Abstract. Estimates of genetic and phenotypic parameters for body weight at birth, 3, 6, 9, and 12 months of age, and for preweaning and postweaning average daily gain were computed and used to construct 14 selection indexes to improve the 12-month weight in Egyptian buffaloes. The full index incorporating body weight at birth, 3, 6, 9 and 12 months of age had the highest correlation with aggregate breeding value (rTI=0.63). The correlation fell to 0.62 when body weight at birth and 3 months were omitted from the index. Selection for body weight at 12 months of age alone is expected to be 76.2 % as efficient as selection for the full index. The maximum expected genetic gain in 12-month body weight was 8.85 kg/generation when all five body weights were included in the index; this decreased to 8.09 kg/generation when body weights at birth, 3 and 6 months were excluded and further decreased to 6.94 kg/ generation when selection based on yearling weight only. From the practical standpoint, selection on I5 involving body weight at 9 month of age can be considered as the best for improving body weight at 12 month since its application is earlier, less expensive, higher accuracy than any index excluding body weight at 12 month and giving reasonable amount (+5.39 kg) improvement in yearling weight as compared to direct selection (+6.94 kg).
Abstract. Estimates of phenotypic and genetic parameters of body fat partition and other related traits were calculated using an experimental material of 152 New Zealand White rabbits of 15 bucks and 42 adult does. To construet nine selection indexes aiming at improving fat partition, estimates of phenotypic and genetic parameters for weight and linear dimensions of the live body were also obtained. The aggregate genotype included the percentage total body fat depositing subcutaneously and intermuscularly at the marketing age of 12 weeks. The füll index included the weaning body weight, marketing body weight, body length, loin width and heart girth. The full index had the highest correlation with the true breeding value (rT| = 0.597). Comparable accuracy (rTi = 0.561) would be expected from the best-reduced index (I7 = 0.009 BW –0.988 HG) combining marketing body weight and heart girth. At each round of selection with intensity =1, such a reduced index is expected to result in developing rabbits with advantageous fat partition in terms of higher percentage total body fat depositing subcutaneously (+0.35 unit %), intermuscularly (+1.91 unit %) and intramuscularly (as reflected by 0.15 unit % increase in carcass muscle yield. As compared with its unrestricted form, the best reduced index reduced to zero change in total body fat (I7(TBF)) would result in drastic decline in percentage total fat depositing as kidney knob and Channel fat (+0.32 vs. –0.18 unit %) with little amelioration in percentage total fat aecumulating in the other depots. Selection on I7(TBF) instead of 17 would reduce improvement in marketing body weight (+0.52 vs. +0.33 gm), carcass yield (+0.10 vs. 0.04 unit %) and carcass boneless meat yield (+0.19 vs. 0.07 unit %) with increase of gain in carcass muscle yield (+0.15 vs. 0.32 unit %).
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