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ALTERNATIVE METHODS OF SELECTION FOR LITTER SIZE IN MICE (OVULATION RATE, UTERINE POTENTIAL)
Abstract
Direct selection for increased litter size may put less than optimum emphasis on the components of number born: ovulation rate and the proportion of ova shed that result in viable offspring. A study was initiated with mice to evaluate alternative methods of selection for increasing litter size. Selection on an index of litter size components (IX) and selection on litter size in unilaterally ovariectomized (right side) females (UT) were compared to ordinary selection for litter size (LS) and an unselected control (LC). Surgical alteration in the UT line was to produce a physiological model emphasizing expression of uterine potential independent of ovulation rate. Selection criteria were replicated to allow empirical estimation of the sampling variance associated with response. Based on estimates from the base population, total ovulation rate (TOR) was approximately twice as heritable as the proportion of ova shed resulting in viable offspring (TOS) (.33 vs .15). Estimates of the phenotypic and genetic correlations between TOR and TOS were near zero. The index of litter size components (I = 1.21(TOR) + 9.02(TOS)) was expected to improve accuracy of selection by 23% over direct selection for litter size. Evaluation of selection criteria after five generations revealed differences in number of fetuses at term for LS and IX versus LC of about one-half pup. No advantage of IX versus LS selection was apparent at this point in the study. Ova loss on the left side of the uterus tended to be less in UT females, corresponding with the ovariectomy procedures designed to challenge the left uterine horn. Realized heritabilities were .09 (+OR-) .07, .08 (+OR-) .11 and .35 (+OR-) .06 for LS, UT and IX, respectively. Response in IX index values was a result of an increase in mean TOR and a slight decrease in mean TOS. Consequently, response in litter size of the IX line was similar to that in LS. Using generation five evaluation results, mean index value for IX as a deviation from LC, divided by the cumulative selection differential at that point, was .10. Variation among replicates in response to selection was observed under each of the criteria evaluated.
Subject Area
Livestock
Recommended Citation
CLUTTER, ARCHIE CHRISTIAN, "ALTERNATIVE METHODS OF SELECTION FOR LITTER SIZE IN MICE (OVULATION RATE, UTERINE POTENTIAL)" (1986). ETD collection for University of Nebraska-Lincoln. AAI8706225.
https://digitalcommons.unl.edu/dissertations/AAI8706225