Estimation of (co)variance components of nematode parasites resistance and somatic cell count in dairy sheep

Nematode parasites and mastitis are the major animal health constraints in sheep. The aim of this study was estimating the genetic (co)variances of nematode parasites resistance and somatic cell count in dairy sheep. From 2000 to 2008, Somatic Cell Score (SCS) and Faecal Egg Count (FEC) records were available on an experimental population consisting of 949 backcross ewes and 806 their daughters. Data were processed independently for each subpopulation in order to adjust for specific environmental effects and to obtain lactation records for both traits to be used in the genetic analysis. Variance components estimation was performed by using the REML method applied to a bi-trait repeatability animal model. Heritabilities of lactation SCS (LSCS) and FEC were 0.19 and 0.16. Genetic correlation was 0.21, whereas phenotypic correlation was 0.01. The estimated heritabilities confirm that both traits could be selected by the classical quantitative approach. The genetic correlation estimate between LSCS and FEC suggests that selection for one of the two traits would not have any detrimental effect on the other one.