Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 1996
Publication Date: N/A
Interpretive Summary: Litter size at birth is a very important trait in domestic animals and mice are useful to help understand how litter size is determined. A model of litter size in swine was adapted for mice and simulated and experimental values were compared. The general agreement of values support the concept that ovulation rate, potential embryonic viability, and uterine capacity combine with each other to determine litter size. This information is important because alternative approaches to increase litter size can be studied.
Technical Abstract: Litter size in mice was studied using a model including ovulation rate, potential embryonic viability, and uterine capacity. Simulated results were compared to experimental results from a selection experiment with mice. The four criteria of selection were: LS=selection on number born; IX=selection on an index of ovulation rate and ova success; UT=selection on nnumber born to unilaterally ovariectomized females; and LC=unselected control. Comparisons were made to statistics of the 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 deviations, and correlations between left and right litter size, as well as responses in number born using the LS, IX and UT criteria. Statistics for the simulated data generally agreed with observed values. The simulated heritability in the base generation for uterine capacity was .065. Experimental and simulated responses per generation in litter size through 13 generations of selection were: .15 and .16, .17 and .18, and .10 and .11, respectively, for LS, IX and UT. Simulated responses in uterine capacity after 13 generations were 2.19, 1.60, and 3.40, respectively, for LS, IX, and UT. Simulated means for the base generation were 13.22 and 16.30 for ovulation rate and uterine capacity, respectively. Uterine capacity was an important component of the variability in litter size; however ovulation rate was the more limiting component.