Estrutura populacional da raça ovina Segureña e os efeitos da endogamia sobre características de crescimento.

Abstract

The goals of this thesis were to verify the conservation genetic status of the Segureño Spanish sheep breed and to evaluate the principal factors involved in the determination of growth traits in this breed. The data used n this study was provided by the Asociación Nacional de Criadores de Ovino Segureño – ANCOS, located in Granada province, Spain. The information about genetic variability and population structure were obtained using genealogical records from 37.459 animals registered between the years 1984 – 2007. To evaluate the inbreeding effects on growth traits, weight measurements taken between the years 1992 – 2007 were considered. The traits evaluated were: birth weight (BW), weight at 30 (W30), 45 (W45) and 75 (W75) days of age and also the average daily gains between 0-45 (ADG0-45), 0-75 (ADG0-75) and 45-75 (ADG45-75) days of age. The parameters used to evaluate the genetic diversity were: effective number of founders , effective number of ancestors , effective population size , inbreeding coefficient , average relatedness coefficient , generation interval , and the fixation indexes . To analyze the effect of the inbreeding on growth traits, were considered the individual inbreeding estimates and the environmental effects of sex, year-season-herd, birth type and age of the ewe. For the herds studied, a significant loss of genetic variability was not observed. The fixation indexes suggest that there is no population subdivision within the breed and the inbreeding level can be considered satisfactory for growth traits. Nucleus herds were not observed which may have contributed for the absence of within breed substructure. Among the environmental factors considered, the contemporary group (formed by individuals born in the same year-season-herd), the birth type and the sex of the lamb were the most important factors affecting the weights and average weight gains studied.