Genetic trends of Mexican zebu cattle populations

In Mexico, the genetic evaluations in Zebu breeds began in 2011 and there are no studies about the genetic progress achieved. Thus, this research aimed to quantify and analyse the genetic progress for growth traits in the Mexican Zebu beef cattle populations Nellore, Sardo Negro, Gyr, Indubrasil, and Guzerat. The genetic trends were obtained through weighted regression (by the number of animals) of estimated breeding values for direct birth weight, direct and maternal weaning weight, yearling weight, and weight at 540 days of age, on the year of birth. Genetic trends were also estimated by the four selection paths, groups of herds, and weighted averages of the sires' breeding values. The results showed genetic gain as expected of genetic improvement. Nellore presented the highest positive gains for all the traits, and Gyr had the smallest gains among the breeds. Guzerat showed contrary trends for weights until weaning, and had more favourable trends for weights after weaning than the other breeds. The genetic gains obtained for the growth traits reflected the strong influence of the selection made via the maternal paths. The results between weighted and unweighted average breeding values indicate no effective strategy for disseminating genetic material with high breeding values. The genetic gains obtained in the whole populations were due to the main groups of herds. Thus, to achieve further genetic progress, it is necessary to design a cooperative breeding program with a strategy for disseminating that genetic material.