Abstract
A total of 13,066 first-lactation test-day records of 2,277 Valle del Belice ewes from 17 flocks were used to estimate genetic parameters for somatic cell scores (SCS) and milk production traits, using a repeatability test-day animal model. Heritability estimates were low and ranged from 0.09 to 0.14 for milk, fat, and protein yields, and contents. For SCS, the heritability of 0.14 was relatively high. The repeatabilities were moderate and ranged from 0.29 to 0.47 for milk production traits. The repeatability for SCS was 0.36. Flock-test-day explained a large proportion of the variation for milk production traits, but it did not have a big effect on SCS. The genetic correlations of fat and protein yields with fat and protein percentages were positive and high, indicating a strong association between these traits. The genetic correlations of milk production traits with SCS were positive and ranged from 0.16 to 0.31. The results showed that SCS is a heritable trait in Valle del Belice sheep and that single-trait selection for increased milk production will also increase SCS.
Highlights
Mastitis is one of the major diseases in dairy cows and ewes and has motivated extensive research toward improved udder sanitation and mastitis control (ElSaied et al, 1998)
Flock-test-day explained a large proportion of the variation for milk production traits, but it did not have a big effect on SCS
Information on the genetic relationship between SCS and milk yield and composition is lacking, and no references are reported in literature on dairy sheep reared in the south of Mediterranean area, where the husbandry system and the management are very different from those adopted for the breeds reared (i.e., Lacaune and Churra) in the north of the Mediterranean area
Summary
Mastitis is one of the major diseases in dairy cows and ewes and has motivated extensive research toward improved udder sanitation and mastitis control (ElSaied et al, 1998). Genetic studies of SCS in dairy sheep are more recent and less frequent than in dairy cattle. The few available genetic studies are on a limited number of breeds; for example, on the Churra (Baro et al, 1994; El-Saied et al, 1998) and Lacaune (Barillet et al, 2001; Rupp et al, 2001, 2003) breeds and the estimates are usually based on average SCS during the lactation. Information on the genetic relationship between SCS and milk yield and composition is lacking, and no references are reported in literature on dairy sheep reared in the south of Mediterranean area, where the husbandry system and the management are very different from those adopted for the breeds reared (i.e., Lacaune and Churra) in the north of the Mediterranean area
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