Bioscientifica Proceedings

Summary. Identical twin pairs of dairy cows (one twin being placed with 4 calves for multiple suckling while the other was machine milked) were used to study the hormonal changes associated with anoestrus. Experiments were conducted to examine the effect of multiple suckling on the interval to first oestrus post partum, concentrations of LH and progesterone post partum, and the LH response to LH-RH or oestradiol-17β. The effects of hormo...

Summary. In the ram, changes in daylength influence testicular activity by modifying the release of luteinizing hormone-releasing hormone (LH-RH) and thus the gonadotrophins. To investigate the nature of this response the hourly fluctuations in the circulating levels of prolactin, luteinizing hormone (LH) and melatonin were measured in rams kept under various artificial lighting conditions.In Exp. 1, 8 Soay rams (4 control and 4 from whi...

Summary. Neuroendocrine events before puberty are compared in male and female cattle, sheep and pigs. The patterns of secretion of gonadotrophin, the age-related LH responses to castration or LH-RH administration and the effects of prolonged steroid treatment give information about the maturity of the hypothalamic-pituitary axis. It appears that in all three species the mechanisms involved in the expression of puberty are progressive rather than abrupt events....

Summary. The control and induction of ovulation in cattle are discussed with particular reference to use of progesterone-impregnated coils in heifers and beef cows. Progesterone treatment for 14 days was required to obtain precise onset of oestrus. With 7, 9 or 12 days of progesterone treatment a luteolytic agent in the form of a prostaglandin (PG) or oestradiol benzoate had to be used. Fertility was normal after treatment durations of 7, 9 or 12 days, but fer...

Inhibin, activin and follistatin are protein hormones with diverse physiological roles. The involvement of inhibin in the regulation of pituitary FSH production and secretion in adult males and non-pregnant females is well established. However, it is unlikely that inhibin plays a similar role in pregnancy in ruminants. Inhibin and activin molecules show a high degree of structural similarity to potent growth and differentiation factors of the transforming growth factor β ...

The development of nuclear transfer from tissue culture cells in livestock made it possible in principle to produce animals with subtle, directed genetic changes by in vitro modification of nuclear donor cells. In the short period since nuclear transfer was first performed, gene targeting in livestock has become a reality. Although gene targeting has immediate potential in biotechnology, it is unclear whether there are practical agricultural applications, at present. ...

Summary. Synthesis of biologically active LH is complex, due in part to its hetero-dimeric subunit structure and to the numerous post-translation modifications of each subunit. Through the use of mammalian expression vectors we have been able to introduce the bovine α subunit and LH-β genes into a Chinese hamster ovary cell line deficient in dihydrofolate reductase. The bovine genes are actively expressed and the Chinese hamster ovary cells secrete b...

Summary. Several manipulation techniques including nuclear injections, nuclear transplantation, embryo splitting, chimaera production and sperm injection are discussed with special reference to their application in the pig. The nuclear injection technique is likely to be of greatest use for gene transfer. Gene transfer is feasible for pig embryos. but it is very inefficient. Efficiencies of various steps in the successful production of transgenic offsprin...

Keywords: pig; models; metabolism© 1990 Journals of Reproduction & Fertility Ltd...

Keywords: counter current transfer; ovary; oviduct; uterus; pig© 1990 Journals of Reproduction & Fertility Ltd...