The introduction of rams induces an increase in pulsatile LH secretion in cyclic ewes during the breeding season

Hawken, Penny; Beard, A.P.; Esmaili, T.; Kadokawa, Hiroya; Evans, A.C.O.; Blache, Dominique; Martin, Graeme B.

doi:10.1016/j.theriogenology.2007.03.023

Cited by 56 publications

(25 citation statements)

References 31 publications

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“…In the present study the interval between luteolysis and the onset of estrus was not modified by exposure to the male, therefore, the hypothesis that proestrus could be shortened by the presence of males (Ungerfeld and Rubianes 1999;Evans et al 2004;Hawken et al 2007) is not supported by our results. Zarco et al (1988) found that the timing of events after the onset of luteolysis is remarkably constant in sheep, and not related to the duration of the estrous cycle, making alterations in the duration of proestrus an unlikely cause of differences in the estrous cycle length.…”

Section: Discussioncontrasting

confidence: 92%

“…Chemineau (1983), working with goats, found that the distribution of estrus during the eight days that followed the introduction of males was significantly different from the expected uniform distribution, suggesting a possible luteolytic effect of exposure to males. Hawken et al (2007) also suggested that a luteolytic effect of exposure to males could account for the advanced presentation of estrus found after such an exposure. However, in the present study shortening of the estrous cycle consistent with the luteolytic effect of the presence of rams was not observed.…”

Section: Discussionmentioning

confidence: 99%

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Effect of stage of the estrous cycle at the time of initial exposure to rams on the ovarian activity of Pelibuey ewes

Jarquin¹,

Roldán²,

Zarco³

et al. 2014

CZECH J ANIM SCI

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Forty non-lactating, cyclic adult Pelibuey ewes were randomly divided into six groups. Estrus was synchronized within each group using intravaginal sponges and prostaglandin F2α injection at the time of the sponge removal. The sponges were inserted and removed on different dates in each group, but all the groups except the control one were first exposed to rams on the same date (July 17 th ), so that at the time of the first exposure the ewes were either on day 0 (group D0; n = 7), 3 (group D3; n = 7), 8 (group D8; n = 7), 12 (group D12; n = 7) or 14 (group D14; n = 7) of their synchronized estrous cycle. Thereafter the ewes of these groups remained continuously exposed to the males until all the females showed estrus. The ewes in the control group (CG; n = 5) remained isolated from all the males, except for 5-minute periods at the time of estrus detection, which was carried out three times a day. Progesterone concentrations were determined in plasma samples taken daily from two days before the initial exposure to the males until the onset of the next estrus. There were no differences in estrous cycle length between the groups exposed to rams and the control group (P > 0.05). The interval from the assumed onset of the estrous cycle (48 h after sponge removal) until the occurrence of luteolysis was not different between the control group and any of the groups exposed to the males. The interval from luteolysis to estrus was not modified by exposure to the males (P > 0.05). Estrus duration was shorter (P < 0.06) in the control group than in group D3. It is concluded that the exposure of cyclic Pelibuey ewes to males does not advance the time of luteolysis and does not affect the length of the estrous cycle. Therefore, the male effect does not synchronize the next estrus of cyclic Pelibuey ewes.

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Section: Discussioncontrasting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Effect of stage of the estrous cycle at the time of initial exposure to rams on the ovarian activity of Pelibuey ewes

Jarquin¹,

Roldán²,

Zarco³

et al. 2014

CZECH J ANIM SCI

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“…The early occurrence of estrus could be explained by ewes with cycling activity before male introduction. In cyclic ewes, exposition to a ram can advance the LH surge [13], shorten the follicular phase [14], and even cause early luteolysis, but no ovulation can be induced [15]. However, the high estrous activity around Day 10 after joining indicates that ovulation did occur in most ewes immediately after exposure to the rams and that the following luteal phase was shortened.…”

Section: Discussionmentioning

confidence: 99%

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

et al. 2015

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This study compared the reproductive performance of Lacaune dairy ewes exposed to a light program and subsequent male introduction without (n = 36) or with (n = 36) an additional 6-day progestagen treatment during the nonbreeding season. All ewes were exposed to extended day length (16 hours light and 8 hours darkness) for 77 days during winter (December 15 until March 2) followed by increasing natural photoperiod. At the end of the photoperiodic treatment, three blood samples were collected 6 days apart for progesterone (P4) analysis to determine cyclic activity. One half of the ewes were additionally subjected to a 6-day progestagen treatment in combination with PGF2 and eCG at insert withdrawal. Rams fitted with marking harnesses were introduced to females for 45 days and marked ewes recorded. Ewes exposed to the light program only were joined 40 days after the end of photoperiodic treatment, and ewes with additional progestagen treatment were joined 1 day after insert removal (40-44 days after the end of photostimulation). Lambing data were recorded and fertility (percentage of ewes lambing, lambing rate, and litter size) assessed to the first service period and overall. Mean serum P4 concentrations were similarly (P > 0.05) low in both groups (0.4-0.7 ng/mL vs. 0.4-0.6 ng/mL). On the basis of elevated P4 levels (>1 ng/mL), evidence of luteal activity was found in 27.8% of the ewes at the end of the light program. Estrus response was equally high (97.2%) and estrus distribution highly synchronized in progestagen-treated ewes (91.7% within 4 days). In ewes exposed to the light program only, estrous activity was recorded within 4 days (six ewes), from Day 8 to Day 17 (17 ewes) and from Day 19 to Day 25 (12 ewes) after joining. The percentage of ewes that lambed to the first service period was higher (P < 0.05) in ewes exposed to the light program only than that in the group additionally treated with progestagen/PGF2 /eCG (94.4% vs. 69.4%). Overall, the percentage of lambing ewes was similar in both groups (97.2% and 94.4%), and lambing rates (1.4-1.9) and litter sizes (1.9-2.1) were high and not influenced (P > 0.05) by the treatment. In conclusion, this study reports that exposition of Lacaune ewes to artificial long days followed by natural day length and male introduction is highly effective to induce fertile estrous activity during the nonbreeding season and offers a reliable and practical alternative to hormonal manipulation for out-of-season breeding in sheep. a b s t r a c tThis study compared the reproductive performance of Lacaune dairy ewes exposed to a light program and subsequent male introduction without (n ¼ 36) or with (n ¼ 36) an additional 6-day progestagen treatment during the nonbreeding season. All ewes were exposed to extended day length (16 hours light and 8 hours darkness) for 77 days during winter (December 15 until March 2) followed by increasing natural photoperiod. At the end of the photoperiodic treatment, three blood samples were collected 6 days apart for progesterone (...

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“…generate corresponding LH pulses, and so the that basal LH levels are diminished [20]. Therefore, it is assumed that the refractory mechanism may also be necessary to limit the bursting frequency and to generate appropriate LH pulses when the female is continuously exposed to the male in nature [1,3,4,34].…”

Section: Discussionmentioning

confidence: 99%

Effects of Brief Exposure of Male Pheromone on Multiple-Unit Activity at Close Proximity to Kisspeptin Neurons in the Goat Arcuate Nucleus

Murata

Wakabayashi

Sakamoto

et al. 2011

Journal of Reproduction and Development

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Abstract. Exposure of females to the male pheromone induces pulsatile release of gonadotropin-releasing hormone (GnRH) in goats. Recently, kisspeptin neurons in the arcuate nucleus (ARC) have been suggested to represent the proximate source of the GnRH pulse generator. In this study, we examined the effects of the pheromone on multipleunit activity (MUA) in female goats fitted with recording electrodes aimed at the ARC kisspeptin neurons. In all eight goats, periodic bursts in MUA (MUA volleys), which were considered to be electrophysiological manifestations of the GnRH pulse generator, were observed. The mean intervolley interval (T) during the control period was calculated in each goat that was then exposed to the male pheromone for 1 sec at timings of 1/4 T, 1/2 T or 3/4 T after one regularly occurring MUA volley. An instantaneous rise in MUA was observed immediately after the exposure regardless of timing. Exposure at a timing of 3/4 T resulted in an MUA volley within 60 sec following the instantaneous rise in all goats. In contrast, an MUA volley was induced in only 2 goats by exposure at 1/2 T, while exposure at 1/4 T failed to induce an MUA volley in any goats. These results suggest that transmission of the pheromone signal to the ARC, represented by an instantaneous rise, activates the GnRH pulse generator. Moreover, the timing-dependent pheromone action in inducing an MUA volley indicates that the GnRH pulse generator has a refractory period for the pheromone signal after the burst. Key words: GnRH pulse generator, Goat, Kisspeptin, Male effect, Pheromone (J. Reprod. Dev. 57 : 197-202, 2011) n goats and sheep, exposure of seasonally anestrous females to the primer pheromone secreted by sexually mature males results in an out-of-seasonal ovulation [1][2][3][4]. Since the initial endocrine event following reception of the pheromone is the stimulation of pulsatile luteinizing hormone (LH) secretion, it has been thought that the central target of the pheromone signal is the GnRH pulse generator [1,[3][4][5], i.e., the neural substrate that generates intermittent GnRH discharges into the portal vessels, thereby regulating pulsatile LH secretion into the peripheral circulation [6,7].Although the neural identity of the GnRH pulse generator per se was unclear, it was possible to measure its activity by recording multiple-unit activity (MUA) at the mediobasal hypothalamus. It has been demonstrated that electrophysiological manifestations of the GnRH pulse generator are represented as characteristic increases in MUA (MUA volleys) that are exclusively associated with LH pulses in the monkey [8], rat [9] and goat [10,11]. It might be that observed MUA volleys reflect the pulsatile activation of GnRH nerve terminals as they traverse en passant to the ME. Using this technique, Hamada et al. [12] showed that exposure of the female goat to male hair used as a pheromone source promptly induced an MUA volley, demonstrating for the first time that the pheromone action is in fact intimately associated with the GnRH pul...

show abstract

The introduction of rams induces an increase in pulsatile LH secretion in cyclic ewes during the breeding season

Cited by 56 publications

References 31 publications

Effect of stage of the estrous cycle at the time of initial exposure to rams on the ovarian activity of Pelibuey ewes

Effect of stage of the estrous cycle at the time of initial exposure to rams on the ovarian activity of Pelibuey ewes

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

Effects of Brief Exposure of Male Pheromone on Multiple-Unit Activity at Close Proximity to Kisspeptin Neurons in the Goat Arcuate Nucleus

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