Genetic and maternal variance components of stillbirths and pre-weaning mortality in purebred rabbits

Records (2731) from commercial breeds of rabbits (Bauscat, New Zealand White and Californian) were analyzed to investigate the effects of breed, sire, doe, season of delivery, parity and litter size al birth on stillbirths and pre-weaning mortality at different ages, in addition to, gestation length or litter weight at birth as independent covariates were also estimated. Total losses prior to weaning in all breeds were approximately 21\%, largely due to stillbirths (Sb\%) and subsequent mortality to 29 days (M 20\%) then followed by 21 to 30 days (M21-M30\%). Differences between breeds were nonsignificant in all mortality traits studied. Season of delivery, parity of doe and liner size at birth significantly affected mortality traits studied. The partial linear regression coefficients of Sb, M20 and M30 on gestation period were significant. The linear and quadratic regression coefficients of all mortality traits on liner weight at birth were significant. The antagonistic quadratic regression of M20 and M30 on tilter weight at birth was observed. The additive genetic variance (V-A) and maternal effect (V-EC) for mortality rate traits were low and close to 0. The residual environment variance V-EW was high for stillbirths and all preweaning litter mortalily. The repeatability (t) values for Sb and preweaning mortality rate traits were low. High VEW for all mortality traits indicated that genetic improvement by selection would be difficult, while improvement in the environmental and managemental factors might improve the performance of the young. At the same time, evaluating doe for natal and postnatal litter mortality, adjustments might be made by other performance traits such as litter size and litter weight at birth or gestation period.