Data on 841 purebred Bauscat, White Flander, Giza White and Baladi Red litters provided estimates of genetic, phenotypic and environmental parameters for gestation length, litter size at birth and at weaning, mortality and sex ratio at weaning. A total of 170 daughters (paternal half-sisters) of 76 sires were available for the analysis. No important differences were detected among breeds for litter traits studied except litter size at weaning (P < 0·001). Year of kindling affected (P < 0·001) gestation length, litter size at birth and mortality percentage. No clear patterns of the effect of parity and month of kindling on litter traits were observed. The sire of the doe and doe within sire affected most of the traits studied. Estimates of heritability indicated that the sire's genetic contribution to litter traits are much higher during the pre-natal period than for the suckling period. Estimates of repeatability for litter traits studied were relatively low. Genetic and phenotypic correlations between gestation length and other litter traits were relatively low. Litter size traits were positively correlated both genetically and phenotypically. Estimates of genetic and phenotypic correlation between litter size traits and preweaning mortality were generally negative. Phenotypic and environmental correlations were generally very similar in size and sign. Predicted direct selection was shown to give greater improvement in litter size at birth than indirect selection through litter size at weaning. |
