00 (10 estimates); phenotypi c correlations ranged from 0.52 to 0.99. Other estimates pooled within the crossbred groups were similar to those obtained in purebred group s within temperate areas. Estimates of genetic change from selection w ithin crossbred groups would not be expected to differ widely from est imates obtained elsewhere for purebreds.