RESUMO
Characterized as the most important gastrointestinal parasite (GIP) in the world, Haemonchus contortus is also the most predominant and pathogenic genus in Uruguay, causing high morbidity and mortality rates in sheep flocks. For approximately 26 years resistance to GIP has been included in the National Genetic Evaluation (NGE) of Corriedale and Merino breeds, using Faecal Egg Count (FEC) as the selection criterion. The aim of the present study was to estimate genetic parameters for FEC, post-weaning Body Weight (BW), Packed Cell Volume (PCV), FAMACHA© and Body Condition Score (BCS), to determine the possibility to include these traits in the NGE of GIP resistance and resilience, as complementary selection criteria and to investigate the sensitivity of breeding values to different environmental worm burden challenges. Data were collected on 19,510 lambs from 2000 to 2009 in 24 Corriedale studs that participated in the NGE of sheep in Uruguay. (Co)variances components were estimated using a multi-trait animal model performing a Bayesian analysis. Posterior means estimated for heritability (h2) were of low to moderate magnitude (between 0.10 and 0.33) for the traits analysed. Genetic correlations (rg) were not significantly different from zero for BW- Loge (FECâ¯+â¯100), BW-FAMACHA©, BW-PCV, Loge (FECâ¯+â¯100)-PCV, BCS-FAMACHA©, moderate favourable rg for Loge (FECâ¯+â¯100)-FAMACHA and PCV-BCS (0.55, 0.41) and high favourable rg for BW-BCS (0.66). These results indicate the possibility to complement selection programs incorporating BW, Loge (FECâ¯+â¯100), FAMACHA©, PCV and BCS in order to select resistant and resilient animal to GIP. Furthermore, genetic parameters for BW and Loge (FECâ¯+â¯100) to different environmental worm burden challenge was investigated. Two contemporary groups of low worm environment (Loge (FECâ¯+â¯100) below 6.40) and a high worm environment (Loge (FECâ¯+â¯100) above 6.75) were considered. In this model, h2 estimated for BW and Loge (FECâ¯+â¯100) were found to be not statistically different between low and high environmental worm burden, furthermore, high correlations between traits at both environments were also presented.
RESUMO
THE AIM OF THIS STUDY WAS TO INVESTIGATE THE GENETIC DIVERSITY WITHIN AND AMONG THREE BREEDS OF SHEEP: Corriedale, Merino and Creole. Sheep from the three breeds (Merino n = 110, Corriedale n = 108 and Creole n = 10) were genotyped using the Illumina Ovine SNP50 beadchip(®). Genetic diversity was evaluated by comparing the minor allele frequency (MAF) among breeds. Population structure and genetic differentiation were assessed using STRUCTURE software, principal component analysis (PCA) and fixation index (FST). Fixed markers (MAF = 0) that were different among breeds were identified as specific breed markers. Using a subset of 18,181 single nucleotide polymorphisms (SNPs), PCA and STUCTURE analysis were able to explain population stratification within breeds. Merino and Corriedale divergent lines showed high levels of polymorphism (89.4% and 86% of polymorphic SNPs, respectively) and moderate genetic differentiation (FST = 0.08) between them. In contrast, Creole had only 69% polymorphic SNPs and showed greater genetic differentiation from the other two breeds (FST = 0.17 for both breeds). Hence, a subset of molecular markers present in the OvineSNP50 is informative enough for breed assignment and population structure analysis of commercial and Creole breeds.