Divergent selection for uterine capacity in rabbits. I. Genetic parameters and response to selection.

A 10-generation divergent selection experiment for uterine capacity (UC) measured as litter size in unilaterally ovariectomized females was carried out in rabbits. A total of 2,996 observations on uterine capacity of does (up to four parities) was recorded. Laparoscopy was performed at d 12 of their second gestation, and ovulation rate (OR) and number of implanted embryos (IE) were recorded in 735 does. Prenatal survival (PS) was assessed as UC/OR, embryo survival (ES) as IE/OR, and fetal survival (FS) as UC/IE. Genetic parameters and genetic trends were inferred using Bayesian methods. Marginal posterior distributions of all unknowns were estimated by Gibbs sampling. Heritabilities of UC, OR, IE, ES, FS, and PS were 0.11, 0.32, 0.22, 0.04, 0.14, and 0.09, respectively. Genetic and phenotypic correlations between FS and ES were low, suggesting different biological mechanisms for the two periods of survival. After 10 generations of selection, the divergence was approximately 1.5 rabbits, or approximately 1% per generation. Approximately one-half of this response was obtained in the first two generations of selection, which may suggest the presence of a major gene segregating in the base population.