Genetic basis and inbreeding in the Brazilian Guzerat (Bos indicus) subpopulation selected for milk production

The Guzerat breed is well adapted to the tropical conditions of Brazil. After 1940, the widespread use of Guzerat cattle for crossing has reduced its population size. In 1994, a selection program for milk production traits was initiated in some purebred herds. However, its success is compromised by genetic drift and an increased inbreeding coefficient (F). The objective of this study was to evaluate the genetic status of the Guzerat population under selection for milk production in order to monitor genetic variability. Genealogical data from 10,051 animals were used to estimate genetic parameters. The average F for all animals and for inbred animals in the pedigree was 0.009 and 0.025, respectively. Average relatedness was 0.011. The average generation interval was 7.48 years and the linear increase in F per generation was 0.0051. There was no trend of changes in the effective population size along generations, with the observation of an effective size of 98 in the last generation evaluated. The effective number of founders and ancestors was 318 and 101, respectively. Only 47 of 2106 ancestors contributed to 50% of the reference population. The bottleneck effect was 3.15. Average F and relatedness values are still low despite non-random mating. However, the reduced effective population size and effective number of ancestors indicate a risk of an increase in the inbreeding coefficient and genetic drift and consequent loss of variability.