Population Structure and Genetic Variability of Angus and Nellore Herds

Reproductive isolation of cattle herds should have significant negative genetic consequences, including inbreeding depression and the loss of diversity through genetic drift. Cattle herds may also suffer detrimental effects on genetic variance caused by other demographic and population parameters such as effective population size, strong selection and founder effects. In the present study we use pedigree records to evaluate these potential impacts on a closed nucleus Angus from U.S. and an open multiplier Nellore herd from Brazil. The combined description of population structure and genetic variability of these two herds indicates that it is possible to maintain genetic variability with medium levels of inbreeding in herds with strong selection and small effective population size. Additionally, the analysis illustrates the importance of pedigree depth for accurately estimating population parameters, particularly, inbreeding and effective population size.