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

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.dairy sheep / somatic cell count / mastitis / genetic parameters / risk factors

Genetic parameters of somatic cell count in dairy sheep considering the type of mammary pathogen effect

“…Using test-day records throughout lactation in the Lacaune breed, Lagriffoul et al (1993Lagriffoul et al ( , 1996 found very similar repeatability estimates to ours, whilst our repeatability and permanent environmental variance values were somewhat higher than those obtained by El-Saied et al (1998) in the Churra breed. Similarly, in the model that excluded the mammary pathogen, the heritability values for the two half-udders (0.10 and 0.11) were similar to those more frequently obtained in sheep (El-Saied et al 1998;Barillet et al 2001) and (Emanuelson et al 1988;Da et al 1992;Schutz et al 1994;Roman and Wilcox 2000;and Kennedy et al 1982).…”

Mastitis in sheep – The last 10 years and the future of research

“…Higher resistance against mastitis of an indigenous Greek sheep breed, as compared to an improved high-production breed, was attributed to more efficient local defense mechanisms in the teat of ewes of the indigenous breed (Fragkou et al, 2007b). A genetic background to increased susceptibility in mastitis in dairy ewes has also been reported (Barillet et al, 2001;Rupp et al, 2009;Bramis et al, 2014). These authors have suggested that, in selection of ewes for resistance to mastitis, use of reduced log-transformed somatic cell score may be employed as an indirect trait.…”

Genetics of adaptation in domestic farm animals: A review

“…Subclinical mastitis is generally diagnosed by an increase in somatic cell counts (SCC) in the milk of cows and ewes, although in goats the predictive value of SCC is less established (Bergonier et al, 2003). SCC may also be used to help select for increased resistance to mastitis though recent estimates of heritability for SCC are generally low ranging from 0.10 to 0.20 (Mrode and Swanson, 1996;El-Saied et al, 1999;Barillet et al, 2001;Rupp et al, 2003;Serrano et al, 2003;Gonzalo et al, 2003;Legarra and Ugarte, 2005;Bishop and Morris, 2007). The review by Mrode and Swanson (1996) summarized many genetic estimates, concluding that the heritability of mastitis incidence in dairy cattle is low (∼ 0.04), as also is the heritability of SCC (0.11 ± 0.04), but the genetic correlation between the two is high at ∼0.70.…”