DOI: 10.1051/gse:2001124

Genet. Sel. Evol. 33 (2001) 397-415

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

Francis Barillet^a, Rachel Rupp^b, Sandrine Mignon-Grasteau^{a, c}, Jean-Michel Astruc^d and Michèle Jacquin<sup>a

a</sup>  Station d'amélioration des animaux, Institut national de la recherche agronomique, BP 27, 31326 Castanet-Tolosan Cedex, France
^b  Station de génétique quantitative et appliquée, Institut national de la recherche agronomique, 78352 Jouy-en-Josas Cedex, France
^c  Present address: Station de recherches avicoles, Institut national de la recherche agronomique, 37380 Nouzilly, France
^d  Institut de l'élevage, BP 18, 31321 Castanet-Tolosan Cedex, France

(Received 14 September 2000; accepted 13 February 2001)

Abstract
Genetic analysis for mastitis resistance was studied from two data sets. Firstly, risk factors for different mastitis traits, i.e. culling due to clinical or chronic mastitis and subclinical mastitis predicted from somatic cell count (SCC), were explored using data from 957 first lactation Lacaune ewes of an experimental INRA flock composed of two divergent lines for milk yield. Secondly, genetic parameters for SCC were estimated from 5 272 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. Predicted subclinical mastitis was unfavourably associated with the milk yield level. Such an antagonism was not detected for clinical mastitis, which could result, to some extent, from its low frequency or from the limited amount of data. In practice, however, selection for mastitis resistance could be limited in a first approach to selection against subclinical mastitis using 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. The genetic correlation between lactation SCC and milk yield was slightly positive (0.15) but showed a strong evolution during lactation, i.e. from favourable (-0.48) to antagonistic (0.27). On a lactation basis, our results suggest that selection for mastitis resistance based on SCC is feasible. Patterns for genetic parameters within first lactation, however, require further confirmation and investigation.

Key words: dairy sheep / somatic cell count / mastitis / genetic parameters / risk factors

Correspondence and reprints: Francis Barillet
    e-mail: Barillet@toulouse.inra.fr

© INRA, EDP Sciences 2001