Genetic parameters of litter weight traits of apri rabbits in Egypt

الملخص EN

Litter weight traits, (LW at birth; 21 and at weaning at 35 days post kindling), for two consecutive years on APRI rabbits (a synthetic line derived from the maternal Spanish V-line and the Egyptian Baladi Red breed), were genetically evaluated.

The data of litter weights (at birth, LWB; at 21 days, LW21 and at weaning, LWW) contained a total of 192 litters produced from 80 does pedigreed by 9 sires and 12 dams, were analyzed using Multi Trait Derivative Free Restricted Maximum Likelihood Animal Model (DFREML).

The Mathematical model of the analysis comprised the effects of year-season combinations (YRS) and parity (P) as fixed, as well as animal and uncorrelated permanent environmental effect as random effect. Heritabilities of the considered doe traits were relatively low being 0.17, 0.04 and 0.11 for litter weights at birth; 21 days and weaning; resp.

Furthermore, estimates of uncorrelated permanent environmental effects were rather low being 0.2, 0.002 and 0.008 for litter weight at the same manner.

From the previous heritability estimates, it can be concluded that family or within family selection could be more effective and valuable than individual selection to improve these traits of APRI does' rabbits under the Egyptian North-Delta climatic conditions. The ranges of the APRI does' transmitting ability (TA ± SE) for LWB, LW21 and LWW were (0.152 ± 0.020, 0.340 ± 0.050 and 1.167 ± 0.180 Kg.) with the accuracies being 0.350, 0.340 and 0.184.As for APRI dams' transmitting ability (TA ± SE), the ranges for LWB, LW21 and LWW were 0.09 ± 0.03, 0.2 ± 0.07 and 0.7 ± 0.03 Kg.

with the accuracies being 0.84, 0.83and 0.84; resp. Similarly, the ranges of APRI sires' transmitting ability (TA ± SE) for LWB, LW21 and LWW were 0.11±0.02, 0.24 ±0.06 and 0.81±0.19Kg with the accuracies being 0.51 % for all litter weight traits.

Interestingly, and though of the larger numbers involved, ranges of accuracies estimates (rAP) of the predicted breeding value (BV) of APRI rabbits were mostly higher in the dams data set followed by those of does. The estimates of correlation, however, were age dependent and decreased as age advance, indicating correlated response to selection that should be considered in selection plans.

Selection for LW may not be practically and realistically associated with a correlated improvement in the later-ages does' performance which in turn may have its impact on generation intervals and relatively amplify and enlarge selection costs. In addition, estimated epigenetic trends (EP), for litter weight traits under study suggested that it is possible to achieve slow, but simultaneous improvement of litter traits with selection program in rabbits.

LW traits recorded generally a negative EP trend during the majority of the year-seasons under study.

However as regard to EP with parities, the high LW response was postponed to the later parities.