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Maria Correa L, Moreno RD, Luis Riveros J. Hypothalamic-pituitary-gonadal axis response to photoperiod changes in female guanacos (Lama guanicoe). Gen Comp Endocrinol 2024; 347:114427. [PMID: 38141858 DOI: 10.1016/j.ygcen.2023.114427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 12/13/2023] [Accepted: 12/13/2023] [Indexed: 12/25/2023]
Abstract
The guanaco, a wild South American camelid, is renowned for its remarkable resilience to extreme conditions. Despite this, little is known about how reproductive hormones in female camelids are influenced during their seasonal breeding period, which occurs during long photoperiod. To explore this, the study investigated the response of the hypothalamic-pituitary-gonadal axis in female guanacos during short days (10L:14D; July) and long days (16L:8D; December) in the Mediterranean ecosystem (33°38'28″S, 70°34'27″W). Blood samples from 14 adult animals were collected, and measurements of melatonin, 17β-estradiol, FSH, and LH concentrations were taken. The results showed that melatonin concentration was lower (P < 0.05) during long days than short days, whereas 17β-estradiol, FSH, and LH concentrations were higher (P < 0.05) during long days compared to short days. Furthermore, the study detected the expression of the melatonin receptor 1A and kisspeptin in the hypothalamus and pituitary, suggesting that the pineal gland of female guanacos is sensitive to seasonal changes in day length. These findings also indicate a seasonal variation in the concentration of reproductive hormones, likely linked to the distinct modulation of the hypothalamic-pituitary-gonadal axis of female guanacos during short and long days.
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Affiliation(s)
- Lina Maria Correa
- Escuela de Medicina Veterinaria, Facultad de Recursos Naturales y Medicina Veterinaria, Universidad Santo Tomás, Carlos Schorr 255, Maule, Talca 3460000, Chile; Centro de Innovación de ovinos para el secano-OVISNOVA, Universidad Santo Tomás, Carlos Schorr 255, Maule, Talca 3460000, Chile; Escuela de postgrado, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago 8940000, Chile.
| | - Ricardo D Moreno
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Marcoleta 49, Santiago 8320000, Chile.
| | - José Luis Riveros
- Escuela de postgrado, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago 8940000, Chile; Departamento de Ciencias Animales, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago 8940000, Chile.
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Correa LM, Moreno RD, Riveros JL. The effect of photoperiod and melatonin on plasma prolactin concentrations in female guanaco (Lama guanicoe) in captivity. Reprod Domest Anim 2020; 56:680-683. [PMID: 32979882 DOI: 10.1111/rda.13829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 09/18/2020] [Indexed: 11/29/2022]
Abstract
The present study examined the effects of different photoperiods and melatonin treatment on plasma prolactin concentrations in guanacos, a South American camelid, in captivity. Fourteen adult female guanacos, not gestating or lactating and isolated from males, were studied. The control group was exposed to natural daylight, during short days (N = 7, 10L:14D) and long days (N = 7, 16L:8D). The treatment group (N = 7, 10L:14D) received melatonin implants every 23 days for 6 weeks during long days. Blood samples were taken at intervals of 1 week for 3 weeks, starting the third week of treatment. Prolactin concentrations were measured using competitive ELISA. Plasma concentrations of prolactin in non-lactating female guanacos have seasonal changes, with a higher concentration (p < .001) in short days (3.50 ± 2.24 ng/ml) than long days (1.10 ± 0.91 ng/ml). Melatonin treatment significantly decreases (p < .05) plasma concentrations of prolactin on the 21st day after the treatment. These findings are the first report of an endogenous circannual rhythm of plasma prolactin concentration and the action of melatonin treatment on prolactin secretion in this wild camelid.
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Affiliation(s)
- Lina Maria Correa
- Escuela de postgrado, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Ricardo D Moreno
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - José Luis Riveros
- Departamento de Ciencias Animales, Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago, Chile
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El Allali K, Sghiri A, Bouâouda H, Achaâban MR, Ouzir M, Bothorel B, El Mzibri M, El Abbadi N, Moutaouakkil A, Tibary A, Pévet P. Effect of Melatonin Implants during the Non-Breeding Season on the Onset of Ovarian Activity and the Plasma Prolactin in Dromedary Camel. Front Vet Sci 2018; 5:44. [PMID: 29594158 PMCID: PMC5858023 DOI: 10.3389/fvets.2018.00044] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 02/22/2018] [Indexed: 12/27/2022] Open
Abstract
To examine a possible control of reproductive seasonality by melatonin, continual-release subcutaneous melatonin implants were inserted 4.5 months before the natural breeding season (October-April) into female camels (Melatonin-treated group). The animals were exposed to an artificial long photoperiod (16L:8D) for 41 days prior to implant placement to facilitate receptivity to the short-day signal that is expected with melatonin implants. The treated and control groups (untreated females) were maintained separately under outdoor natural conditions. Ovarian follicular development was monitored in both groups by transrectal ultrasonography and by plasma estradiol-17β concentrations performed weekly for 8 weeks and then for 14 weeks following implant insertion. Plasma prolactin concentrations were determined at 45 and 15 days before and 0, 14, 28, 56, and 98 days after implant insertion. Plasma melatonin concentration was determined to validate response to the artificial long photoperiod and to verify the pattern of release from the implants. Results showed that the artificial long photoperiod induced a melatonin secretion peak of significantly (P < 0.05) shorter duration (about 2.5 h). Melatonin release from the implants resulted in higher circulating plasma melatonin levels during daytime and nighttime which persisted for more than 12 weeks following implants insertion. Treatment with melatonin implants advanced the onset of follicular growth activity by 3.5 months compared to untreated animals. Plasma estradiol-17β increased gradually from the second week after the beginning of treatment to reach significantly (P < 0.01) higher concentrations (39.2 ± 6.2 to 46.4 ± 4.5 pg/ml) between the third and the fifth week post insertion of melatonin implants. Treatment with melatonin implants also induced a moderate, but significant (P < 0.05) suppressive effect on plasma prolactin concentration on the 28th day. These results demonstrate that photoperiod appears to be involved in dromedary reproductive seasonality. Melatonin implants may be a useful tool to manipulate seasonality and to improve reproductive performance in this species. Administration of subcutaneous melatonin implants during the transition period to the breeding season following an artificial signal of long photoperiod have the potential to advance the breeding season in camels by about 2.5 months.
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Affiliation(s)
- Khalid El Allali
- Comparative Anatomy Unit/URAC49, Department of Biological and Pharmaceutical Veterinary Sciences, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Abdelmalek Sghiri
- Animal Reproduction Unit, Department of Medicine, Surgery and Reproduction, Hassan II Agronomy and Veterinary Institute, Rabat, Morocco
| | - Hanan Bouâouda
- Harvard Medical School and Veterans Administration Healthcare System, Boston, MA, United States
| | - Mohamed Rachid Achaâban
- Comparative Anatomy Unit/URAC49, Department of Biological and Pharmaceutical Veterinary Sciences, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Mounir Ouzir
- Group of Research in Physiology and Physiopathology, Department of Biology, Faculty of Science, University Mohammed V, Rabat, Morocco
| | - Béatrice Bothorel
- Neurobiology of Rhythms UPR 3212 CNRS, Institute for Cellular and Integrative Neurosciences, University of Strasbourg, Strasbourg, France
| | - Mohammed El Mzibri
- Biotechnology and Engineering of Biomolecules Unit, National Center of Energy, Science and Nuclear Techniques, Rabat, Morocco
| | - Najia El Abbadi
- Biotechnology and Engineering of Biomolecules Unit, National Center of Energy, Science and Nuclear Techniques, Rabat, Morocco
| | - Adnane Moutaouakkil
- Biotechnology and Engineering of Biomolecules Unit, National Center of Energy, Science and Nuclear Techniques, Rabat, Morocco
| | - Ahmed Tibary
- Comparative Theriogenology, Department of Veterinary Clinical Science, College of Veterinary Medicine, Centre for Reproductive Biology, Washington State University, Pullman, WA, United States
| | - Paul Pévet
- Neurobiology of Rhythms UPR 3212 CNRS, Institute for Cellular and Integrative Neurosciences, University of Strasbourg, Strasbourg, France
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Williams GL, Thorson JF, Prezotto LD, Velez IC, Cardoso RC, Amstalden M. Reproductive seasonality in the mare: neuroendocrine basis and pharmacologic control. Domest Anim Endocrinol 2012; 43:103-15. [PMID: 22579068 DOI: 10.1016/j.domaniend.2012.04.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Revised: 04/11/2012] [Accepted: 04/11/2012] [Indexed: 11/23/2022]
Abstract
Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular and molecular bases of seasonal rhythms has not been realized in any species, many of their synaptic and humoral signaling pathways have been defined. In the mare, neuroendocrine-related studies have focused primarily on the roles of GnRH and interneuronal signaling pathways that subserve the GnRH system in the regulatory cascade. Recent studies have considered the role of a newly discovered neuropeptide, RF-related peptide 3 that could function to inhibit GnRH secretion or gonadotrope responsiveness. Although results that used native peptide sequences have been negative in the mare and mixed in all mammalian females, new studies that used an RFRP3 antagonist (RF9) in sheep are encouraging. Importantly, despite continuing deficits in some fundamental areas, the knowledge required to control seasonal anovulation pharmacologically has been available for >20 yr. Specifically, the continuous infusion of native GnRH is both reliable and efficient for accelerating reproductive transition and is uniquely applicable to the horse. However, its practical exploitation continues to await the development of a commercially acceptable delivery vehicle.
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Affiliation(s)
- G L Williams
- Animal Reproduction Laboratory, Texas AgriLife Research, Beeville, TX 78102, USA.
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Dholpuria S, Vyas S, Purohit GN, Pathak KML. Sonographic monitoring of early follicle growth induced by melatonin implants in camels and the subsequent fertility. J Ultrasound 2012; 15:135-41. [PMID: 23396356 DOI: 10.1016/j.jus.2012.02.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
The present study examined the effect of melatonin implants on follicle growth in dromedary camels two months ahead of their natural breeding season (December to March). Female camels (n = 6) were treated with melatonin implants at the dose rate of 1 implant per 28 kg body weight sc. Control camels (n = 6) were administered an SC placebo implant of 8 ml vitamin A. Ovarian ultrasonography was performed at weekly interval upto 7 weeks. Camels were mated with virile stud when a follicle (≥10 mm) was visible on either of the ovaries. Blood was collected on day 7, 9, 15, 20, 25 and 30 for assay of plasma progesterone and sonography performed at the same time. Small follicles (2-3 mm) appeared around the periphery of ovaries in 83.3% of camels by day 7 and in 100% camels by day 14. By the end of 7th week an ovulatory size follicle (≥1.0 cm) could be observed in 83.3% of treated camels, and these camels were mated with virile studs. In control group, small follicles appeared at the periphery of ovaries only in 66.6% camels but did not progress in growth except in one camel (16.6%) however, ovulating size (≥10 mm) follicle was not observed in any camel by the end of 7th week. All treated camels ovulated and one treated camel became pregnant while early embryonic death occurred in one camel. Non-pregnant camels of both groups were mated during the breeding season. All camels of treatment group and 33.33% camels of control group became pregnant by the end of breeding season (April 2010). It was concluded that melatonin implants can augment the follicle growth in lactating camels ahead of the breeding season and pregnancy can occur on mating. Fertility of treated camels during the breeding season is improved.
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Affiliation(s)
- S Dholpuria
- Veterinary Hospital Garabdesar, District Bikaner, Rajasthan, India
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Salazar-Ortiz J, Camous S, Briant C, Lardic L, Chesneau D, Guillaume D. Effects of nutritional cues on the duration of the winter anovulatory phase and on associated hormone levels in adult female Welsh pony horses (Equus caballus). Reprod Biol Endocrinol 2011; 9:130. [PMID: 21958120 PMCID: PMC3195710 DOI: 10.1186/1477-7827-9-130] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Accepted: 09/29/2011] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND Mares have an annual reproductive rhythm, with a phase of inactivity in midwinter. The aim of this study was to determine the impact of food restriction on physiological and metabolic hallmarks of this rhythm. METHODS Over three successive years, 3 groups of 10 mares were kept under natural photoperiod. A 'well-fed' group was fed to maintain the mares in good body condition; a 'restricted' group received a diet calculated to keep the mares thin and a 'variable' group was fed during some periods like the 'restricted' group and during some other periods like the 'well-fed' group, with the aim of mimicking the natural seasonal variation of pasture availability, but a few months in advance of this natural rhythm. RESULTS Winter ovarian inactivity always occurred and was long in the restricted group. In contrast, in the 'well-fed' group, 40% of mares showed this inactivity, which was shorter than in the other groups. Re-feeding the 'variable' group in autumn and winter did not advance the first ovulation in spring, compared with the 'restricted' group. Measurements of glucose and insulin concentrations in mares from the 'restricted' group during two 24 h periods of blood sampling, revealed no post-prandial peaks. For GH (Growth hormone), IGF-1 and leptin levels, large differences were found between the 'well-fed' group and the other groups. The glucose, insulin, GH and leptin levels but not melatonin level are highly correlated with the duration of ovulatory activity. CONCLUSIONS The annual rhythm driven by melatonin secretion is only responsible for the timing of the breeding season. The occurrence and length of winter ovarian inactivity is defined by metabolic hormones.
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Affiliation(s)
- Juan Salazar-Ortiz
- INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- Université François Rabelais de Tours, F-37041 Tours, France
- IFCE, F-37380 Nouzilly, France
| | - Sylvaine Camous
- INRA, UMR1198 Biologie du Développement et Reproduction, F-78352 Jouy-en-Josas, France
- ENVA, F-94704 Maisons Alfort, France
| | - Christine Briant
- INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- Université François Rabelais de Tours, F-37041 Tours, France
- IFCE, F-37380 Nouzilly, France
| | - Lionel Lardic
- INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- Université François Rabelais de Tours, F-37041 Tours, France
- IFCE, F-37380 Nouzilly, France
| | - Didier Chesneau
- INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- Université François Rabelais de Tours, F-37041 Tours, France
- IFCE, F-37380 Nouzilly, France
| | - Daniel Guillaume
- INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- CNRS, UMR6175 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France
- Université François Rabelais de Tours, F-37041 Tours, France
- IFCE, F-37380 Nouzilly, France
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McManus CJ, Fitzgerald BP. Effect of daily clenbuterol and exogenous melatonin treatment on body fat, serum leptin and the expression of seasonal anestrus in the mare. Anim Reprod Sci 2003; 76:217-30. [PMID: 12586494 DOI: 10.1016/s0378-4320(02)00246-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A small percentage of mature mares continue to exhibit estrous cyclicity during the non-breeding season which is of interest because of the importance of timing of the breeding season to the equine breeding industry. Previously, it was demonstrated that the continuation of estrous cycles was more likely to occur in mature than young mares. Additionally, an apparent association exists between elevated body fat and increased circulating concentrations of leptin, and the occurrence of estrous cycles during the non-breeding season. Two experiments were conducted to test the hypothesis that pharmacological manipulation of body fat and leptin by administration of the beta(2)-adrenergic receptor agonist clenbuterol, with and without continuous treatment with melatonin, would increase the proportion of mares entering anestrus or advance its timing. In Experiment 1, eight mature mares were administered clenbuterol (3.2 microg/kg) daily from October through January and six mares were untreated. In Experiment 2, eight mares were administered clenbuterol daily from June through December, eight mares were treated with continuous release melatonin implants, and seven mares were treated with both clenbuterol and melatonin. Melatonin treatment was included to confirm previous results that constant treatment with melatonin did not advance the timing of anestrus. In both studies, leptin concentrations (P<0.01, both experiments) and body fat percentage (P<0.01, Experiment 1; P<0.05, Experiment 2) declined in response to daily clenbuterol treatment. Unexpectedly, however, this decrease was attenuated in mares also treated with melatonin (P<0.05). Although treatment with clenbuterol was associated with a decline in body fat and circulating concentrations of leptin, the timing or proportion of mares exhibiting anestrus was not modified (P>0.05). The results demonstrate the manipulation of body condition via pharmacological intervention does not modify the mechanisms controlling seasonal anestrus in the mare.
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Affiliation(s)
- C J McManus
- Department of Veterinary Science, Maxwell Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546-0099, USA
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Abstract
In this review, we have attempted to summarize, based on recent data obtained in our laboratory and elsewhere, our current understanding of the regulatory mechanisms of seasonality and discuss the implications with regard to treatment strategies to advance the onset of cyclic reproductive activity in the early spring.
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Affiliation(s)
- P Nagy
- Department of Physiology of Reproduction in Domestic Mammals, National Institute of Agricultural Research (INRA), Nouzilly, France
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Fitzgerald BP, Davison LA, McManus CJ. Evidence for a seasonal variation in the ability of exogenous melatonin to suppress prolactin secretion in the mare. Domest Anim Endocrinol 2000; 18:395-408. [PMID: 10869858 DOI: 10.1016/s0739-7240(00)00058-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In seasonally breeding species photoperiodic information is thought to be conveyed to the reproductive and prolactin axis via changes in circulating concentrations of melatonin. For some species, a constant melatonin stimulus is perceived as a short day, whereas in others no photoperiodic information is provided. In the mare, a preliminary study demonstrated that constant administration of melatonin did not modify prolactin secretion, suggesting that this treatment regimen failed to provide photoperiodic information. To further investigate this proposal and to investigate an alternative explanation, namely a seasonal variation in response to melatonin, 4 experiments were performed. In experiments 1-3, the effects of constant administration of melatonin on prolactin secretion were investigated. In each study the time of treatment initiation varied beginning before the summer solstice, (May 9; Exp. 1), at the autumnal equinox (Sept. 21; Exp. 2) or the winter solstice (Dec. 21; Exp. 3). In Experiment 4, melatonin was administered as a timed daily injection (5 PM) for 6 months, beginning at the summer solstice (June 21). Constantly elevated physiological concentrations of melatonin (expts. 1-3) and an extended nighttime elevation of melatonin (exp. 4) suppressed prolactin concentrations only during the spring and early summer months (April-August). At other times during the year prolactin concentrations were similar to untreated mares. In the presence of a continuous melatonin implant the circannual rhythm of prolactin secretion was not disturbed. The results suggest that the prolactin axis of the mare is sensitive to an inhibitory melatonin signal during a restricted period of time and that at other times is refractory to this signal.
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Affiliation(s)
- B P Fitzgerald
- Department Veterinary Science, Maxwell Gluck Equine Research Center, University of Kentucky, Lexington, KY 40504-0099, USA.
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Peltier MR, Robinson G, Sharp DC. Effects of melatonin implants in pony mares. 2. Long-term effects. Theriogenology 1998; 49:1125-42. [PMID: 10732051 DOI: 10.1016/s0093-691x(98)00061-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The effects of melatonin implant treatment over a 4 wk period at the summer solstice on the transition into and out of the following anovulatory season were evaluated in ovary-intact and ovariectomized mares. Melatonin implants tended to delay the timing of the final ovulation of the breeding season (P = 0.0797) in the ovary-intact mares. Although the decline in LH secretion associated with the end of the breeding season was parallel between treatments and ovarian statuses, the rate of LH secretion, as expressed by its mathematical accumulation, was lower in ovariectomized, melatonin-treated mares than in ovariectomized, control mares suggesting that melatonin administration advanced the offset of the breeding season in ovariectomized mares (P = 0.0001). The first ovulation of the subsequent breeding season was significantly delayed in the melatonin-treated mares as compared with that of control mares (P = 0.0031). During reproductive recrudescence, the time of the onset of the increase in LH secretion was similar among all 4 groups but the patterns of LH secretion were different for each treatment and ovarian status combination (P = 0.0112). Mares with melatonin implants had a slower rate of increase in LH secretion than control mares (P = 0.0001), and ovariectomized mares had a faster rate of LH increase than intact mares (P = 0.0001). These results suggest that melatonin implants during the summer solstice can alter the annual reproductive rhythm in mares and support the concept that endocrine patterns of reproductive recrudescence are not entirely independent of the ovary.
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Affiliation(s)
- M R Peltier
- Department of Animal Science, University of Florida, Gainesville 32611, USA
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11
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Prolactin concentrations are not suppressed in mares administered constant exogenous melatonin. J Equine Vet Sci 1998. [DOI: 10.1016/s0737-0806(98)80185-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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12
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Koskinen E, Huhtinen M, Katila T. Serum progesterone levels in mares in winter and during transitional periods. Acta Vet Scand 1996. [PMID: 9050273 DOI: 10.1186/bf03548080] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Weekly blood samples were collected for serum progesterone determination from 68 mares during the period from September 1990 to June 1991. A total of 78% (53/68) of the mares became anoestrous: 88% (15/17) of mares with foals and 75% (38/51) of dry mares (p = 0.323). Six mares of the 15 which continued cycling showed persistent corpus luteum for 77 days on average (range 42-106 days). Anoestrus began between September and February, most frequently in December, and ended in January to June, most frequently in March. Mares with foal at foot became anoestrous in 2 separate groups, in September and in December. Anoestrus ended most frequently in February in foaled mares. The mares with foals differed significantly from the other mares both at onset (p = 0.0084) and end (p = 0.0218) of anoestrus. However, the effect of the stable was also significant at onset (p = 0.0386) and end (p = 0.0170) of anoestrus. Since all mares with foals were kept in one stable and dry mares in 4 different stables, the effect of stable and possible differing lighting conditions cannot be separated from the foal effect. The length of anoestrus was on average 101 days for lactating mares and 95 days for dry mares (p = 0.6691). In foaled mares its length was on average 159 days in mares which had entered anoestrus as early as in September-October and 62 days in mares entering anoestrus in December (p = 0.001). The effects of breed and age were not significant in any of the parameters.
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