Population structure and genetic variability of brazilian Quarter horse

The Quarter Horse race (Q) appeared in Brazil in 1955, was presented as versatile to working in farm and racing. The aim of the study was to assess the population structure and genetic variability of QH breed in Brazil. The pedigree information was from Brazilian association of Quarter Horse breeders (ABQM). The data used involve records of 121,444 animals (47% male), born between 1950 and 2008. The analyzes were performed with SAS and ENDOG software. The maximum value of registered animals (5.4%) occurred in 2007. The average number of progeny was 14.1 per stallion and 4.2 per mares, with generation interval (GI) of 9.3 years. The completeness (C) of the pedigree was 83% calculated for the total population and 100% for animals born after 2000. The effective number of founders (fe), ancestors (fa) and founder genomes (fg) was 333,330 and 306, respectively. The genetic variability of the QH breed was explained by 7,254 ancestors, 50% of the variability explained by 161 ancestors. The observed values of the average number of progenies are consistent with the averages indicated in other breeds of horses. The high value of GI indicates loss of annual genetic gain and lack of orientation on the appropriate use of the breeding, therefore, be improved with purpose of get best indexes. The value of C indicates attention and importance by the technical quality of the genealogical information of the register book. The values of the probability of gene origin (fe, fa and fg) is low based on the total number of animals studied, but the tracking and monitoring of genetic variability must be continuous. When compared, the values of probability gene origin indicate that the founders (fe) remain more in the herd as ancestors (fa) and founding genes (fg), indicating maintenance of the founding lineages of breed in Brazil. The totality of genetic variability, measured by the number and percentage of ancestors, show greater genetic variability and more ancestors in the formation of the QH population compared to other breeds of horses. Although it is not worrying, low genetic variability of the Quarter Horse breed in Brazil was observed, suggesting warning to breeders for use more animals as breeding stock.