Estimation of genetic parameters for litter size in Charollais, Romney, Merinolandschaf, Romanov, Suffolk, Å umava and Texel breeds of sheep

The objective of this investigation was to estimate genetic parameters for litter size in Charollais, Romney, Merinolandschaf, Romanov, Suffolk, Šumava and Texel breeds of sheep. These breeds account for more than three quarters of the recorded sheep population in the Czech Republic. A total of 143,896 lambing records from 1990 to 2012 were analyzed. Variance components and genetic parameters for litter size were estimated separately for each breed using the animal model with repeatability. The model equation contained ewe age as a fixed effect and random effects of contemporary group, permanent environment and direct additive genetic effect of the animal. Estimates of phenotype variance (σP2) increased across breeds (0.236 for Šumava to 0.779 for Romanov) with increasing breed average for number of lambs per litter. Variance component estimates for permanent environmental effect of the ewe were low (0.0001-0.0262). The variance of common environment of contemporary group (σCG2=0.0223-0.1309) had bigger influence on the total variability of litter size in almost all breeds then additive genetic variance (σa2=0.0146-0.0587). The lowest heritability and repeatability estimates were for the Šumava (h2 = 0.0619; rrep2=0.0823) and Romney breeds (h2 = 0.0626; rrep2=0.0811); while the highest were for Merinolandschaf (h2 = 0.1091; rrep2=0.1129). We conclude that genetic parameters did differ among the investigated breeds, which should be taken into account in breeding value estimation.