Genetic parameters for body weight, worm resistance, packed cell volume and FAMACHA© under natural infection in Corriedale sheep

Gastrointestinal parasites (GIP) are one of the main constraints for sheep production worldwide. In Uruguay, the most prevalent and pathogenic parasite is Haemonchus contortus. One approach to control parasite infection is to select genetically resistant animals into a breeding program. Faecal egg count (FEC) is the criterion mostly used to evaluate genetic resistance to GIP, although there are alternative indicators that could be used. The aim of the present study was to estimate genetic parameters for body weight, FEC, packed cell volume (PCV) and FAMACHA© score. To determine the possibility to include these traits in the genetic evaluation of GIP resistance, as complementary selection criteria to FEC. Data from 15,073 post-weaned lambs, the offspring of 343 rams, were recorded during a 16-year period from 2000 to 2015, from Uruguayan Corriedale stud flocks. A Bayesian analysis was performed to estimate genetic parameters, using a multivariate animal model including post-weaning body weight (BW), FEC, PCV and FAMACHA©. Heritabilities for these traits were of low to moderate magnitude (0.14 to 0.35). Genetic correlations (rg) were close to zero for FAMACHA©-BW, low but favourable for FEC-BW (-0.12) and for FEC-PCV (-0.23), and moderate to high between PCV-BW, PCV-FAMACHA© and FEC-FAMACHA© (0.54-0.73). The high rg between FEC-FAMACHA© estimated in the present study, indicate the possibility to complement both traits in order to select resistant and resilient animal to GIP. There would be an improvement not only at a genetic level but also for the environment and it would curb help to lead with the problematic situation of anthelmintic resistance.