Estimation of genetic parameters for test day milk production, somatic cell score and litter size at birth in East Friesian ewes

Abstract

Test day records of milk performance and litter size at birth were used to estimate genetic parameters for East Friesian milk sheep using a multivariate animal model. The analysis was based on 1746 lactation records including 9729 test day records of 1108 milk sheep distributed over 103 flocks. The milk records were sampled from 1992 to 2000. Flocks were located in Lower Saxony, Westphalia and Bavaria. The pedigree file contained 4267 animals. Using a multivariate test day model with fixed regression on the test day, the estimated heritabilities for milk, fat and protein yield were h 2=0.15 in all cases. For the fat and protein content and the somatic cell score (SCS) the heritabilities were h 2=0.09, 0.20 and 0.16, respectively. The heritability estimate for litter size at birth was h 2=0.04. The additive genetic correlations between milk yield traits in East Friesian milk sheep were very high and positive ( r g>0.68). On the other hand, the additive genetic correlations between yield traits and fat content and between yield traits and protein content were close to zero or even slightly negative. The additive genetic correlations between the SCS and the other milk performance traits were in the range of r g=−0.17–0.14. Litter size at birth was genetically positively correlated with all milk performance traits ( r g=0.01–0.08) and slightly negatively with SCS ( r g=−0.15). The genetic parameters estimated from field test records allow to achieve genetic progress in milk performance traits of East Friesian milk sheep.