Biology of Reproduction, Vol 23, 929-934, Copyright © 1980 by Society for the Study of Reproduction

Reproduction in Domestic and Feral Swine. II. Interrelationships Between Fetal Size and Spacing and Litter Size

¹ Department of Dairy and Animal Science, The Pennsylvania State University, University Park, Pennsylvania 16802

Fetal and uterine relationships were evaluated and compared in 17 feral-Ossabaw and 12 Yorkshire primiparous gilts slaughtered at 80, 90, 100, or 110 days of gestation. Feral fetuses were smaller than Yorkshire fetuses at all gestational ages examined (P<0.01). Within lines, fetuses located at the cervical, middle, or oviductal thirds of the uterus were similar in weight (P>0.1). The mean length of uterine horn per fetus increased linearly from Day 80 to Day 110 of gestation in the Yorkshire (r = 0.95, P<0.01) and feral (r = 0.90, P<0.01) lines. Uterine horns containing more fetuses were generally longer than horns with fewer fetuses. Total weight of fetuses in the uterine horn was related to the number of fetuses in the horn in both the ferals (r = 0.76, P<0.01) and the Yorkshires (r = 0.57, P<0.01), but individual fetal weights decreased as the number of fetuses in the litter increased. In either line there was no consistent relationship between fetal weight and amount of uterine space available to each fetus, as indicated by distance between adjacent fetuses. These results indicate that the small litter size observed in the feral line is not attributable to a limitation of uterine capacity during late gestation. Further, the uterus of the feral pig may have the capability for greater growth in length during pregnancy than does the uterus of the Yorkshire pig.

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ACKNOWLEDGMENTS The authors thank V. E. Hazlett for caring for the animals, J. L. Watkins for assistance with slaughter of the animals, and Mrs. Marlene Sovyak for typing the manuscript.