Breed differences in uterine and ovarian measurements in gestating swine

Ovulation rate, ovary weight, corpora lutea weight and uterine length were measured at 10 or 35 d of gestation in Duroc (199) and Yorkshire gilts (114). Embryos were counted at d 35. Yorkshires had significantly more corpora lutea than Durocs (13.6 vs 12.3 at d 10; 13.9 vs 12.4 at d 35). At d 10 breeds did not differ in uterine length, but by d 35 Duroc uteri were longer (P less than .01) than Yorkshire uteri (411 vs 375 cm) despite having fewer (P greater than .05) embryos (9.9 vs 10.5). Ovary weight did not differ between breeds at 10 or 35 d. Homogeneity analyses showed that the correlation matrices were significantly different between breeds at d 35 but not at d 10. In Durocs, high positive correlations existed between total embryo number and corpora lutea number (.57), ovary weight (.53) and corpora lutea weight (.25), whereas corresponding correlations were small in Yorkshires (.21, -.02 and -.03, respectively). In Yorkshires, strong negative correlations existed between total embryo survival and corpora lutea number (-.55), ovary weight (-.30) and corpora lutea weight (-.55), but in Durocs corresponding correlations were small (-.12, .14 and -.10, respectively). These results suggest that animal scientists should consider breed differences in levels of performance and its relationships among traits when designing or interpreting experiments.