Inbreeding depression on growth and prolificacy tra its

This research aims at estimating inbreeding depress ion for growth and prolificacy traits in a rabbit population selected for growth rate for 60 generati ons. Data corresponded to 173,485 individuals of th e Caldes line founded in 1983. The effects of old, in termediate and new inbreeding (Fold, Fint, Fnew), a s well as classical (i.e. total cumulated) inbreeding (F) and 3 measures of ancestral inbreeding (AHC, F a.K and Fa.B) were estimated for average daily gain (AD G), slaughter weight (SW), number of kits born aliv e (NA), total number of kits (NT) and number of weane d kits (NW). For growth traits the effect of inbreeding was estimated with a model that included the fixed effects of year of birth, parity order a nd litter size as well as the corresponding inbreeding coefficient as a covariate (or alternatively the a ddition of Fold, Fint, Fnew covariates), plus the random ef fects of litter, batch and additive genetic effects . For the analysis of prolificacy traits, the model included the fixed effects of year of birth, physiological s tatus of the female at mating in addition to the covariate c orresponding to the inbreeding coefficient, as for growth traits, and the random effects of dam, batch and ad ditive genetic effects. There was a clear inbreedin g depression for all growth and prolificacy traits (10 g/d, -506 g, -7.4 kits, -6.2 kits and -6.2 kits for ADG, SW, NA, NT and NW, respectively on F). Ancestral in breeding coefficients Fa.K and Fa.B had also a negative effect on all traits, and results were not significantly different to those obtained with F. However, the effect of Fold and Fint was null whereas it was negative for Fnew, on growth traits but not on prolificacy traits. Similar results to those obtain ed for Fint and Fold were also observed using AHC, suggesting the possibility of purging by selection of deleterious recessive alleles affecting growth.