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Reproduction in Domestic Ruminants III

Reproduction in Domestic Ruminants III

Environmental and Metabolic Interactions

bp0003rdr30 | Environmental and Metabolic Interactions | REDR1994

Endocrine basis for puberty in heifers and ewes

Kinder JE , Bergfeld EGM , Wehrman ME , Peters KE , Kojima FN

Maturation processes that culminate in puberty and sexual maturity are initiated before birth, continue through prepuberty (> 50 days before puberty) and peripuberty (50 days before puberty) and are completed early after puberty. The hypothalamus is the primary site of change during transition to sexual maturity. Maturation of the hypothalamus results from decreased negative feedback of oestradiol that leads to increased frequency of release of LH pulses. Increased tonic r...

bp0003rdr31 | Environmental and Metabolic Interactions | REDR1994

Involvement of thyroid hormones in seasonal reproduction

Karsch FJ , Dahl GE , Hachigian TM , Thrun LA

This article reviews experiments performed to investigate the importance of thyroid hormones to the expression of the seasonal reproductive cycle of ewes. Thyroidectomy was found to block the transition from the breeding season to anoestrus and to cause ewes to exhibit oestrous cycles all year round. Mechanistically, thyroidectomy produced this effect by preventing the seasonal increase in responsiveness to the negative feedback action of oestradiol on episodic GnRH secretion,...

bp0003rdr32 | Environmental and Metabolic Interactions | REDR1994

Melatonin binding sites and their role in seasonal reproduction

Kennaway DJ , Rowe SA

The pineal gland has a major role in the translation of scotophase duration into a hormonal signal by the hormone melatonin. Animals such as sheep, goats and deer use the seasonal variation of this signal to coordinate reproductive behaviour with the environment. Despite intensive research over more than 30 years the site(s) of action of melatonin and the resultant intracellular responses are still not clear. This review discusses recent work that has localized the site of act...

bp0003rdr33 | Environmental and Metabolic Interactions | REDR1994

Nutritional influences on reproduction in mature male sheep and goats

Martin GB , Walkden-Brown SW

Changes in the nutrition of mature rams and goat bucks lead to profound responses in testicular size and therefore the rate of production of spermatozoa. These effects are largely due to changes in the size of the seminiferous tubules and in the efficiency of spermatogenesis. With the exception of severe undernutrition, the effects on spermatogenic function are not accompanied by similar changes in endocrine function of the testes, as measured by the production of testosterone...

bp0003rdr34 | Environmental and Metabolic Interactions | REDR1994

Stress and reproduction in farm animals

Dobson H , Smith RF

Transport of post-partum cows or sheep before an oestradiol-induced LH surge delayed gonadotrophin secretion possibly by affecting hypothalamic activity but not via an opioid mediated mechanism as the effect could not be reversed by naloxone. In addition, reduced LH responses to GnRH were observed in cattle during transport. In sheep, adrenocorticotrophic hormone (ACTH) also diminished the LH response to GnRH, but only when GnRH was administered 3 h after ACTH, not after 0.5 h...

bp0003rdr35 | Environmental and Metabolic Interactions | REDR1994

Sensory and behavioural control of gonadotrophin secretion during suckling-mediated anovulation in cows

Williams GL , Griffith MK

A major limiting factor in the resumption of postpartum ovarian cycles in cattle is the inhibitory influence of the suckling calf on central regulatory elements controlling the release of GnRH from the median eminence. This inhibitory influence occurs only as a consequence of specifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally using thermal, electrical or mechanical stimuli, and is not de...

bp0003rdr36 | Environmental and Metabolic Interactions | REDR1994

Physiological effects of undernutrition on postpartum anoestrus in cows

Jolly PD , McDougall S , Fitzpatrick LA , Macmillan KL , Entwistle KW

The focus of this review is the physiological effects of undemutrition on ovarian follicle growth and the occurrence of ovulation in postpartum cows. Evidence suggests that moderate levels of underfeeding, before or after calving, may interfere with the mechanism(s) of final follicle maturation and ovulation, whereas more pronounced nutritional deficiencies may affect the mechanism(s) regulating dominant follicle size and the dynamics of dominant follicle growth and regression...

bp0003rdr37 | Environmental and Metabolic Interactions | REDR1994

Factors that affect fertility during oestrous cycles with short or normal luteal phases in postpartum cows

Inskeep EK

We have used a model to study infertility in postpartum cows. In mated cows with short luteal phases, daily supplementation with progestagen, beginning on day 3, failed to maintain pregnancy, despite the fact that fertilization, early embryo development and transport of the embryo into the uterus appeared to be normal. Normal embryos were transferred, on day 7 after oestrus, into cows with short luteal phases that received daily supplementation with progestagen, and embryos fr...