Selection indexes for genetic improvement of yearling weight in Egyptian buffaloes

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 (r(TI)=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 I(s) 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).