Comparison of Ordinary and Restricted Selection Indices on Genetic Gain of Body Weight in Iranian Moghani Sheep

The effect of ordinary and restricted selection indices on body weight at different ages changes in birth weight of Iranian Moghani sheep was studied. Traits in the aggregate genotype were birth weight (BW), body weights at 3 (BW3) and 12 months of age (BW12). Two ordinary selection indices (I1 and I2) and two restricted selection indices (R1 and R2) were constructed. BW and BW3 were included in I1 and R1 and BW, BW3 and BW6 were included in I2 and R2. The ranges of expected genetic gains in I1 and I2 for BW, BW3 and BW12 per generation were 0.080 to 0.068, 0.210 to 0.177 and 0.546 to 0.662 kg, respectively. Increasing BW may cause a disorder in the future of breeding goal due to dystocia. Restricted selection indices were constructed to increase BW3 and BW12 while keeping genetic gain in BW to zero. Under selection by indices of R1 and R2 the amount of genetic gain in BW was zero, while considerable genetic gains were obtained for BW3 (0.094 to 0.062) and BW12 (0.39 to 0.60). Ordinary and restricted selection indices were then evaluated in a simulated population. Predicted genetic gains for BW, BW3 and BW12 from ordinary and restricted selection indices were similar to the predicted genetic gains. For both restricted selection indices (R1 and R2) predicted genetic gains for BW3 and BW12 in the simulated population increased over the generations whereas BW decreased slightly over the generations.