Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2012
Publication Date: July 1, 2012
Citation: Vallet, J.L. 2012. Limitations in uterine and conceptus physiology that lead to fetal losses [abstract]. Journal of Animal Science. 90 (Supplement 3):6 (Abstract #15).
Conceptus losses in livestock occur throughout gestation. It is clear that the uterus and embryo/placenta/fetus play interconnected roles in these losses, the details of which depend on the period of gestation and the species. Studies in sheep and pigs have indicated that the uterine glands are essential for full fertility, based on experiments where gland development was reduced through the use of exogenous hormones. In sheep and cattle, normally the uterus is well able to support more than a single fetus, although these species differ in the consequences of multiple births. When two conceptuses are present, the placentas of cattle often anastomose, putting one fetus at risk if the other is lost. One likely reason this does not occur in sheep is because sheep embryos undergo intrauterine migration, similar to pigs. In pigs, the equidistant separation of conceptuses is likely to be essential for optimizing conceptus survival, as is the simultaneous and uniform elongation of blastocysts that occurs during the time of maternal recognition of pregnancy. Other studies in pigs have indicated that the size of the uterus influences litter size and therefore fetal losses. In response to crowded intrauterine conditions in the pig, increased conceptus losses begin to occur between day 30 and 40 of pregnancy, and further losses occur sporadically during later gestation. There is evidence that improved fetal erythropoiesis can reduce these losses. Other studies indicated that profound changes in placental development occurred under crowded intrauterine conditions that may contribute to losses during late gestation. Reductions in placental stroma formation may compromise the ability of the pig placenta to adapt to reduced uterine space. Consistent with this, both hyaluronan and hyaluronidase activity are decreased in the placentas of small compared to large fetuses. These results suggest that improvements in placental stroma formation could improve placental ability to compensate for reduced intrauterine space, resulting in increased placental function and reduced fetal losses during late gestation.