Selection for Litter Size by Using the Ratio of Piglet Weight: Placental Weight as a Measure of Placental Efficiency

The Chinese have been selectively breeding pigs for 7,000 to 10,000 years for increased numbers of pigs born, regardless of birth weight, indirectly resulting in the optimization of placental size and vascularity. In the United States, pig producers have generally selected for larger piglets at birth, resulting in a marked variation in placental size and vascularity. This tremendous variation in placental size and vascularity present within a litter may be ultimately limiting litter size. Therefore, by selecting against the large relatively avascular placentae, the potential for dramatically increasing litter size exists

Selection for Litter Size by Using the Ratio of Piglet Weight: Placental Weight as a Measure of Placental Efficiency

The Chinese have been selectively breeding pigs for 7,000 to 10,000 years for increased numbers of pigs born, regardless of birth weight, indirectly resulting in the optimization of placental size and vascularity. In the United States, pig producers have generally selected for larger piglets at birth, resulting in a marked variation in placental size and vascularity. This tremendous variation in placental size and vascularity present within a litter may be ultimately limiting litter size. Therefore, by selecting against the large relatively avascular placentae, the potential for dramatically increasing litter size exists.</p

Effect of Uterine Environment and Fetal Genotype on Placental Size and Efficiency

Optimum conceptus (fetal and placental) growth appears to be achieved through the combination of both uterine and fetal-directed mechanisms. The uterus, in which a litter of conceptuses develops, has the major impact on limiting the size each conceptus ultimately attains; however, the genotype of each conceptus can differentially resist this effect, resulting in littermate conceptuses of different sizes. In contrast, the genotype of the conceptus modulates placental vascular density and thus placental efficiency. The ability to both limit placental size while at the same time increase placental vascular density of conceptuses of U.S. pig breeds would allow pork producers the potential of achieving an optimal litter size and increasing profitability.</p