The objective of this work was to evaluate the population structure of the sheep breed Santa Inês raised in Brazil. Pedigree data from 13,216 animals, belonging to 53 herds from eight Brazilian states, born between 1976 and 2010, were used. The program Endog was used for pedigree analysis and estimation of population parameters. From the total number of animals studied, 80.86% had a pedigree in the first ascendancy, 73.78% in the second, and 67.75% in the third. The maximum number of known generations was 19, and the average of equivalent generations was 4.67. The average generation interval was 3.22±1.77 years. The mean effective population size was of 172.5 animals. The number of founder animals was 829, but the effective number of founders was only 50. The 17 main ancestors accounted for 50% of the total genetic variability. The average relatedness coefficient was of 3.87% and the average inbreeding coefficient, of 6.92%. Despite the satisfactory average inbreeding coefficient in recent generations, this coefficient requires monitoring because of its proximity to the recommended limit. Gene flow among herds is the main factor for the increase of effective size and the maintenance of genetic variability in the breed Santa Inês.
ancestors; endogamy; founders; pedigree; genetic variability
