Bioscientifica Proceedings

Litter size is often proposed as the trait that could have the greatest impact in improving reproductive efficiency of pigs. Efforts to select directly for increased litter size have generally been unsuccessful and highly variable. As a result, several attempts have been made to identify critical physiological components that control litter size, with the underlying assumption that augmenting these components would improve this important trait. One attempt at improving p...

The field of livestock genomics has made considerable advances in the past decade. In the area of pig reproduction, a number of genome scans have identified several genomic regions associated with variation in reproductive measures ranging from ovulation rate, litter size and testis size. Additionally, several candidate genes have been associated with variation in litter size. These studies primarily focused on developing genetic markers to facilitate selection decisions...

The autocrine and paracrine role of the insulin-like growth factors (IGFs) and epiderrnal growth factor (EGF)-related peptides in pig ovary are reviewed. For convenience, each of these regulatory systems is divided into several interactive components: regulated expression of the growth factors, growth factor reception at the cell surface and intracellular action of the growth factors. In addition, the concept of regulated bioavailability and targeting of growth factors in...

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. ...

Overview. One of the most fundamental axioms of mammalian reproduction is that pregnancy requires the support of progesterone without which it cannot be established or maintained. Though this basic physiological tenet was accepted long ago, major gaps in our understanding of the physiology of both pregnancy and parturition remain which hamper our ability to solve clinically and agriculturally significant problems such as low fertility, fetal growth restriction...

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