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Effectiveness of index and elite selection methods

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  • Mice were used to compare the index and elite selection methods for simultaneous selection of four traits. Selection was for litter size, birth weight, weaning weight and post-weaning gain. Progress was evaluated by examining total phenotypic merit. The standard deviations from the cycle mean for the four traits were summed to give total merit. Mice were selected for both an increase and a decrease in each of the four traits under index and elite selection methods. Two lines were maintained for each direction and method of selection as well as two randomly selected control lines. Elite selection differs from index selection in that one-fourth of the parents are selected for each of the four traits, regardless of the performance in the other three traits. An attempt was made to mate twenty females and four males each generation. In general, progress within lines was small and irregular. A quadratic line was fitted through the means of lines selected alike to estimate the progress during approximately six generations of selection. Progress in the control, high index, high elite, low index and low elite lines for total merit was -0.51, +0.57, +0.47, -0.47 and +0.30 units respectively. Corresponding selection differentials were +1.97, +7. 16, +6. 36, -5.14 and -1.25 units for the same lines respectively. Estimates of heritability based on upward selection were 8. 0% and 7. 4% for high index and high elite selection respectively. Only the high elite selection method simultaneously changed all four individual traits in the desired direction. The elite method resulted in the selection of sires with greater phenotypic variance than did the index method. The selection of parents with greater phenotypic variance did not result in greater phenotypic variance in their progeny. It was found that parents selected for different traits in the elite system did not leave equal numbers of offspring. Thus, it was difficult to apply the proposed selection pressures for each trait. Since the present study is inconclusive, suggestions are made for further study of the elite selection method.
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