Environmental control of seasonal breeding: a common final mechanism governing seasonal breeding and sexual maturation

Karsch, Fred J.; Foster, Douglas L.

doi:10.1007/978-1-349-03964-7_3

Cited by 13 publications

(6 citation statements)

References 92 publications

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“…It is likely therefore that the plasma concentrations of oestradiol-17P measured in the present study exert a negative feedback action on pituitary LH secretion, thereby preventing the final maturation of ovarian follicles and secretion of oestradiol-17|3 at the high levels typical of oestrus and the preovulatory period (Glencross, Esslemont, Bryant and Pope, 1981). Such a mechanism has been proposed for pre-pubertal sheep (Karsch and Foster, 1981).…”

Section: Therementioning

confidence: 83%

A note on the concentrations of plasma oestradiol-17β and progesterone around the time of puberty in heifers

Glencross¹

1984

Anim. Sci.

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In heifers, plasma progesterone levels were low (<0-3 |xg/l) from the 59th to about the 15th day before puberty (defined as the day when oestrus was first detectable by the fern pattern of dried cervical mucus). Plasma oestradiol-17P levels varied randomly within the range 1 to 4 ng/1 over the same period, but then showed three peaks of about 6, 9 and 4 ng/1, respectively 8 days before puberty, on the day of puberty and 4 days later. The pre-pubertal oestradiol-17p peak was followed by a short period of elevated progesterone levels. Whether this oestradiol-17P peak induced ovulation is uncertain; it is however clear that a corpus luteum of normal life-span was not formed. The oestradiol-17p peaks on the day of puberty and 4 days later, when progesterone levels were rising rapidly, were typical both in magnitude and duration of those occurring before and after ovulation in post-pubertal oestrous cycles.

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Section: Therementioning

confidence: 83%

A note on the concentrations of plasma oestradiol-17β and progesterone around the time of puberty in heifers

Glencross¹

1984

Anim. Sci.

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“…Sensitivity to testosterone in some wethers may also have been influenced by the photo¬ period (Pelletier & Ortavant, 1975;Parrott & Davies, 1979). Experiment 2 was carried out in early winter when the hypothalamo-pituitary axis in sheep be¬ comes increasingly sensitive to steroid negative feed¬ back (Karsch & Foster, 1981). This change in sensi¬ tivity, plus the fact that the implants used provided serum testosterone concentrations which approxi¬ mated mean concentrations observed in Merino rams during the seasonal peak in testosterone secretion (D'Occhio & Brooks, 19836), might explain the sensi¬ tivity to testosterone of some wethers.…”

Section: Discussionmentioning

confidence: 99%

Differential effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour in rams

D’Occhio¹,

Galil²,

Brooks³

et al. 1985

Journal of Endocrinology

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Castrated sheep were used to study the effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. In the first experiment serum LH and FSH concentrations were determined in intact rams, recently castrated (2 days and 3 weeks) and long-term castrated animals (greater than 2 years, wethers) during intravenous testosterone infusion at physiological and supraphysiological levels. In intact rams, testosterone infusions effectively suppressed serum LH whilst FSH levels were suppressed only after prolonged infusion at the supraphysiological dose. Recently castrated sheep, which had higher gonadotrophin levels than intact rams, were less sensitive to testosterone feedback. Neither rate of testosterone infusion had any effect on the raised gonadotrophin levels in wethers. In a second experiment gonadotrophin concentrations and mating behaviour were determined in wethers bearing subdermal polydimethylsiloxane implants of testosterone, dihydrotestosterone and oestradiol. Testosterone implants stimulated mating behaviour in all wethers but suppressed gonadotrophins in only a proportion (three out of seven) of the animals. Both oestradiol and dihydrotestosterone suppressed LH and FSH in all wethers, whilst oestradiol, but not dihydrotestosterone, also stimulated mating behaviour. The present findings indicate that testosterone imposes continuing negative feedback on gonadotrophin secretion and that changes in the gonadotrophin regulatory system, which lead eventually to a loss in sensitivity to testosterone feedback, develop soon after gonadectomy. The results also provide the first direct evidence that longterm gonadectomy in male sheep has differential effects on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Photoperiod is the most important environmental zeitgeber for thermogenesis (Heldmaier, Steinlechner & Rafael, 1981), energy use (Dark & Zucker, 1983), circadian rhythms of locomotor activity (Daan & Aschoff, 1975), reproduction (Reiter, 1981;Karsch & Foster, 1981) and other cycles in mammals. In Meles meles, photoperiod is the main controlling factor in the timing of delayed implantation (Canivenc & Bonnin, 1979).…”

Section: Environmental Influencesmentioning

confidence: 99%

Overwintering strategies of the badger, Meles meles, at 57 °N

Fowler

Racey

1988

Journal of Zoology

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With 7 figures in the text)Over two eight-month periods (October/November-May) during successive winters (1983/4 and 1984/5), the body temperatures and activity patterns of captive badgers, Meles rneles, living under semi-natural conditions, were studied at 57 "N in Scotland. Temperature-sensitive radio transmitters and automated telemetry systems provided long-term records of body temperatures and times badgers were absent from an artificial sett.Badger body temperatures of 28-34 "C, significantly below euthermic levels, were recorded between October/November and March each winter, with differences between mean daily maxima and minima varying from 1.6 to 8.9 "C. This was associated with a reduction, by up to 90%, in the time that the badgers spent outside their sett in mid-winter. Body temperatures did not show circadian cyclicity, but from February onwards most locomotor activity occurred between 22:OO and 02:OO GMT. The extent to which activity was concentrated around midnight increased with decreasing night length in spring.The body temperatures of one female badger fell to a nadir of 28 "C immediately prior to ovoimplantation. During post-implantation gestation, the body temperature of this female rose steadily, but had reached only 34.6 "C at parturition.Photoperiod correlated closely with seasonal changes in body temperatures and activity levels, and is suggested as the primary synchronizer of seasonal activity and body temperature cycles. Other environmental variables, particularly ambient temperature and snow-cover, appeared to act as modulating influences on these cycles.It is postulated that during the winter, when climatic conditions are responsible for a shortage of food and an increase in heat loss, winter lethargy is an adaptation which enables the European badger to maintain energy balance. Reduced activity and confinement within sheltered setts, together with reduced body temperatures, enable the badgers to rely heavily on energy stored in adipose tissue during the autumn.

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Environmental control of seasonal breeding: a common final mechanism governing seasonal breeding and sexual maturation

Cited by 13 publications

References 92 publications

A note on the concentrations of plasma oestradiol-17β and progesterone around the time of puberty in heifers

A note on the concentrations of plasma oestradiol-17β and progesterone around the time of puberty in heifers

Differential effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour in rams

Overwintering strategies of the badger, Meles meles, at 57 °N

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