Bioscientifica Proceedings

As stated in the first Proceedings, the economically important domestic species have been the subject of ongoing reproductive research over many decades. The aims of researchers and clinicians have been directed at increasing fecundity and fertility, to manipulate reproduction for simpler management, to increase the genetic influence of selected individuals and importantly to improve animal welfare. A group of international researchers initiated the first symposium in Australi...

Abstract unavailable© 1981 Journals of Reproduction & Fertility Ltd...

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 ...

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. 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. In the ram, the size of the testes is related to the concentrations of FSH, LH and testosterone in the blood. A significant linear relationship is observed between testicular size and the level of FSH until a maximum after which no further increase in testis size is observed. Testicular size is also linearly related to the mean level (25 consecutive hours of sampling) of LH and testosterone in the blood, with apparently no upper limit, and to the freq...

Summary. In Exp. 1, sheep fetuses (2 male and 3 female) were gonadectomized between Days 70 and 120 of gestation and their blood LH and FSH levels were compared to those of control animals (4 male, 6 female) at regular times during the first year after birth. In Exp. 2. fetuses (3 male and 5 female) were gonadectomized between Days 50 and 60 of gestation and gonadotrophin levels at Day 90 of gestation were compared to those of control fetuses of the same age. ...

Summary. In calves made cryptorchid at birth, serum LH concentrations were elevated (P < 0.01) over those of intact controls by 7 weeks of age; a difference which persisted until after puberty. When intact and cryptorchid bulls were given LH-RH, i.v., at approximately 18 months of age, cryptorchid bulls were more responsive. Serum LH concentrations (mean ± s.e.m.) after 250, 1000 and 4000 ng LH-RH were 0.2 ± 0.03, 1.2 ± 0.3 and 12.1...

Summary. It is proposed that the first follicular phase in the lamb is initiated when responsiveness to oestradiol inhibition of LH secretion decreases sufficiently to permit the expression of an inherent hourly LH pulse rhythm. The hourly LH pulse rhythm is believed to drive oestradiol production to levels that induce the first LH surge. This hypothesis is based upon several considerations. First, pulsatile LH secretion invariably occurs at low frequencies in...

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. In four studies secretion patterns of LH, FSH, prolactin, testosterone and progesterone were measured in male and female cattle to determine endocrine changes associated with sexual maturation. Two periods of increasing gonadotrophin secretion were observed, the second one coinciding with puberty. A short luteal phase of 8–12 days precedes the first oestrus at 10–11 or 14 months of age. The testosterone values of the bulls increased with age...

Summary. The relationship between the pituitary gland and testis in rams was studied from birth to sexual maturity. The concentrations of LH, FSH and testosterone increased between 5 and 7 weeks of age; the rise was not correlated with any specific cytological change in the testis. An augmented pituitary response to LH-RH was demonstrated as levels of gonadotrophin increased. It is unclear whether this change in sensitivity plays a role in initiation of the pu...

Summary. In the adult non pregnant ewe the secretion of FSH is sufficient to ensure a continuous growth and development of antral follicles to 3–5 mm size at all times. Further development and increased secretion of oestradiol through the final 72 h to ovulation depends on adequate stimulation by LH. During anoestrus and the luteal phase of the cycle LH pulses occur too infrequently to stimulate sufficient oestradiol to evoke an LH surge. Moreover, during...

Summary. In the sheep the total duration of folliculogenesis, i.e. from the start of development of a primordial follicle to ovulation, is thought to be about 6 months. The initiation of follicular growth as follicles enter the growth phase is influenced by gonadotrophins and, in the sheep, by factors such as breed, season and nutrition. Preantral follicles are characterized by a slow growth rate and no atresia. The number of preantral follicles is influenced ...

Summary. Studies of isolated cell types from sheep follicles revealed several functional changes which occur during follicular maturation. Cyclic AMP production by granulosa cells from the smallest follicles studied (1–3 mm diameter) was stimulated by FSH but not by hCG, suggesting functional FSH receptors at this early stage of differentiation. Medium-sized follicles (4–6 mm) responded to both FSH and hCG. Granulosa cells were unable to synthesize a...

Summary. Milked dairy cows generally have a shorter post-partum interval to ovarian cyclicity than suckling dairy or beef cows. In milked and suckling cows, there is a strong seasonal influence with spring-calving cows remaining anoestrous longer. Increasing the suckling intensity further delays the onset of ovarian cyclicity, probably by increasing the frequency or strength of its inhibitory influence on hypothalamic activity. Plasma FSH levels rise in most c...

Summary. This review analyses the endocrine recognition of pregnancy in the sheep. Particular emphasis is placed on the effect of a blastocyst on prostaglandin and protein metabolism in the endometrium. The preimplantation period is associated with increased prostaglandin content in the endometrium and uterine lumen, increased leucine incorporation into endometrial protein and increased blood flow to the uterus. It is concluded that there are substantial alter...

Abstract unavailable© 1981 Journals of Reproduction & Fertility Ltd...

Summary. The appearance and production of an early pregnancy factor (EPF) has been studied in sheep and cattle. This factor can be detected in serum and tissues of pregnant animals by its synergistic action with antilymphocyte serum in reducing the number of rosettes formed in a rosette inhibition test. The range of the rosette inhibition titre for serum from non-pregnant animals was 4–10. Values higher than these were considered to indicate the presence ...

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...

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...

Summary. When clover-infertile ewes are subsequently exposed to non-oestrogenic pasture, they have a reduced fertilization rate, due to an inability to store spermatozoa in the cervix, and the cervical mucus has a reduced spinnbarkeit, caused by a slower response to oestrogenic stimulation. Vaginal cell keratinization and oestrous behaviour occurred more slowly after treatment of affected ewes with oestrogen. Other changes in affected ewes suggest that phyto-o...

Summary. Results of a detailed study involving 18 pregnant, 17 cyclic and 12 inseminated but non-pregnant Holstein heifers indicated the following. (1) Jugular plasma progesterone concentrations were higher (P < 0.05) in pregnant than in cyclic or in inseminated–non-pregnant animals from Days 10 through 18. (2) Jugular plasma progesterone concentrations of inseminated–non-pregnant animals could be related to heifers in which (a) fertiliz...

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...