Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 1996
Publication Date: N/A
Interpretive Summary: Selection to increase litter size is a slow process and alternative approaches need to be studied. Several different methods to increase litter size of mice were evaluated by simulation. Results indicated that selection for combinations of components of litter size (ovulation rate with ova success or uterine capacity) would be more effective than practicing selection directly for litter size. Selection for each component by itself would produce smaller changes than direct selection for litter size. These results are important because methods to increase litter size more rapidly are identified.
Direct selection for litter size was compared to selection for ovulation rate, ova success, or uterine capacity and to selection for indexes of ovulation rate with ova success or uterine capacity. Selection was simulated for 10 generations in a mouse population. Simulation was based on a model integrating ovulation rate, potential embryonic viability, and uterine capacity. Two indexes including ovulation rate (OR) and ova success (OS) were I = .291 x OR + 2.19 x OS and I = .165 x OR + .736 x OS. Heritabilities for ovulation rate and ova success, assumed in the simulation and to derive the indexes, were .25 and .06, respectively. The first index was derived from actual data from the base population of a selection experiment, and the second index was derived assuming the model parameters. Both indexes resulted in the same response in litter size, 12.9% greater than response to direct selection for litter size. Two indexes including OR and uterine capacity (TUC=true total uterine capacity UC=uterine capacity measured as number born for a female with right ovary excised) were I = .881 x OR + .223 x TUC and I = .876 x OR + .568 x UC. Heritabilities assumed for uterine capacity were .09 (TUC) and .065 (UC). The first index assumed true parameters for uterine capacity (TUC) and resulted in a response in litter size that was 23.9% greater than that for direct selection for litter size. The second index was calculated using parameters estimated under a unilateral-ovariectomy model and resulted in a response that was 14.7% greater than direct selection for litter size. Selection for OR, TUC, UC, or OS resulted in responses that were 4.5, 48.5, 38.7 or 74.8%, respectively, less than that from direct selection for litter size.