Seasonal Breeding: Nature's Contraceptive

Lincoln, G. A.; Short, R. V.

doi:10.1016/b978-0-12-571136-4.50007-3

Cited by 363 publications

(350 citation statements)

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“…The testes regressed during long days and became maximally redeveloped during short days. This cycle is similar to that observed in normal rams exposed to this lighting regime (12,15).…”

Section: Testiculur Cyclesupporting

confidence: 71%

“…In this breed of sheep, the rams show a marked seasonal cycle in testicular activity which is regulated by photoperiod (12). The physiological control of the testicular cycle involves changes in the secretion of LH and follicle-stimulating hormone from the anterior pituitary gland, which is dictated by the pulsatile secretion of LHRH from the hypothalamus (13,14).…”

mentioning

confidence: 99%

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Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram

Lincoln

1991

J Neuroendocrinology

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Aspartate and glutamate represent a major class of excitatory amino-acid neurotransmitters in the vertebrate brain, and stimulation of glutaminergic receptors by the specific agonist N-methyl-D,L-aspartate (NMDA) induces luteinizing hormone-releasing hormone (LHRH) and LH secretion. In this study, we used NMDA as a probe to investigate the hypothalamic regulation of LH secretion at different stages of a reproductive cycle in Soay rams induced by exposure to alternating 16-week periods of long and short days. NMDA (20 mg/kg) injected intravenously caused an acute increase in blood plasma concentrations of LH, with a significant increase within 2 to 4 min, and peak levels within 20 min. The magnitude of the response changed markedly during the cycle; it was greatest in the sexually inactive phase under long days (with a linear dose-response over the range 1 to 20 mgikg NMDA) and least in the sexually active phase under short days (only 20 mg/kg NMDA produced a small response). Pituitary responsiveness to a standard dose of LHRH (5.3 ng/kg iv) varied only slightly at the different stages and could not account for the observed changes in the LH response to NMDA. There were the expected changes in the endogenous pattern of LH secretion during the cycle, with high frequency LH pulses occurring during the sexually active phase. There was an inverse relationship between the frequency of LH pulses and the LH response to NMDA. Pretreatment of rams with an LHRH antagonist (36 pg/kg iv; Syntex, RS18286) totally blocked the LH response to both NMDA and LHRH, while in a separate study, treatment with dexamethasone (synthetic glucocorticoid, 133.4 pglkg iv) partially blocked the LH responses. The overall results indicate that NMDA stimulates LHRH secretion in the ram and the response is independent of the activation of the hypothalamo-pituitary-adrenal axis. The variation in the LH response during the reproductive cycle may reflect changes in the releasable stores of LHRH in the median eminence. These appear to be depleted in the sexually active phase, when LHRH is secreted in pulses at high frequency. The variation in the response to NMDA may also reflect changes in release of endogenous excitatory amino-acids, which act via NMDA receptors to form part of the physiological regulation of the reproductive cycle in the ram.The dicarboxylic amino-acids aspartate and glutamate represent a major class of excitatory neurotransmitters in the vertebrate brain ( I ) . These amino-acids have excitatory effects through at least three classes of receptors of which the N-methyl-D,Laspartate (NMDA) receptor class is best characterized, and these receptors are apparently involved in the neural control of reproduction (2). Studies in the rat have shown that the administration of NMDA causes the release of luteinizing hormone (LH) from the anterior pituitary gland by inducing the secretion of LHreleasing hormone (LHRH) from the hypothalamus (3, 4), and there is evidence that both NMDA and non-NMDA excitatory amino-acid receptors are in...

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“…The testes regressed during long days and became maximally redeveloped during short days. This cycle is similar to that observed in normal rams exposed to this lighting regime (12,15).…”

Section: Testiculur Cyclesupporting

confidence: 71%

mentioning

confidence: 99%

Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram

Lincoln

1991

J Neuroendocrinology

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“…These results showed that in male goats from subtropical Mexico, the photoperiod is the major environmental factor that controls the annual breeding season. In the experimental group, the photoperiodic rhythm modified the seasonality of testosterone secretion observed in control animals exposed to natural light variations as reported in Alpine bucks and Soay rams (Lincoln and Short, 1980;Delgadillo and Chemineau, 1992).…”

Section: Male Goatsmentioning

confidence: 57%

Environmental and social cues can be used in combination to develop sustainable breeding techniques for goat reproduction in the subtropics

2011

Animal

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Goat breeds from subtropical latitudes show different annual reproductive cycles. Some of them display large seasonal variations in their annual breeding season, while others display a moderate seasonality or sexual activity all year round. This reproductive seasonality causes seasonality of milk, cheese and meat productions and, as a consequence, induces wide variation in producer incomes. To solve this problem and provide methods allowing producers to breed animals during the anestrous period and stabilize production all year round, it is necessary to have a deep knowledge of their annual sexual activity and to identify the environmental factors controlling the timing of the annual reproductive cycle. Then, it is possible to build on these knowledge sustainable breeding techniques adapted to the environmental, economic and social characteristics of the local breeding system. In this review, I will illustrate this strategy through the example of our experiments in subtropical goats. First, we determined the characteristics of the annual breeding season in both male and female goats. Second, we identified the photoperiod as the major environmental factor controlling the timing of this annual breeding season. Third, we used the photoperiod to stimulate indirectly the sexual behavior of does. Indeed, we used photoperiodic treatments to stimulate the sexual activity of bucks during the non-breeding season. These sexually active male goats were then used to induce and synchronize the estrous behavior and ovulatory activity of anestrous females in confined or grazing conditions by using the 'male effect'. Under subtropical conditions, these results constitute an original manner to control the reproductive activity of local goats using the photoperiod combined with the 'male effect.'

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“…The natural breeding season of male goats and rams raised at temperate latitudes lasts from September to October to February to March (Lincoln and Short, 1980;Delgadillo and Chemineau, 1992). The endocrine and reproductive seasonality is mainly controlled by variations of photoperiod: short days stimulate and long days inhibit the sexual activity Delgadillo et al, 1991;Zarazaga et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Continuous light after a long-day treatment is equivalent to melatonin implants to stimulate testosterone secretion in Alpine male goats

Delgadillo

Vélez

Flores

2016

animal

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In rams, artificial long days followed by continuous light stimulate testosterone secretion during the non-breeding season. The objective of this study was to determine whether artificial long days followed by continuous light could stimulate testosterone secretion in Alpine bucks as well as in those exposed to long days followed by a melatonin treatment. All bucks were kept in shaded open pens. Control males were exposed to natural photoperiod conditions (n=5). Males of the two experimental groups were exposed to 2.5 months of long days from 1 December (n=5 each). On 16 February, one group of males was exposed to 24 h of light per day until 30 June; the other group was exposed to natural variations of photoperiod and received two s.c. melatonin implants. Testicular weight was determined every 2 weeks, and the plasma testosterone concentrations once a week. In the control and the two photoperiodic-treated groups, a treatment×time interaction was detected for testicular weight and plasma testosterone concentrations (P<0.001). In control bucks, testicular weight increased from January and peaked in June, whereas in both photoperiodic-treated groups, this variable increased from January, but peaked in April, when the values were higher than in controls (P<0.05). In the control group, plasma testosterone concentrations remained low from January to June, whereas in both photoperiodic-treated groups, this variable remained low from January to March; thereafter, these levels increased in both photoperiodic-treated groups, and were higher than controls in April and May (P<0.05). We conclude that continuous light after a long-day treatment stimulate testosterone secretion in Alpine male goats during the non-breeding season as well as the long days followed by a melatonin treatment. Therefore, continuous light could replace the implants of melatonin.

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Seasonal Breeding: Nature's Contraceptive

Cited by 363 publications

References 68 publications

Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram

Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram

Environmental and social cues can be used in combination to develop sustainable breeding techniques for goat reproduction in the subtropics

Continuous light after a long-day treatment is equivalent to melatonin implants to stimulate testosterone secretion in Alpine male goats

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