Document Type : Original Article
Authors
Animal Production Department, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima, 11241 Cairo, Egypt
Abstract
This study aimed to investigate the consequences of selection for post-weaning growth performance on carcass and tissue weight distribution traits using selection indices in rabbits through the multi-trait animal model. The experimental material involved 218 New Zealand White (NZW) rabbits, the progeny of 24 bucks and 93 adult does. The aggregate genotype of weaning weight (WW), slaughter weight (SW), and average daily gain (DG) from weaning to slaughter were included. The same three traits were used with different combinations as a source of information.
The cut percentage of hind leg (HLW), fore leg (FLW), loin (LOW), and thoracic cage (TCW) were the carcass weight distribution traits. While carcass tissue weight distribution traits were represented as a percentage of meat and bone in each cut, respectively occurring in the hind leg (HLM and HLB), fore leg (FLM and FLB), loin (LOM and LOB), and thoracic cage cut (TCM, TCB). The full index (I1) including all sources of information: I1 =23.5WW –18.0SW +1212.8DG had the highest correlation with the aggregate genotype traits (rTI
=0.84). Dropping DG from the full index to construct I2 or SW to construct I3 or WW to construct I4 did not affect the accuracy of selection (rTI =0.83). The index included weaning weight alone (I5) was the most accurate single trait index (rTI =0.73). Among all reduced indices, which had the same accuracy, the index I2 was the best for being easy to measure.
Applying the best accurate indices (I1, I2, and I5) are expected to produce rabbits characterized by heavier body weight at weaning (88.80 to 108.10gm) and slaughtering (111.50 to 146.65 gm) with faster daily gain from weaning to slaughter (0.03 to 0.92 gm/day). This improvement would be coupled with changes in the distribution of carcass weight (decrease by -0.41 to -0.43% in HLW and by -0.05 to -0.01% in TCW and increase by 0.18 to 0.20% in FLW and by 0.11 to 0.14% in LOW), carcass meat weight distribution (decrease by -0.01 to -0.26% in HLM, -0.91 to -1.41% in FLM and increase by 0.13 to 0.64% in LOM and 0.45 to 0.58% in TCM) and in bone weight distribution (decrease by -0.07 to -0.08% in
FLB and by -0.12 in TCB% and increase by 0.11 to 0.15% in LOB with fluctuated change in HLB by -0.09 to 0.07%).
As compared with their unrestricted forms, the restricted indices I7(HLM) and I8(HLM) would entail an only a slight reduction in accuracy of selection (rTI= 0.76 and 0.72, respectively) with acceptable improvement in WW (+104.7 and 108.2gm, respectively) and SW (+119.8 and 108.1gm, respectively) with an unfavorable increase in HLB by 0.37 and 0.07%, respectively.
Conclusively, Use of weaning weight (WW) and slaughter weight (SW) as sources of information (I2) in the following index: I2= 3.8 WW + 1.5 SW (rTI = 0.83) would be recommended to
maximize the post-weaning growth traits regardless of the deterioration in carcass tissue weight distribution. However, the following restricted index:
I7(HLM) = -29.4 WW + 34.5 SW -2110.4 DG (rTI = 0.76)
would be a preferred choice to the breeder, taking into consideration the expected deterioration in carcass tissue weight distribution, for biological and rabbit meat consumer desires reasons.
Keywords
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