Genetic and environmental sources of variation for milk yield traits in Barbaresca siciliana breed

Abstract

Multi-trait animal model procedures were used to calculate variance for milk yield traits in the Barbaresca siciliana breed. The recorded data consisted of 14 791 lactations from 6678 ewes distributed among 44 herds from six provinces in Italy. The data-set with pedigree information used for the estimation of genetic parameters and correlation, included 6678 ewes with records, 757 dams, 4 paternal grandams, 28 maternal grandam and 2 maternal great-grandams, all without records, and additionally 301 sires, 3 paternal grandsires, 11 maternal grandsires and 1 maternal great-grandsires. The variables considered in the present study were the milk yield at 100 days (MY-100), 120 days (MY-120), 180 days (MY-180), 200 days (MY-200); total milk yield (TMY), milk yield extended to 120 days (EMY-120) and milk yield extended to 180 days (EMY-180). The influence of flock (F), production year (Y), lambing season (L) and lactation number were significant for all milk production traits and lactation length. In the model with interaction, factors flock/year/season effect (FYS) and order of lambing by season effect (LBS) were significant with regard to lactation length. Variance component estimates for eight traits showed lower values for genetic variance, which is rather atypical when compared to published values in several studies for dairy sheep and goats. Estimates of heritability for all productive characteristics ranged from 0.14 to 0.15. The rank correlations between breeding values for the eight traits considered, confirmed the results of the genetic correlation analysis. The first 20 animals were ranked according to the breeding values estimated from MY-100, EMY-120, EMY-180. Three animals ranked according to EMY-120 and EMY-180 lost more than five positions and only two animals gained more than five positions. Variation in the classification of animals with breeding values that were also estimated with TMY, was very high. The correlated response for TMY is higher when selecting the animals according to EMY-180 (92%) rather than according to EMY-120 (78%) or MY-100 (76%).