Placental and fetal development in straightbred and reciprocal crosses of Yorkshire and Ossabaw swine.

Placental and fetal development were compared in 7 Yorkshire (Y) and 12 feral, Ossabaw (F) gilts mated to Y and F boars to produce straightbred and reciprocal cross litters (YY, YF, FY and FF, sire listed first). Gilts were slaughtered at d 75 +/- 2 of gestation. Ovulatory rate and litter size were higher in Y than in F gilts; however, rates of embyonal survival were similar in all groups. Groups differed in fetal body weight, metabolic body weight, crown-to-rump length, placental weight, metabolic placental weight and placental surface area, respectively. The YY group had highest values and the FF group smallest values for all variables except placental surface area. Pearson product-moment correlation coefficients of placental development with fetal length and weight across breeding groups were significant (e.g., placental surface area: fetal length, r = .67; placental surface area: fetal metabolic body weight, r = .76). It is concluded that the relationship between placental and fetal development observed in domestic swine is present in feral swine and crosses between domestic and feral swine at this gestational stage. These developmental measures are significantly influenced by fetal genotype and uterine environment but also by the breed of sire.