Structure and genetic diversity of Brazilian Zebu cattle breeds assessed by pedigree analysis

The monitoring of population structure, inbreeding and other related parameters has great potential to prevent major losses of genetic diversity in populations of Zebu cattle in Brazil. Therefore, the objective of the present study was to investigate the structure and genetic diversity of Brazilian Zebu cattle breeds by pedigree analysis. The national pedigree file of the seven Brazilian Zebu breeds was used, which included all registered animals (12,290,243) born between 1938 and 2012: Brahman, Gir, Guzerá, Indubrasil, Nelore, Sindi, and Tabapuã. Almost all breeds studied undergo expansion in their census which, however, is not accompanied by the maintenance of genetic diversity. Problems were encountered in all breeds, but most of them can currently be considered less important. Using the calculation method considered as the most accurate for pedigree analysis when some population substructure exists, all breeds, except Sindi, had effective population size greater than 100. The most common problems were the presence of tight bottlenecks in the pedigree, which were mainly due to the intensive use of few animals as parents and the high degree of population subdivision. The use of a wider range of sires is therefore recommended. However, most Zebu breeds can deal with breeding programs using high selection intensities. Greater care should be taken in the case of the Indubrasil breed since its census was reduced drastically over the last few years, a fact favoring the occurrence of serious problems related to inbreeding. Although Sindi presents problems due to subdivision and possesses a relatively small census compared to other Zebu breeds, this population would have a promising future if its breeding policy were revised.