Bioscientifica Proceedings

Abstract unavailable© 2013 Context Products Ltd...

Summary. Ultrasound imaging has shown that cattle exhibit 2 or 3 waves of follicular development during an oestrous cycle. The waves consist of the contemporaneous appearance, about every 7 days, of a group of follicles ≥ 5 mm in diameter. One follicle gradually becomes larger than the rest (i.e. dominant). There are several lines of evidence suggesting that the waves occur regularly under conditions of basal LH and FSH. (1) Cycles with 3 waves of follic...

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. Sheep betaretroviruses offer a unique model system to study the complex interaction between retroviruses and their host. The sheep genome contains 27 endogenous betaretroviruses (enJSRVs) related to the exogenous and pathogenic Jaagsiekte sheep retrovirus (JSRV), the ca...

Summary. Sexual maturation in cows and ewes is modulated through changes in hypothalamic inhibition. This inhibition results in little or no stimulation of the release of gonadotrophins from the anterior pituitary. The ovary has a primary role in inhibiting gonadotrophin secretion during the prepubertal period and the responsiveness to the negative feedback effects of oestrogen decreases during the peripubertal period. There is also an increased secretion of o...

Summary. Important improvements in the management of sows have been made over the past 20 years in Europe and the U.S.A. Nevertheless, annual productivity varied between 15 and 25 piglets weaned per sow per year in France for 1983. Reasons for such a difference in productivity have been analysed quantitatively.Marked differences exist between herds in the genotype of pig used and in the age of puberty. Transportation acts as a stress...

Keywords: boar exposure; puberty; gilts; pheromones© 1990 Journals of Reproduction & Fertility Ltd...

In vitro culture has provided new information on the mechanisms involved in fertilization where two completely different cells fuse together. At the same time, results obtained in vitro have led to new questions. Does the follicle influence the final maturation process of the oocyte and does the oviduct regulate the normal behaviour of spermatozoa? Recent studies indicate a critical influence of both the follicular compartment and the oviduct on the norm...

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...

The enhanced early embryonic survival in Chinese Meishan compared with Large- White gilts may be due, in part, to differences in ovarian and endocrine function, particularly during the periovulatory period. The overall patterns of oestradiol, LH and FSH secretion were not different between Meishan and Large-White hybrid controls during this period, although circulating inhibin concentrations were higher in Meishan gilts. Thus, there appeared to be a decreased sensitivity ...

During the period of late follicular development and the first four days of the oestrous cycle, the oviduct occupies a central role in the establishment of pregnancy. Oviductal function is regarded as being either 'passive' or biologically active, providing an environment that sustains and enhances fertilization and early cleavage-stage embryonic development. Recent reports have focused on this microenvironment and shown that ovarian steroids induce marked morphological, ...