Seasonal serum concentrations of melatonin in cycling and noncycling mares.
Abstract: To determine whether secretory patterns of melatonin change throughout the seasons in mares, blood samples were drawn byvenipuncture from nine mares at noon and midnight for five successive days at monthly intervals from August through July at the University of Missouri in Columbia, MO. In addition, during September, December, March, and June, blood samples were drawn from indwelling catheters at 2-h intervals for 48 or 72 h. Mares were predominantly Quarter Horses weighing approximately 450 kg and ranged from 3 to 12 yr of age. Mares were housed in outdoor paddocks with three-sided run-in sheds for shelter. During the noon and midnight bleeding period, mares were placed in a larger open-sided barn with outside runs. Mares remained outdoors with the barn being used as a shelter in the event of inclement weather. All lights in the shed were converted to red light. Often, moonlight provided enough illumination to collect blood samples. Mares were returned to their normal paddock after each sampling period. For analysis of data, a mare was considered to be cycling if serum concentrations of progesterone were greater than 1 ng/ mL. For a mare to be classified as exhibiting a nocturnal rise of melatonin, serum concentrations of melatonin had to be at least two times greater at midnight than at noon. By month, a relationship did not exist (chi2; P > 0.05) among mares that were exhibiting estrous cycles and exhibiting nocturnal rises of melatonin. Likewise, examination of serum profiles of melatonin taken at 2-h intervals for 48 h revealed considerable variation among mares throughout the seasons. A nocturnal rise in serum melatonin was observed only in June (P < 0.02). In March and December, serum melatonin was greater in cycling mares than noncycling mares, but the elevation was not associated with light-dark periods (P < 0.01). Two of the mares exhibited estrous cycles throughout the seasons but melatonin secretion in these two mares were similar to that observed in the seven mares that demonstrated seasonal anestrous. From these results, it does not appear that changes in serum concentrations of melatonin are used as a cue to regulate cyclic activity in the mare throughout the seasons.
Publication Date: 2002-12-05 PubMed ID: 12462263DOI: 10.2527/2002.80112949xGoogle Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research investigates whether the secretion patterns of melatonin, a hormone impacting sleep and reproduction, change across seasons in mares. It found that these patterns do not seem to regulate cyclical activity in mares throughout the year.
Study Design and Sample
- The study was conducted at the University of Missouri, where blood samples were collected from nine mares of predominantly Quarter Horse breed. Their ages ranged from 3 to 12 years while they weighed around 450 kg.
- The blood samples were taken at noon and midnight for five consecutive days every month from August through July. In addition, exhaustive data was collected in September, December, March, and June by drawing blood every two hours for a period of 48 to 72 hours.
- The mares were kept in outdoor paddocks with a three-sided shed for shelter. During the sampling period, they were moved to a larger barn with outside runs.
- For the analysis, a mare was said to be cycling if its progesterone concentrations exceeded 1 ng/mL. To be classified as having a nocturnal rise in melatonin, the hormone concentration needed to be at least twice as high at midnight than at noon.
Findings
- The results showed no consistent relationship throughout the year between mares that were cycling and those that exhibited a nocturnal rise in melatonin.
- Across seasons, there was considerable variability in the melatonin profiles of mares, with a noticeable nocturnal rise in melatonin serum only observed in June.
- In March and December, though melatonin levels were higher in cycling mares than noncycling ones, this increase was not related to the day-night cycle.
- Interestingly, two mares cycled all year round, but their melatonin secretion patterns resembled those of the other seven mares that displayed seasonal anestrus – a period of sexual inactivity most prevalent in animals.
Conclusion
- Contrary to the initial hypothesis, the study found that changes in melatonin concentration do not seem to serve as an indicator for regulating cyclical activity in horses across the year.
- This conclusion, based on detailed analysis of melatonin profiles over time and during different cycles of the reproductive stage, suggests that melatonin might have a different role in horses than previously thought.
Cite This Article
APA
Diekman MA, Braun W, Peter D, Cook D.
(2002).
Seasonal serum concentrations of melatonin in cycling and noncycling mares.
J Anim Sci, 80(11), 2949-2952.
https://doi.org/10.2527/2002.80112949x Publication
Researcher Affiliations
- Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-1151, USA. mdiekman@purdue.edu
MeSH Terms
- Anestrus / blood
- Animals
- Circadian Rhythm
- Estrus / blood
- Female
- Horses / blood
- Horses / physiology
- Melatonin / blood
- Melatonin / metabolism
- Photoperiod
- Progesterone / blood
- Seasons
Citations
This article has been cited 3 times.- Contreras-Correa ZE, Messman RD, Swanson RM, Lemley CO. Melatonin in Health and Disease: A Perspective for Livestock Production.. Biomolecules 2023 Mar 7;13(3).
- 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 Sep 29;9:130.
- Haritou SJ, Zylstra R, Ralli C, Turner S, Tortonese DJ. Seasonal changes in circadian peripheral plasma concentrations of melatonin, serotonin, dopamine and cortisol in aged horses with Cushing's disease under natural photoperiod.. J Neuroendocrinol 2008 Aug;20(8):988-96.
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