Bioscientifica Proceedings

Embryonic diapause was first identified over 150 years ago, but many questions still remain about how the external and hormonal controls of embryonic diapause translate into how the uterus conveys information to the embryo. Current evidence suggests that the control of diapause is mediated by components of the uterine secretions. However, the identity of the essential signalling molecule(s) is unknown. The mouse (Mus musculus), the mink (Neovison vison) and t...

Mammalian embryonic diapause is a reproductive phenomenon defined by the reversible arrest in blastocyst development and metabolic activity within the uterus which synchronously becomes quiescent to implantation. This natural strategy, evident in over 130 species across eight orders, can temporally uncouple conception from delivery until conditions are favorable for the survival of the mother and newborn. While the maternal endocrine milieu has been shown to be important for t...

Summary. European breeds of rams appear to be responsive to photoperiodic changes even though there are large differences between breeds in the timing and amplitude of endocrine (LH and testosterone) and gametogenetic variations before the sexual season. Light regimens such as 6-month light cycles or alternations of constant short and long days every 12–16 weeks are able to entrain the parameters of sexual activity. In these regimens in which the period ...

There are many potential applications of transgenic methodologies for developing new and improved strains of livestock. One practical application of transgenic technology in pig production is to improve milk production or composition. The first week after parturition is the period of greatest loss for pig producers, with highest morbidity and mortality attributed to malnutrition and scours. Despite the benefits to be gained by improving lactation performance, little prog...

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...

Summary. The life time reproductive performance of 2 flocks of Merino crossbred ewes pinealectomized at 7–60 days of age, and maintained in South Australia did not differ from that of sham-operated control animals kept in the same flocks. The pineal gland is therefore not a major determinant of reproductive success, but a role for the pineal in adjusting breeding activity to season is not excluded. It was confirmed that pineal denervation of adult ewes ...

Abstract unavailable© 1987 Journals of Reproduction & Fertility Ltd...

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...

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...