A SIMULATION-MODEL INCLUDING OVULATION RATE, POTENTIAL EMBRYONIC VIABILITY, AND UTERINE CAPACITY TO EXPLAIN LITTER SIZE IN MICE .1. MODEL DEVELOPMENT AND IMPLEMENTATION

Litter size in mice was studied using a model including ovulation rate , potential embryonic viability, and uterine capacity. Simulated resul ts were compared with experimental results from a selection experiment with mice. The four criteria of selection were selection on number bo rn (LS), selection on an index of ovulation rate and ova success (IX), selection on number born to unilaterally ovariectomized females (UT), and unselected control (LC). Comparisons were made to statistics of t he base generation and to responses after 13 generations of selection. Phenotypic and genetic statistics for uterine capacity were generated so that simulations produced the experimental means, standard deviati ons, and correlations between left and right litter size, as well as r esponses in number born using the LS, IX, and UT criteria. Statistics for the simulated data generally agreed with observed values. Simulate d heritability in the base generation for uterine capacity was .065. E xperimental and simulated responses per generation in litter-size thro ugh 13 generations of selection were .15 and .16, .17 and .18, and .10 and .11 for LS, IX, and UT, respectively. Simulated responses in uter ine capacity after 13 generations were 2.19, 1.60, and 3.40 for LS, IX , and UT, respectively. Simulated means for the base generation were 1 3.22 and 16.30 for ovulation rate and uterine capacity, respectively. Uterine capacity was an important component of the variability in litt er size; however, ovulation rate was the more Limiting component.