Genetic analysis for mastitis resistance and milk somatic cell score in French Lacaune dairy sheep

Genetic analysis for mastitis resistance was studied from two data sets. Fi rstly, risk factors for different mastitis traits, i.e. culling due to clin ical or chronic mastitis and subclinical mastitis predicted from somatic ce ll count (SCC), were explored using data from 957 first lactation Lacaune e wes of an experimental INRA flock composed of two divergent lines for milk yield. Secondly, genetic parameters for SCC were estimated from 5272 first lactation Lacaune ewes recorded among 38 flocks, using an animal model. In the experimental flock, the frequency of culling due to clinical mastitis ( 5%) was lower than that of subclinical mastitis (10%) predicted from SCC. P redicted subclinical mastitis was unfavourably associated with the milk yie ld level. Such an antagonism was not detected for clinical mastitis, which could result, to some extent, from its low frequency or from the limited am ount of data. In practice, however, selection for mastitis resistance could be limited in a first approach to selection against subclinical mastitis u sing SCC. The heritability estimate of SCC was 0.15 for the lactation mean trait and varied from 0.04 to 0.12 from the first to the fifth test-day. Th e genetic correlation between lactation SCC and milk yield was slightly pos itive (0.15) but showed a strong evolution during lactation, i.e. from favo urable (-0.48) to antagonistic (0.27). On a lactation basis, our results su ggest that selection for mastitis resistance based on SCC is feasible. Patt erns for genetic parameters within first lactation, however, require furthe r confirmation and investigation.