Tendencias genéticas y fenotípicas de características de crecimiento en el ganado Brahman de registro de México

The objectives of the present study were to calculate pheno-typic and genetic trend lines for birth weight (PN), and age corrected weaning weight (P205), yearling (P365) and at 550 days (P550). Weights of registered Brahman cattle in Mexico, years included 1993 to 2003, corresponded to the weights control program of the Mexican Association of Zebu Breeders (AMCC). The expected breeding values for genetic trends were estimated with the expected progeny differences (EPD's) from a previous study. Annual phenotypic trends were significantly (P<0.05), with the phenotypic change estimate for PN, P205, P365 and P550 of 0.142; 2.134; 8.759 and 12.820 kg/year, respectively. Annual direct genetic trends were significant (P<0.05) only for P205 and P550. Genetic change estimates was: 1 g/year for PN; 191 g/year for P205, 262 g/year for P365, and 608 g/year for P550. Genetic maternal trends were only significant (P<0.05) for P365 and P550. The estimates of the annual changes were 2.09^-6, -1.0, 13.0 and 36.0 g/year for PN, P205, P365 and P550, respectively. Both phenotypic and genetic direct annual trends seem to match with the PCDP implementation, mainly in postweaning traits. The annual change in the evaluated period has been positive but small. The use of breeding strategies based on expected progeny differences would increase significantly the possibility of higher genetic progress but using only phenotypic criteria.