Bioscientifica Proceedings

Summary. An inadequate luteal phase occurs in domestic ruminants in several physiological situations (e.g. puberty, post partum), and also following the induction of ovulation in anoestrous ewes with GnRH treatment. The induced corpora lutea (CL) initially developed, but then regressed rapidly after Day 4, unless the animals had been primed with progesterone before GnRH therapy or hysterectomized. Significant increases in prostaglandin F-2α metab...

Abstract unavailable© 1982 The authors...

Abstract unavailable© 1990 Journals of Reproduction & Fertility Ltd...

The mechanisms controlling the follicular growth continuum in the pig involve the interaction between local growth factors which are expressed throughout development and extra-follicular factors such as gonadotrophins. A large number of follicular growth factors, many belonging to the transforming growth factor-β (TGF-β) superfamily, have been identified in the somatic cells and in the oocyte. The relative importance of these intra-follicular factors varies wit...

Abstract unavailableKeywords: corpus luteum; sheep; protein kinase C; calcium; phosphoinositide turnover© 1991 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...

Summary. The pig is an excellent animal in which to study the control of folliculogenesis in a polytocous species, and particularly to examine the inter-relationships between follicles from the same animal. Follicle recruitment occurs from the proliferating pool, and various studies suggest that this recruitment occurs between Days 14 and 16 of the oestrous cycle. The growth of follicles selected for ovulation is associated with rapid atresia of smaller f...

The enhanced early embryonic survival in Chinese Meishan compared with Large- White gilts may be due, in part, to differences in ovarian and endocrine function, particularly during the periovulatory period. The overall patterns of oestradiol, LH and FSH secretion were not different between Meishan and Large-White hybrid controls during this period, although circulating inhibin concentrations were higher in Meishan gilts. Thus, there appeared to be a decreased sensitivity ...

Cattle have recurrent follicular waves every 7–10 days in most physiological situations; an FSH increase is associated with emergence of the wave and LH pulse frequency determines the fate of the dominant follicle. To control oestrus with hormones it is necessary to ensure that either induced corpus luteum regression or the termination of a progestogen treatment coincides with the selection of the dominant follicle during the wave, to give a precise onset of oestrus and ...

Early pregnancy is maintained in ruminants through the actions of conceptus-derived interferon (IFN)-tau on the endometrium. IFN-tau alters uterine release of PGF2α, which results in rescue of the corpus luteum and continued release of progesterone. The mechanism of action of IFN-tau includes inhibition of oestradiol receptors, consequent reduction in oxytocin receptors, activation of a cyclooxygenase inhibitor, and a shift in the PGs to favour PGE2 ...