Bioscientifica Proceedings

Summary. Development of the corpus luteum (CL) is vital for the early increase in postovulatory progesterone that drives embryo development and the successful establishment of pregnancy. Following ovulation, rapid and dramatic cellular reorganisation and intense angiogenesis are required to support the timely transition to progesterone secretion. In addition to inherent physiological challenges, this process is sensitive to any imbalance in metabolism or healt...

The release of GnRH from nerve terminals in the median eminence into the portal vessels is influenced by factors in the internal and external environment of the animal. In the former category are the gonadal steroid hormones oestrogen and progesterone which alter the characteristics of GnRH secretion during the oestrous and seasonal cycles. These cannot exert their actions directly on the GnRH neurones as they do not possess hormone receptors. Therefore, some other steroid-sen...

Abstract unavailable© 2003 Society for Reproduction and Fertility...

Abstract. During the last decade, transcriptome profiling has emerged as an efficient approach to describe and study cellular functions. The potential to survey transcript abundance for all genes offers promise to shed light on mammalian early embryogenesis. Furthermore, the report of aberrant phenotypes following the application of reproductive technologies also fueled the need to understand how embryos react, cope and adapt to their surrounding microenvironm...

In mammals, growing oocytes have characteristically high levels of RNA synthesis. After the initiation of meiosis, that is germinal vesicle breakdown, this RNA synthesis ceases. Although there is limited evidence for RNA synthesis by the zygote, significant amounts of RNA synthesis do not occur until a species-specific cell stage. In pigs, significant amounts of mRNA synthesis cannot be detected before the four-cell stage. There appear to be three qualitatively different ...

The second week of pregnancy is a particularly critical period for embryonic survival in pigs. Within that time, conceptus oestrogen synthesis is initiated, spacing and final placement of conceptuses is completed, and the signal for extending the functional lifespan of the corpora lutea is received by the mother. There is also a marked increase in blood flow to the uterus and the uterine endometrium produces and secretes nutrient histotrophe. Coneeptus-derived oestrogen h...

During early pregnancy the bovine embryo must produce a protein called interferon τ which inhibits the development of the luteolytic mechanism. Failure to inhibit luteolysis is the major cause of pregnancy loss in cows. The embryo must produce sufficient quantities of interferon τ by about day 16 to prevent luteolysis. Its ability to achieve this is largely dependent on the pattern of maternal progesterone production. A late rise in progesterone after ovulation or po...

Exposure of Ihe sheep fetus to testosterone from day 30 to day 90 of a 147 day gestation causes the neurones that control GnRH secretion, the GnRH neuronal network, to become organized in a sex-specific manner. After androgen exposure in utero, GnRH neurones are activated in a sexually differentiated pattern by gonadal steroid hormones. Specifically, follicular phase concentrations of oestrogen trigger a GnRH 'surge' in ewes, but not in rams or females treated...

Buffalo are of high economic importance for farmers in several developing countries but reproductive performance is poor. A large proportion of heifers attain puberty at 3–5 years of age. A good quality diet supplemented with extra nutrients reduces the age of puberty whereas the effects of administration of exogenous GnRH or equine chorionic gonadotrophin (eCG) are equivocal. The incidence of anoestrus in buffalo ranges from 20 to 80% depending on season. Most buffal...

Prenatal mortality in European pigs is estimated at 30-40%, the majority of which occurs between days 12 and 18 after mating. Chinese Meishan pigs are prolific, averaging three to five more pigs per litter than do European breeds. Early reports into the fecundity of Meishan females suggested that their prolificacy resulted from lower embryonic mortality when compared with European females exhibiting the same ovulation rate. The preponderance of evidence suggests that ther...