ESTIMATION OF GENETIC TRENDS FOR ECONOMIC TRAITS IN CROSSBRED CATTLE BY USING REGRESSION METHODS

The present study was conducted on 782 crossbred cows sired by 35 bulls, maintained over the period from 1985 to 2009. The data were analyzed to estimate genetic, phenotypic and environmental changes in characters of economic importance which might have taken place during the several years of selective breeding practiced in the herd. The economic traits studied were first lactation milk yield, first lactation milk yield per day of lactation length and first lactation milk yield per day of calving interval in kg and age at first calving, first lactation length, first calving interval, first service period and first dry period in days. The average genetic changes in a given trait were estimated by four methods. Phenotypic trends were negligible for all the traits except age at first calving while, genetic trends were in desirable direction. Comparison of methods of estimation of genetic trend showed that adjustments for biases due to non-random allotment of dams with respect to their age and merit suggested by Powell and Freeman were useful for increasing the precision of the estimates. This method showed lower magnitude of standard error in comparison to other methods. Method-III showed lower standard error than method-IV. Hence, method –III was the best method of estimation of genetic trends.