The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Claude Fabre-nys - One of the best experts on this subject based on the ideXlab platform.
-
The "Ram Effect": a model to understand the role of kisspeptin as a relay between socio-sexual interactions and the gonadotropic axis
2017Co-Authors: Claude Fabre-nys, Laurence Dufourny, Rex J. ScaramuzziAbstract:The "Ram Effect": a model to understand the role of kisspeptin as a relay between socio-sexual interactions and the gonadotropic axis. 47. European Brain and Behaviour Society Meeting
-
Influence of stress and sexual experience in the response to the Ram Effect
2016Co-Authors: Nathalie Debus, Gilles Viudes, Francois Bocquier, Claude Fabre-nysAbstract:Influence of stress and sexual experience in the response to the Ram Effect. 18. International Congress on Animal Reproduction (ICAR)
-
The "Ram Effect": A "non-classical" mechanism for inducing LH surges in sheep
PLoS ONE, 2016Co-Authors: Claude Fabre-nys, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Stéphanie Martinet, Rex J. ScaramuzziAbstract:During spring sheep do not normally ovulate but exposure to a Ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a Ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the “Ram Effect” in ewes that had a “precocious” LH surge (starting within 6 hours), a “normal” surge (between 6 and 28h) and “late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of Ram introduction among ewes with the three types of LH surge. “Precocious” LH surges were not preceded by a large increase in E2 unlike “normal” surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the “precocious” LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the “Ram Effect”. Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a Ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to Ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active Ram. Collectively these results suggest that in anoestrous ewes NA is involved in Ram-induced LH secretion as observed in other induced ovulators.
-
The "Ram Effect": new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions
Frontiers in Neuroscience, 2015Co-Authors: Claude Fabre-nys, Keith M. Kendrick, Rex J. ScaramuzziAbstract:Reproduction in mammals is controlled by the hypothalamo-pituitary-gonadal (HPG) axis under the influence of external and internal factors such as photoperiod, stress, nutrition, and social interactions. Sheep are seasonal breeders and stop mating when day length is increasing (anestrus). However, interactions with a sexually active Ram during this period can override the steroid negative feedback responsible for the anoestrus state, stimulate luteinizing hormone (LH) secretion and eventually reinstate cyclicity. This is known as the "Ram Effect" and research into the mechanisms underlying it is shedding new light on HPG axis regulation. The first step in the Ram Effect is increased LH pulsatile secretion in anestrus ewes exposed to a sexually active male or only to its fleece, the latter finding indicating a "pheromone-like" Effect. Estradiol secretion increases in all ewes and this eventually induces a LH surge and ovulation, just as during the breeding season. An exception is a minority of ewes that exhibit a precocious LH surge (within 4 h) with no prior increase in estradiol. The main olfactory system and the cortical nucleus of the amygdala are critical brain structures in mediating the Ram Effect since it is blocked by their inactivation. Sexual experience is also important since activation (increased c-fos expression) in these and other regions is greatly reduced in sexually naïve ewes. In adult ewes kisspeptin neurons in both arcuate and preoptic regions and some preoptic GnRH neurons are activated 2 h after exposure to a Ram. Exposure to Rams also activates noradrenergic neurons in the locus coeruleus and A1 nucleus and increased noradrenalin release occurs in the posterior preoptic area. Pharmacological modulation of this system modifies LH secretion in response to the male or his odor. Together these results show that the Ram Effect can be a fruitful model to promote both a better understanding of the neural and hormonal regulation of the HPG axis in general and also the specific mechanisms by which male cues can overcome negative steroid feedback and trigger LH release and ovulatory cycles.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect
Reproduction, 2015Co-Authors: Claude Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the 'Ram Effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'Ram Effect' following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2-4 h after Rams were introduced and remained elevated for 14.5±0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the 'Ram Effect' and insensitivity of the hypothalamus to the E2-positive feedback signal.
Rex J. Scaramuzzi - One of the best experts on this subject based on the ideXlab platform.
-
The "Ram Effect": a model to understand the role of kisspeptin as a relay between socio-sexual interactions and the gonadotropic axis
2017Co-Authors: Claude Fabre-nys, Laurence Dufourny, Rex J. ScaramuzziAbstract:The "Ram Effect": a model to understand the role of kisspeptin as a relay between socio-sexual interactions and the gonadotropic axis. 47. European Brain and Behaviour Society Meeting
-
The "Ram Effect": A "non-classical" mechanism for inducing LH surges in sheep
PLoS ONE, 2016Co-Authors: Claude Fabre-nys, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Stéphanie Martinet, Rex J. ScaramuzziAbstract:During spring sheep do not normally ovulate but exposure to a Ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a Ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the “Ram Effect” in ewes that had a “precocious” LH surge (starting within 6 hours), a “normal” surge (between 6 and 28h) and “late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of Ram introduction among ewes with the three types of LH surge. “Precocious” LH surges were not preceded by a large increase in E2 unlike “normal” surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the “precocious” LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the “Ram Effect”. Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a Ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to Ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active Ram. Collectively these results suggest that in anoestrous ewes NA is involved in Ram-induced LH secretion as observed in other induced ovulators.
-
The "Ram Effect": new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions
Frontiers in Neuroscience, 2015Co-Authors: Claude Fabre-nys, Keith M. Kendrick, Rex J. ScaramuzziAbstract:Reproduction in mammals is controlled by the hypothalamo-pituitary-gonadal (HPG) axis under the influence of external and internal factors such as photoperiod, stress, nutrition, and social interactions. Sheep are seasonal breeders and stop mating when day length is increasing (anestrus). However, interactions with a sexually active Ram during this period can override the steroid negative feedback responsible for the anoestrus state, stimulate luteinizing hormone (LH) secretion and eventually reinstate cyclicity. This is known as the "Ram Effect" and research into the mechanisms underlying it is shedding new light on HPG axis regulation. The first step in the Ram Effect is increased LH pulsatile secretion in anestrus ewes exposed to a sexually active male or only to its fleece, the latter finding indicating a "pheromone-like" Effect. Estradiol secretion increases in all ewes and this eventually induces a LH surge and ovulation, just as during the breeding season. An exception is a minority of ewes that exhibit a precocious LH surge (within 4 h) with no prior increase in estradiol. The main olfactory system and the cortical nucleus of the amygdala are critical brain structures in mediating the Ram Effect since it is blocked by their inactivation. Sexual experience is also important since activation (increased c-fos expression) in these and other regions is greatly reduced in sexually naïve ewes. In adult ewes kisspeptin neurons in both arcuate and preoptic regions and some preoptic GnRH neurons are activated 2 h after exposure to a Ram. Exposure to Rams also activates noradrenergic neurons in the locus coeruleus and A1 nucleus and increased noradrenalin release occurs in the posterior preoptic area. Pharmacological modulation of this system modifies LH secretion in response to the male or his odor. Together these results show that the Ram Effect can be a fruitful model to promote both a better understanding of the neural and hormonal regulation of the HPG axis in general and also the specific mechanisms by which male cues can overcome negative steroid feedback and trigger LH release and ovulatory cycles.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect
Reproduction, 2015Co-Authors: Claude Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the 'Ram Effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'Ram Effect' following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2-4 h after Rams were introduced and remained elevated for 14.5±0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the 'Ram Effect' and insensitivity of the hypothalamus to the E2-positive feedback signal.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect.
Reproduction (Cambridge England), 2015Co-Authors: C. Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the ‘Ram Effect’ and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the ‘Ram Effect’ following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2–4 h after Rams were introduced and remained elevated for 14.5G0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the ‘Ram Effect’ and insensitivity of the hypothalamus to the E2-positive feedback signal. Free French abstract: A French translation of this abstract is freely available at http://www.reproduction-online.org/content/149/5/511/ suppl/DC1. Reproduction (2015) 149 511–521
Rodolfo Ungerfeld - One of the best experts on this subject based on the ideXlab platform.
-
Reproductive response of mature and nulliparous yearling ewes to the Ram Effect during the non-breeding season
Small Ruminant Research, 2016Co-Authors: Rodolfo UngerfeldAbstract:Abstract Sudden introduction of Rams to ewes that remained isolated from males during the non-breeding season induces ovulation and thus out-of-season breeding. The aim of this study was to compare the reproductive response of mature and nulliparous yearling ewes to the Ram Effect during the non-breeding season. The experiment was performed during October–November (mid non-breeding season) with 122 Merilin ewes 56 were mature multiparous (group ME) and 66 nulliparous, 1 year old ewe lambs (group HE) that previously remained isolated from males. All ewes were pretreated with intravaginal sponges for 6 days before the introduction of the Rams. More ME than HE ewes ovulated (87.5 vs 66.7%, P
-
Equine chorionic gonadotrophin administration to Rams improves their Effectiveness to stimulate anoestrous ewes (the "Ram Effect").
Animal reproduction science, 2014Co-Authors: Rodolfo Ungerfeld, Neftali Clemente, Lorena Bonjour, Agustin OrihuelaAbstract:Ewes' response to Ram Effect is related to the strength of androgen-dependent Ram signals. Experiment 1 aimed to determine if the administration of a single dose of 1000IU of eCG to Rams three days before joining them with ewes enhance their ability to stimulate females. Based on the results of Experiment 1, in a second experiment Rams received two doses seven and three days before their introduction to females. In Experiment 1, Rams treated or not with eCG were joined with ewes, and estrous was recorded until Day 5 (Day 0=Rams and ewes were joined), and from Day 15 to Day 23. In addition, serum testosterone concentration was measured in all Rams in the first recorded period. Testosterone values were greater in eCG-E1 than in Con-E1 Rams on Days 0 and 2. The percentage of ewes in estrus was similar in both groups. In Experiment 2, Rams were treated with two doses of eCG on Days -7 and -3 or remained as untreated controls. Estrous was recorded until Day 5, and pregnancy rate on Day 46; testosterone was measured in samples collected from all Rams. Testosterone concentration was greater in eCG-E2 than Con-E2 Rams from Day -5 to Day 1, and tended to do so on Day 2. More eCG-E2 than Con-E2 ewes came into estrus and became pregnant. It was concluded that treatment of Rams with two high doses of eCG before joining them with anestrous ewes, enhanced their ability to induce ewes' cyclic activity (the "Ram Effect").
-
Does introduction of Rams during the late luteal phase promote the estrus response in cyclic ewes
Small Ruminant Research, 2014Co-Authors: J. Meilán, Rodolfo UngerfeldAbstract:Abstract The administration of two doses of PGF2α is widely used for estrous synchronization in cyclic ewes. The introduction of Rams to previously isolated ewes (Ram Effect) induces an increase in LH pulsatility which stimulates estradiol secretion. Consequently, the introduction of the Rams may trigger the luteolytic process through the increase of estradiol. Therefore, the aim of our first experiment was to determine if the second dose of a two PGF2α treatment can be substituted by half PGF2α dose plus the Ram Effect. Ewes were randomly assigned to 3 experimental groups. Ewes from 2 of those groups (E1-PGFD: n = 91, and PGHD: n = 110) remained in permanent contact with 16 vasectomized males since Day-40 (Day 0 = introduction of the Rams). Both groups received a dose of PGF2α on Day-13. On Day 0, E1-PGFD ewes received a second dose of PGF2α, and PGHD ewes received a half-dose. Ewes from the third group (HD + RE; n = 95) remained isolated from males until Day 0, and received a dose of PGF2α on Day-13, and a half-dose on Day 0. On Day 0, the three groups were joined. The introduction of the Rams increased the number of ewes that came into estrus early after the second dose, but this difference was not maintained the following days. Thus, we designed another experiment to determine if the day of the late luteal phase in which ewes are stimulated by the Rams (12–15 days after a dose of PGF2α dose) influences the response. The ewes were randomly assigned to five groups, from which only the control group ( n = 44) remained in contact with males; the other 174 ewes remained isolated from males since Day-30. Estrous cycles were presynchronized with 2 PGF2α doses separated 7 days, and received a third dose 13 days later (Day 0) (control group), or a half-dose plus the introduction of Rams 12, 13, 14 or 15 days later (Day 0). However, we did not observe any differences in the estrus response according to the estrous cycle day. In conclusion, the Ram Effect was Effective substituting half PGF2α in part of the flock, but the response was unrelated to the day of the late luteal phase in which the ewes are stimulated.
-
Response of ewes primed with new CIDRs, previously used CIDRs, or previously used and autoclaved CIDRs to the Ram Effect during the non-breeding season
Animal reproduction, 2013Co-Authors: Rodolfo Ungerfeld, D. Gamboa, L. Álvarez, Mexico CityAbstract:The ovulation induced in anestrous ewes by the sudden introduction of males is not accompanied by estrous behavior unless ewes are primed with progestagens. Although CIDR devices (which contain 0.3 g of progesterone; Pfizer, Auckland, New Zealand) may be used for more than one treatment, conception rates decrease when CIDRs previously used for long times are used again. In cows, if previously used CIDRs are autoclaved, the initial rises in plasma progesterone concentrations are not different to those obtained with a new CIDR. Our objective was to compare the estrous and pregnancy rates of ewes induced to ovulate with the Ram Effect during the non-breeding season to ewes primed with a new CIDR, a previously used CIDR, or a previously used autoclaved CIDR. Ninety-two ewes were randomly allocated to three groups and received a new CIDR (group NC, n = 30), a previously used CIDR (UC, n = 30), or a used-autoclaved CIDR (UAC, n = 32) for 8 days. Used CIDRs were used for 22 days; the CIDRs used in UAC ewes were previously autoclaved. At CIDR withdrawal ewes were joined with adult Rams and 20 additional ewes with induced estrous (1 Ram:13 ewes). Marked ewes were detected every 24 h for 4 days. Forty days after estrus, pregnancy was determined by transrectal ultrasound. Blood samples were collected from 8 ewes from each group 5 and 6 days after CIDR insertion, and at the moment of CIDR withdrawal, and progesterone was measured by radioimmunoassay. Estrous and pregnancy rates were greater in NC than in UC and UAC ewes (estrous: 56.7 vs. 26.7 and 15.6%; pregnancy rate: 50.0 vs. 13.3 and 15.6% for NC, UC, and UAC ewes, respectively; P < 0.05). Progesterone concentration was greater (P < 0.001) in NC than in UC and UAC ewes. No difference was found between UC and UAC groups for any paRameter. Overall, we concluded that autoclaving the CIDRs previously used for 22 days had no positive Effects on estrous and pregnancy rates when applied as primings for the Ram Effect during the non-breeding season. This may be explained by the fact that progesterone concentrations in UC and UAC ewes were below luteal levels during the last days of the treatment.
-
Seasonal reproductive patterns and Effectiveness as teasers (Ram Effect) of Corriedale and Milchschaf Rams
Animal Production Science, 2012Co-Authors: Rodolfo UngerfeldAbstract:The first objective of this study was to compare the seasonal reproductive pattern of Corriedale and Milchschaf Rams. Because seasonal patterns were similar, a second objective was to compare the Effectiveness of Rams from both breeds to induce oestrus in seasonally anoestrous Corriedale ewes using the Ram Effect. In the first experiment, the seasonal changes of bodyweight, scrotal circumference, testosterone concentrations, sexual behaviour towards oestrous ewes (ano-genital sniffing, lateral approaches, flehmen, mount attempts, mounts, and copulation), and semen characteristics (total spermatozoa in the ejaculate, mass motility, and percentage of alive and normal spermatozoa) were recorded during 13 months in five Corriedale and seven Milchschaf Rams. All recorded variables changed through the year, with maximum reproductive patterns occurring in summer and autumn. Milchschaf Rams were heavier than Corriedale Rams, but no difference was observed in their reproductive patterns. Experiment 2 was performed during the non-breeding season with 169 Corriedale and Polwarth mulitparous ewes. All ewes were isolated from the Rams so that they could not see, hear or smell them (minimum distance: 1000 m) from Day –40. They were primed over 8 days with an intravaginal sponge impregnated with 50 mg of medroxiprogesterone. Four Corriedale Rams were introduced to 83 ewes, and four Milchschaf Rams to the remaining 86 ewes at sponge withdrawal, and oestrus was recorded for 5 days. On Day 5, no ewe of the group bred with Milchschaf Rams was marked. By contrast, 46 out of 83 (55.4%) of the ewes bred with Corriedale Rams were marked (P < 0.0001). It was concluded that reproductive seasonal pattern of Corriedale and Milchschaf Rams, including scrotal circumference, testosterone concentrations, sexual behaviour and semen characteristics, was similar. However, Corriedale Rams were more Effective than Milchschaf Rams in inducing oestrus in anoestrus ewes (the Ram Effect).
Audrey Chanvallon - One of the best experts on this subject based on the ideXlab platform.
-
The "Ram Effect": A "non-classical" mechanism for inducing LH surges in sheep
PLoS ONE, 2016Co-Authors: Claude Fabre-nys, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Stéphanie Martinet, Rex J. ScaramuzziAbstract:During spring sheep do not normally ovulate but exposure to a Ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a Ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the “Ram Effect” in ewes that had a “precocious” LH surge (starting within 6 hours), a “normal” surge (between 6 and 28h) and “late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of Ram introduction among ewes with the three types of LH surge. “Precocious” LH surges were not preceded by a large increase in E2 unlike “normal” surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the “precocious” LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the “Ram Effect”. Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a Ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to Ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active Ram. Collectively these results suggest that in anoestrous ewes NA is involved in Ram-induced LH secretion as observed in other induced ovulators.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect
Reproduction, 2015Co-Authors: Claude Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the 'Ram Effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'Ram Effect' following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2-4 h after Rams were introduced and remained elevated for 14.5±0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the 'Ram Effect' and insensitivity of the hypothalamus to the E2-positive feedback signal.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect.
Reproduction (Cambridge England), 2015Co-Authors: C. Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the ‘Ram Effect’ and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the ‘Ram Effect’ following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2–4 h after Rams were introduced and remained elevated for 14.5G0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the ‘Ram Effect’ and insensitivity of the hypothalamus to the E2-positive feedback signal. Free French abstract: A French translation of this abstract is freely available at http://www.reproduction-online.org/content/149/5/511/ suppl/DC1. Reproduction (2015) 149 511–521
-
The Effect of short-term nutritional supplementation and body condition on the pituitary and ovarian responses of anoestrus ewes to the "Ram Effect
Journal of Veterinary Science and Technology, 2011Co-Authors: Lisa Johnson, Claude Fabre-nys, Audrey Chanvallon, Lionel Lardic, Dominique François, Thierry Fassier, Jean-baptiste Menassol, Hannah Mary Brown, Rex J. ScaramuzziAbstract:In sheep production, the “Ram Effect” is a technique for inducing fertility in seasonal anoestrus and “flushing” a technique to increase litter size. Often used individually, we wanted to know if they could be used together to improve reproductive performance of ewes bred during the anoestrous season. Two experiments were conducted; the first with Île-de-France ewes (N=30) comprised a control and a group fed a nutritional supplement and the second with Romane ewes (N=60) replicated these treatments at two levels of body condition. The ewes were stimulated with the “Ram Effect” and the following responses measured (i) blood concentrations of LH, FSH, oestradiol, progesterone, glucose and insulin (ii) oestrus and (iii) ovarian cyclicity. Supplementation increased blood glucose and insulin in experiment 1 but not in experiment 2 but it had no Effect on FSH; it reduced oestradiol in xperiment 2 but not in experiment 1. Higher body condition was associated with higher blood glucose and insulin but not FSH or oestradiol. In addition, higher body condition was associated with a greater proportion of ewes responding to the “Ram Effect” and greater short-term responses for LH and oestradiol; supplementation had no Effect on these responses. In experiment 1 but not experiment 2, supplementation was associated with a higher proportion of ewes in oestrus. The results demonstrate that there are close relationships among the oncentrations of LH and estradiol, the LH surge and the ovarian cyclicity in response to the “Ram Effect”. These data show an Effect of ody condition on “Ram Effect” that can modify cyclicity and suggest an Effect of short-term nutritional upplementation on oestrus. Furthermore these data also suggest that the functional capacity of follicles at the time of the Ram Effect” is an important determinant of outcome.
-
New insights into the influence of breed and time of the year on the response of ewes to the 'Ram Effect'.
Animal : an international journal of animal bioscience, 2011Co-Authors: Audrey Chanvallon, Nathalie Debus, Rex J. Scaramuzzi, L. Sagot, E. Pottier, Dominique François, T. Fassier, C. Fabre-nysAbstract:Exposure of anoestrous ewes to Rams induces an increase in LH secretion, eventually leading to ovulation. This technique therefore is an Effective, low-cost and hormone-free way of mating sheep outside the breeding season. However, the use of this technique is limited by the variability of the ewes’ responses. In this study, our objective was to understand more completely the origins of this variability and to determine the relative roles of breed, the point in time during anoestrus and the depth of anoestrus on the response to the ‘Ram Effect’. In the first experiment, the pattern of anoestrus on the basis of the concentration of progesterone determined weekly, was determined in four breeds including two less seasonal (Merinos d'Arles and Romane), one highly seasonal (Mouton Vendeen) and one intermediate (Ile-de-France) breeds. Anoestrus was longer and deeper in Mouton Vendeen and Ile-de-France than in Romane or Merinos d'Arles. In the second experiment, we used the same four breeds and tested their hypophyseal response to a challenge with a single dose of 75 ng gonadotrophin-releasing hormone (GnRH) in early, mid and late anoestrus, and then we examined their endocrine and ovarian responses to the ‘Ram Effect’. Most (97%) ewes responded to GnRH and most (93%) showed a short-term increase in LH pulsatility following the ‘Ram Effect’. The responses in both cases were higher in females that went on to ovulate, suggesting that the magnitude of the hypophyseal response to a GnRH challenge could be a predictor of the response to the ‘Ram Effect’. As previously observed, the best ovarian response was in Merinos d'Arles at the end of anoestrus. However, there was no relationship between the proportion of females in the flock showing spontaneous ovulation and the response to the ‘Ram Effect’ of anoestrous ewes from the same flock.
C. Fabre-nys - One of the best experts on this subject based on the ideXlab platform.
-
The Two Populations of Kisspeptin Neurons Are Involved in the Ram-Induced LH Pulsatile Secretion and LH Surge in Anestrous Ewes.
Endocrinology, 2017Co-Authors: C. Fabre-nys, Didier Lomet, Stéphanie Martinet, Juliette Cognie, Laurence Dufourny, Meriem Ghenim, Olivier Lasserre, Robert P. Millar, Satoshi Ohkura, Yuta SuetomiAbstract:Exposure to a Ram during spring stimulates luteinizing hormone (LH) secretion and can induce ovulation in sexually quiescent ewes ("Ram Effect"). Kisspeptin (Kiss) present in the arcuate nucleus (ARC) and the preoptic area (POA) is a potent stimulators of LH secretion. Our aim was to investigate whether Kiss neurons mediate the increase in LH secretion during the Ram Effect. With double immunofluorescent detection, we identified Kiss neurons (Kiss IR) activated (Fos IR) by exposure to a Ram for 2 hours (M2) or 12 hours (M12) or to ewes for 2 hours (C). The density of cells Kiss + Fos IR and the proportion of Kiss IR cells that were also Fos IR cells were higher in M2 and M12 than in C in ARC (P < 0.002) and POA (P < 0.02). In ARC, these paRameters were also higher in M12 than in M2 (P < 0.02 and P < 0.05). Kiss antagonist (P234 10-6M) administered by retrodialysis in POA for 3 hours at the time of introduction of the Ram reduced the amplitude of the male-induced increase in LH concentration compared with solvent (P < 0.02). In ARC, P234 had a more limited Effect (P < 0.038 1 hour after P234) but pulse frequency increased less than after solvent (P = 0.07). In contrast, Kiss antagonist (P271 10-4M) infused in ARC but not POA 6 to 18 hours after introduction of the Ram prevented the LH surge in the ewe (0/6 vs 4/5 and 4/6 in C). These results suggest that both populations of Kiss neurons are involved in the Ram-induced pulsatile LH secretion and in the LH surge.
-
Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the Ram Effect.
Reproduction (Cambridge England), 2015Co-Authors: C. Fabre-nys, Nathalie Debus, Audrey Chanvallon, Joëlle Dupont, Lionel Lardic, Didier Lomet, Dominique François, Frédéric Bouvier, Christelle Rame, Rex J. ScaramuzziAbstract:The proportion of anoestrous ewes ovulating after exposure to a sexually active Ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the Ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the ‘Ram Effect’ and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the ‘Ram Effect’ following exposure to Rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2–4 h after Rams were introduced and remained elevated for 14.5G0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to Rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these paRameters. These results demonstrate that the LH surge induced by the Rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the ‘Ram Effect’ and insensitivity of the hypothalamus to the E2-positive feedback signal. Free French abstract: A French translation of this abstract is freely available at http://www.reproduction-online.org/content/149/5/511/ suppl/DC1. Reproduction (2015) 149 511–521
-
New insights into the influence of breed and time of the year on the response of ewes to the 'Ram Effect'.
Animal : an international journal of animal bioscience, 2011Co-Authors: Audrey Chanvallon, Nathalie Debus, Rex J. Scaramuzzi, L. Sagot, E. Pottier, Dominique François, T. Fassier, C. Fabre-nysAbstract:Exposure of anoestrous ewes to Rams induces an increase in LH secretion, eventually leading to ovulation. This technique therefore is an Effective, low-cost and hormone-free way of mating sheep outside the breeding season. However, the use of this technique is limited by the variability of the ewes’ responses. In this study, our objective was to understand more completely the origins of this variability and to determine the relative roles of breed, the point in time during anoestrus and the depth of anoestrus on the response to the ‘Ram Effect’. In the first experiment, the pattern of anoestrus on the basis of the concentration of progesterone determined weekly, was determined in four breeds including two less seasonal (Merinos d'Arles and Romane), one highly seasonal (Mouton Vendeen) and one intermediate (Ile-de-France) breeds. Anoestrus was longer and deeper in Mouton Vendeen and Ile-de-France than in Romane or Merinos d'Arles. In the second experiment, we used the same four breeds and tested their hypophyseal response to a challenge with a single dose of 75 ng gonadotrophin-releasing hormone (GnRH) in early, mid and late anoestrus, and then we examined their endocrine and ovarian responses to the ‘Ram Effect’. Most (97%) ewes responded to GnRH and most (93%) showed a short-term increase in LH pulsatility following the ‘Ram Effect’. The responses in both cases were higher in females that went on to ovulate, suggesting that the magnitude of the hypophyseal response to a GnRH challenge could be a predictor of the response to the ‘Ram Effect’. As previously observed, the best ovarian response was in Merinos d'Arles at the end of anoestrus. However, there was no relationship between the proportion of females in the flock showing spontaneous ovulation and the response to the ‘Ram Effect’ of anoestrous ewes from the same flock.
-
Sexual experience and tempeRament affect the response of Merino ewes to the Ram Effect during the anoestrous season.
Animal reproduction science, 2010Co-Authors: Audrey Chanvallon, D Blache, A Chadwick, T Esmaili, P A R Hawken, G B Martin, C Viñoles, C. Fabre-nysAbstract:In seasonally anoestrous ewes of many breeds, the introduction of Rams triggers an increase in gonadotrophin secretion that induces ovulation, a phenomenon known as the 'Ram Effect'. The Ram Effect is a practical method for mating ewes outside the natural breeding season, and also can provide synchronised lambing, but the variability of the response, especially in young animals, reduces its potential for widespread application. The aim of our study was to assess two factors that are thought to contribute to the variability in young ewes: tempeRament and sexual experience. We used anovulatory ewes from a flock that had been genetically selected for 'calm' or 'nervous' tempeRament and compared the endocrine and ovarian responses to the Ram Effect in four groups (each n=15): 'calm' and parous (3-6 years old); 'calm' and nulliparous (2 years old); 'nervous' and parous; and 'nervous' and nulliparous. Parous ewes, independently of their tempeRament, exhibited a faster endocrine response and a higher proportion of females cycling after Ram introduction than nulliparous ewes. 'Nervous' ewes exhibited a higher proportion of females cycling after Ram introduction than calm ewes, but only in the nulliparous group. We conclude that tempeRament exerts little influence on the response to the Ram Effect in sexually experienced ewes, and that females of 'nervous' tempeRament appear to respond better when sexually 'naive'. Both sexual experience and tempeRament need to be taken into consideration when flock management involves the Ram Effect. Finally, some ewes were cyclic at Ram introduction, yet exhibited an increase in LH secretion even in the presence of high concentrations of progesterone. The mechanism by which the inhibitory Effect of progesterone on LH secretion was bypassed needs to be clarified.
-
Early sexual experience and stressful conditions affect the response of young ewes to the male.
Physiology & behavior, 2009Co-Authors: Audrey Chanvallon, Rex J. Scaramuzzi, C. Fabre-nysAbstract:Exposure of anoestrous ewes to Rams induces oestrous cycles (the 'Ram Effect'). This response is poor in young-sexually naive females, possibly because they lack sexual experience and are sensitive to stress. Firstly, we assessed the conditions required for the acquisition of sexual experience. We exposed naive females at 5 or 9 months of age to Rams and subsequently assessed their response at 1 year of age, to the Ram Effect. Unexpectedly, 2 weeks pre-exposure at 5 months and under some conditions at 9 months, inhibited the Ram Effect at 1 year of age, suggesting that early contact with Rams was stressful and had long-term negative Effects on reproduction. Consequently, we assessed the combined Effect of stress and sexual experience on responses to the Ram Effect. At 9 months of age, we pre-exposed naive females using sexually active Rams to achieve 'positive' (voluntary contact) or 'negative' (forced contact) experiences, and assessed responses to the Ram Effect at a year of age. In parallel, we subjected naive females to stressful conditions at the time of the male Effect. During pre-exposure, females with 'negative' contact exhibited more vigilance and stress cues and had higher levels of cortisol than 'positive' contact ewes. Regardless of pre-exposure or stress, the response to the Ram Effect at a year of age was inhibited. These experiments confirm that contact with sexual partners can be stressful to young ewes and highlight the need to consider their emotional state when conditioning them to the presence of Rams and when managing breeding progRams.