Dam and litter inbreeding and environmental effects on litter performance in Botucatu rabbits
The purpose of this study was to evaluate the effects of the inbreeding of the dam (Fd) and of the litter (F1), parity of dam, and month and year of birth on number of young born alive (NBA) and weaned per litter (NW), total litter weaning weight (LWW), mean weaning weight (MI/VW) and litter pre-weaning mortality rate (LM) in Botucatu rabbits. Data on 1,065 litters were collected from 1992 to 1994 at the UNESP rabbitry located in Botucatu, SP, Brazil, and analysed by least-squares method. Litters were weaned at 30 days of age. Values of Fd and F1 ranged from zero to 0.3309 and averaged 0.0717 ± 0.0015 and 0.0979 ± 0.0018, respectively. The overall means and standard-errors of NBA, NW, LWW, MWW, and LM were 7.458 ± 0.076, 5.869 ± 0.067, 3576 ± 36 g, 626.6 ± 3.4 g, and 0.1954 ± 0.0063, respectively. Year and month of birth influenced MWW (P < 0.001) and tended to affect LWW (P < 0.07). Parity number affected (P < 0.001) NBA, NW and LWW. The first litter of a female presented (P < 0.05) lower NBA NW, and also LWW when individually compared to parities two to five. The inbreeding coefficient of the dam showed a negative linear association with NBA (P < 0.001), NW (P < 0.001), LWW (P = 0.007), and MWW (P < 0.001), but not with LM (P = 0.576), suggesting that the reduction in NW reflected a decrease in NBA but not an increase in LM. lt was predicted that for each increment of 10 % in F d, a corresponding reduction of 0.805 young born, 0.589 young weaned, and 211 g in LWW were observed, while MWW increased by. 29.1 g. The reduction in NW (10.0 % of the overall mean of the trait) was proportionally greater than the reduction in LWW (5.9 % of the overall mean of the trait), providing a partial explanation for the increase in MWW. No effect of F1 (P > 0.05) was detected for any litter performance traits.
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