Variance components and response to selection for reproductive, litter and growth traits through a multi-purpose index
Variance components and genetic trends were estimated for number of services/parturition (NS), parturition interval (PI), number born alive (NB), number weaned/litter born (NW), litter weaning weight (LW), 30-d individual weaning (WW) and 70-d (W70) weights and a mullipltHrait selection index (MI) in rabbits from a closed population in Botucatu, Southeast Brazil. Phenolypic values for two litter (NW and LWW), and two individual performance (WW and W70) traits were included in the index. Individual selection according to the multiple-trait index was practised for a 2.6-yr period (January 1992 through July 1994). Performance records collected for five years (July 1989 through July 1994) on 2,162 parturitions, 2,122 litters, and 10,440 individuals were included in the analyses. The general model used to estimate variance components and breeding values included the random effects of animal, maternal genetic, and permanent dam effects (for reproductive and litter traits) or common litler effects (for individual weight traits), and fixed effects of parity, parturition date, sex (for individual weight traits) and covariates of the inbreeding coefficient of the dam (for reproductive and litter traits) or of the rabbit and its dam (for individual weight traits). Inbreeding coefficients ranged from 0 to 0.36. For reproductive and litter traits, estimates of permanent dam effects ranged from 0.03 to 0.09 and estimates of direct heritability ranged from 0.02 to 0.05. The estimated genetic correlation between NS and PI was 0.73. For WW, W70, and MI, estimates of direct and maternal heritabilities and direct-maternal genetic correlation were 0.08, 0.08 and 0.28; 0.18, 0.05 and 0.76; and -0.35, 0.59 and -0.46, respectively. Estimated common litter effects for WW and W70 were 0.44 and 0.26, respectively. Estimates of direct genetic trends/yr for NS, PI, NB, NW and LW were -0.0037 ± 0.0003 services, -0.200 ± 0.030 d, 0.034 ± 0.010 young/litter, 0.039 ± 0.006 young/litter, and 35.2 ± 4.6 g, respectively. Estimates of direct and maternal genetic trends/yr were 6.74 ± 0.39 g and 1.58 ± 0.60 g for WW; 17.20 ± 1.22 g and 8.35 ± 0.71 g for W70; and 4.91 ± 0.65 and -2.34 ± 0.39 for MI. Individual weight traits showed meaningful genetic trends with multiple-trait selection, whereas reproductive and litter traits showed slight, but favourable genetic changes. lt seems possible to achieve slow, but simultaneous improvement of litler and growth traits with a multipletrait selection program in rabbits.
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