A major limitation for increasing litter size in swine is embryonic loss that occurs during the 2nd to 3rd wk of gestation. High ovulation rates of modern sows have more than supplied the potential number of embryos necessary to improve litter size. The current challenge is determining how early conceptus development affects the ability to maintain the viability through the remaining 90 d of gestation to maximize farrowing house production. To achieve this, it is neces- sary to identify and understand the possible causes of embryonic death. Because fertilization rates are gener- ally high in swine, early embryonic loss during the first 20 d of gestation is considered to critically effect poten- tial litter size. There are three periods during which early embryonic loss can occur: 1) pre-elongation devel- opment, 2) trophoblastic elongation, and 3) placental attachment. The first two periods are related to time of fertilization and subsequent developmental rate for each individual embryo within the litter. Asynchrony in embryonic development relative to uterine develop-

http://thebiohaven.yolasite.com/resources/J%20ANIM%20SCI-2002-Geisert-E54-65.pdf

Early embryonic survival in the pig: Can it be improved?

Unus pro omnibus, omnes pro uno: A novel, evidence-based, unifying theory for the pathogenesis of endometriosis.

Maternal recognition of pregnancy reflects the various ways in which the mother responds to the presence of a conceptus within her reproductive tract. A part of the biochemical information she senses may be irrelevant to pregnancy outcome, but some reflects the attempts by the conceptus to gain some measure of control over corpus luteum function, uterine blood supply, the mother's immune system, and other aspects of maternal physiology. Most probably as a result of ongoing genetic conflict between the mother and the conceptus, a bewildering range of placental structures and trophoblast signaling mechanisms are encountered in eutherian mammals despite the fact that the uterus and conceptus share a common interest, which is the successful outcome of the pregnancy. Here we review some of the ways that such mammals maintain luteal function in early pregnancy and briefly discuss the related topics of embryonic loss and maternal monitoring of conceptus fitness. We next address the view that the conceptus is an intruder, recognized as foreign by the mother, that likely survives by using strategies analogous to those employed by successful parasites. In this context, we describe the pregnancy-associated glycoproteins, multiple isoforms of which are released at the trophoblast-endometrial interface during pregnancy of ungulate species. These molecules, which are structurally related to pepsin, are proposed to bind and sequester antigenic peptides, thereby serving an immunoprotective role.

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Maternal recognition of pregnancy.

Establishment of pluripotent cell lines from porcine preimplantation embryos.

The objectives of this study were to develop a rapid method for sex determination for several mammalian species using polymerase chain reaction (PCR) and to use this method to determine whether there is a significant developmental difference in spherical diameter between male and female d-10 or -11 porcine embryos. The PCR system was developed and verified using genomic DNA from pigs of known sex, then it was tested with genomic DNA from several other mammalian species. Sex is determined by amplification of two genes in a single reaction. The presence or absence of a region of the Sry (sex-determining region Y) gene determines sex, and amplification of the Zfy (male) or Zfx (female) genes acts as a positive control for PCR. Sex determination was successful for all animals tested, including pigs, cattle, sheep, goats, llamas, horses, humans, baboons, dogs, cats, rats, and mice. A total of 209 embryos were collected from 21 crossbred gilts on d 10 or 11 of gestation, and their diameters were measured. No significant difference in embryo diameter was detected between male and female embryos, indicating that sexual dimorphism in embryonic growth in pigs does not occur before the period of rapid embryo elongation. The present sexing technique using PCR is rapid (approximately 6 h from receipt of embryos to results), and it may be useful for examining the effects of sex on any trait of interest in early porcine embryos and embryos from several other mammals.

Sex identification in mammals with polymerase chain reaction and its use to examine sex effects on diameter of day-10 or -11 pig embryos.

Comparison of the timing of pig preimplantation development, alterations in the ultrastructure of embryonic germ layers, and cytological changes of the uterine epithelial cells leads to the supposition that a close relationship exists between embryonic and uterine development during early pregnancy. The results of in-vitro studies of embryonic development and of experiments concerning asynchrony between embryos and uterine environment confirm this supposition, especially as far as the post-hatching period is concerned. It is suggested that successive steps in embryonic germ layer differentiation may induce specific developmental events and secretory activity of the embryos. A mutual influence of maternal and embryonic tissues appears to exist, but we can only speculate about the causes of many of the described phenomena.

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der Lende T. Van

Papers

Embryonic and uterine development during early pregnancy in pigs