Relationships between uterine length and number of fetuses and prenatal mortality in pigs.

Relationships between the length of uterine horn and number of fetuses and prenatal mortality were characterized in 320 pregnant pigs at 3, 5, 7, 9, 11, 13 and 15 wk of gestation in a cross-sectional design. Genital tracts of all pregnant animals available on the days of collection were measured. Length of each uterine horn, numbers of fetuses and corpora lutea (CL) were recorded and prenatal mortality was calculated. With each additional fetus, length of the uterus increased 10 cm regardless of stage of gestation (P less than .001). The association of number of fetuses and uterine length was local and confined to that horn in which the fetus resided and did not extend to the opposite horn. As number of CL increased, number of fetuses also increased as did prenatal mortality. There was a significantly negative correlation between uterine length and prenatal mortality when animals were classified into four groups on the basis of number of CL; less than 10, 10 to 14, 15 to 18 and greater than 18. Results indicated that the number of fetuses and prenatal mortality were closely correlated with length of the uterus. Length of the uterus appeared to be an important limiting factor to litter size as number of CL increased.