Bioscientifica Proceedings

Summary. In the pig, establishment of pregnancy begins about 11-12 days after the start of oestrus. The ability of pig conceptuses to synthesize and release oestrogens during this period, as well as the ability of exogenous oestrogens to induce pseudopregnancy when administered from Day 11-15 of the oestrous cycle, provide evidence for an involvement of oestrogen in the maternal recognition of pregnancy in the sow. Oestrogen derived from the conceptus or ...

The hypothalamic GnRH pulse generator that regulates intermittent GnRH discharge into the pituitary portal circulation and thereby modulates pulsatile secretion of LH has been recognized as a key determinant of the reproductive function in mammals. Thus, various internal, as well as external, factors first modify the electrical activity of the GnRH pulse generator, which then alters the pulsatile pattern of gonadotrophin secretion and eventually influences reproductive functio...

Summary. During pregnancy the hypothalamic–hypophysial axis is suppressed by the high concentrations of progesterone and oestradiol in the circulation. The high concentrations of these steroids appear to inhibit secretion of GnRH from the hypothalamus, resulting in inadequate stimulation of pituitary gonadotrophs to maintain synthesis of LH. This produces a depletion of LH in the anterior pituitary gland that must be restored after parturition before nor...

It has been suggested that the long-term reproduction of the sow is best served by minimizing weight and fat loss in lactation. Such a strategy would require only a minimal restoration of weight in the following pregnancy, which would be beneficial, since the greater feed intake and weight gain in pregnancy, the greater the weight loss in lactation. Feeding ad libitum should be practised during lactation while gestation feed intake must be held low. A relationship between...

Summary. 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 conf...

Summary. Follicular heterogeneity has been demonstrated in both naturally cyclic and PMSG-stimulated immature gilts in that follicles in the selected ovulatory population differ in size by up to 2 mm and show marked variability in steroid content and gonadotrophin binding ability. This biochemical and morphological asynchrony continued into the immediate preovulatory phase and changes in response to the LH surge did not always occur simultaneously even in...

Manipulation of the pig genome is currently restricted to the random insertion of new DNA using pronuclear microinjection. This method suffers from a number of inherent limitations, the majority of which result from the inability to control the site at which the transgene becomes integrated. These drawbacks, together with the need to be able to target existing genes, will result in the replacement of pronuclear injection by new methods that have the capability to direct i...

Keywords: counter current transfer; ovary; oviduct; uterus; pig© 1990 Journals of Reproduction & Fertility Ltd...

It is well established that the interferon τ (IFN-τ) family of proteins play a major role in preventing the regression of the corpus luteum during early pregnancy in ruminants, such as cattle, sheep and goats, but not in other mammals. These interferons, which are structurally and functionally related to type I interferon, such as IFN-α and -ω, arose from a duplication of an IFN-ω gene approximately 36 million years ago. The IFN-τ genes have conti...

Development of the corpus luteum (CL) in ruminants occurs in a rapid and time-dependent manner within 1 week after ovulation, with morphologic and biochemical changes in the cells of the theca interna and granulosa cells of the preovulatory follicle. These changes involve luteinisation of steroidogenic cells and angiogenesis to establish normal luteal function (progesterone secretion). The CL is composed of a large number of vascular endothelial cells, large and small steroido...