Bioscientifica Proceedings

The inconsistency of data from experiments designed to show nutritional effects on embryonic survival is perplexing. However, a number of experimental models have provided some insight into the mechanisms that potentially mediate interactions between nutrition, metabolic state and embryonic survival. The developing ovarian follicle provides the maturational environment for the oocyte, and differences in follicular maturation are associated with differences in the ability ...

Sex ratios that deviate from 1:1 have been observed in response to a number of stimuli. In this review we will discuss sex ratio biasing, and the evolutionary and molecular mechanisms thought to underlie this phenomena in mammals. The role of embryo quality will be discussed in relation to sex ratio modulation and epigenetic programing of the embryo. Sex ratio skewing has been studied in many species and several factors have been proposed as influencing secondary sex rat...

Follicle-stimulating hormone (FSH) is a key hormone in the regulation of follicular development. Although the existence of FSH heterogeneity is well established, the physiological significance of this pleomorphism remains unknown. Observed changes in circulating FSH heterogeneity during critical reproductive events such as puberty and reproductive cyclicity suggest that different combinations of FSH isoforms reach the target sites during different physiological states to influ...

The neuroendocrine regulation of GnRH secretion plays a central role in timing gamete release in both sexes. This regulation is more complex in the female because the discontinuous release of ova is more complex than the continuous release of spermatozoa. This review provides an evolving understanding of the sex differences in reproductive neuroendocrine controls and how these differences arise. The rules for sexual differentiation of steroid feedback control of GnRH secretion...

Implantation/placentation in domestic pigs is preceded by synthesis ot oestrogen by the conceptus to maintain functional corpora lutea throughout pregnancy and a rapid morphological transformation of conceptuses from spherical to long filamentous thread-like structures. Initial conceptus expansion, reaching a metre in length, not only delineates the surface area for placental attachment, but also provides the mechanism for delivery of oestrogen to signal events necessary ...

Summary. Theca cells are essential for female reproduction being the source of androgens that are precursors for follicular oestrogen synthesis and also signal through androgen receptors (AR) in the ovary and elsewhere. Theca cells arise from mesenchymal cells around the secondary follicle stage. Their recruitment, proliferation and cytodifferentiation are influenced, directly or indirectly, by paracrine signals from granulosa cells and oocyte although uncerta...

Summary. Tests for the detection of pregnancy early after insemination have not yet reached their full potential. Currently, the milk progesterone assay provides the earliest possible test, at an interval of one oestrous cycle after insemination, i.e. 17, 21 and 21 days in sheep, goats and cows respectively. This assay is pregnancy non-specific and rate of detection of pregnant animals is acceptable but less than desirable.Detection of a...

Keywords: lactation; weaning; sow; endocrinology; suckling© 1990 Journals of Reproduction & Fertility Ltd...

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...

Enhanced secretion of PGF2α from endometrial explants in vitro in response to oxytocin is associated with augmented activities of phospholipase A2, phospholipase C and prostaglandin endoperoxide H synthase (PGS). In early pregnancy, maintenance of the corpus luteum is associated with an absence of pulsatile PGF2α secretion; an increase in endometrial inhibitors of phospholipase A2 and PGS contribute to the antilute...