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

Abstract

Summary Genetic parameters for somatic cell count (SCC) from half‐udder milk were estimated from 4692 monthly test‐day records from each half‐udder of 1337 Churra ewes belonging to seven dairy flocks. The total number of observations was 9348. Variance and co‐variance genetic components were estimated using a multitrait repeatability animal model. The log SCC of the right and left half‐udders were considered as two dependant variables in the model. The species of organisms causing intramammary infection were identified and included or not in the analysis as a fixed effect. The inclusion of the mammary pathogen fixed effect did not influence the estimation of heritability. However, the proportions of permanent environmental variance and repeatability were significantly reduced in comparison with the model that did not include this effect. On the other hand, the genetic correlation between SCC in milk from left and right glands was close to unity, and no differences were detected between both glands for all genetic estimates. The importance of the mammary pathogen factor was evaluated in comparison with the other fixed effects studied, which in relation were of little importance.

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.…”

Estimation of genetic and phenotypic parameters for bacteriological status of the udder, somatic cell score, and milk yield in dairy sheep using a threshold animal model

“…As a consequence, correlated traits have been suggested to increase the efficiency of selection for mastitis resistance. In particular, SCC has been promoted as an indirect method of predicting mammary infections (Boettcher, 2005) and as a selection criterion to improve mastitis resistance (Gonzalo et al, 2003). It has been indeed demonstrated that mastitis causes an increase in SCC in small ruminants (Leitner et al, 2004;Sanchez et al, 1999;Zeng et al, 1997) (e.g., Heringstad et al, 2006;Olde Riekerink et al, 2007).…”

Assessment of genetic variation for pathogen-specific mastitis resistance in Valle del Belice dairy sheep

“…In sheep a heritability estimate of 0.09 for infection status assessed by bacteriological analyses was reported by Riggio et al [ 24 ] and Tolone et al [ 25 ] in the Valle del Belice breed using a threshold animal model assuming a probit link function. Gonzalo et al [ 39 ] estimated genetic parameters of SCC in Churra sheep considering the type of mammary pathogen using a multitrait repeatability animal model. They reported that the effect related to the type of pathogen accounted for 32.5 % of the total variance in SCC, a value similar to that obtained for the residual effect (34.9 %), indicating a high relative importance of the type of pathogen in the decomposition of the variance for SCC.…”