Bioscientifica Proceedings

During the past 12 years, ruminants have provided a focus for some significant advances in mammalian reproductive biotechnologies. Lambs were the first offspring generated after nuclear transfer of fetal or adult cells to enucleated oocytes, and many calves of pre-determined gender are today the result of commercialized semen sexing. In 1990, the birth of one calf provided living proof that even 'dead' spermatozoa can be paternal, whereas, more recently, a short-lived ...

Abstract unavailable© 2009 Society for Reproduction and Fertility...

Timing of conceptus growth and attachment to the uterine luminal epithelium is regulated by progesterone secretion from the corpus luteum and by expression of progesterone receptor in the uterine epithelia and stroma. Conceptus growth and uterine attachment are temporally associated with the disappearance of progesterone receptors from uterine epithelia. While the loss of progesterone receptor from the endometrial epithelia on day 10 of the oestrous cycle and pregnancy h...

Abstract unavailable© 2009 Society for Reproduction and Fertility...

Summary. During folliculogenesis a group of growing preantral follicles becomes responsive and dependent upon gonadotrophins, especially FSH, for their continued growth and differentiation. However, most of these follicles undergo atresia. The mechanisms that result in survival of a specific number of ovulatory (dominant) follicles appear to depend upon: (a) responsiveness of preantral follicles to gonadotrophins, (b) inhibitory and stimulatory factors from a ...

Summary. Behaviour in pigs is sexually dimorphic as early as 1 month of age; mounting of penmates is observed more frequently for males than for females. This mounting reaches its highest frequency during the 2nd month of life and then declines to a low frequency in prepubertal pigs. During the prepubertal period (3-5 months of age), bipotentiality of sexual behaviour is apparent in boars because they will not only mount oestrous females but they are also...

Summary. Seasonal variations of reproductive ability have been demonstrated in male and female sheep and goats. For the female, there is a distinct breeding season. Whilst there are large breed differences in the duration of the sexual season, oestrous cycles generally start when daylength is decreasing and end when daylength is increasing. In some breeds, ovulation without oestrus occurs during the non-breeding season. Although males are able to mate all the ...

Summary. Prolactin and LH are required for the maintenance of normal luteal structures during early pregnancy in the ewe, whilst luteolysis, induced by prostaglandin F-2α is inhibited by the presence of the conceptus. The trophoblast also secretes a local anti-luteolytic factor, trophoblastin, which is most probably a protein because it is thermolabile and inactivated by pronase. It is soluble at pH 9.6 and can be separated on Ultrogel. Trophoblastin is p...

The hypothalamo–pituitary–gonadotrophic axis develops in the sheep fetus from midgestation to late gestation. The GnRH neuronal centres seem to be fully developed in the fetus and their localization complies with the adult pattern. Pituitary gonadotrophs are responsive to exogenous GnRH and release LH and FSH in a pulsatile fashion; the highest concentrations in plasma are found during late gestation. In sheep, maturational changes of this axis continue through to ...

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