Daily rhythm of cortisol, and evidence for a photo-inducible phase for prolactin secretion in nonpregnant mares housed under non-interrupted and skeleton photoperiods.
Abstract: Studies were conducted in anestrous mares to characterize daily rhythms of cortisol in non-interrupted [ambient and 16 h light (L): 8 h dark (D)] and skeleton (10L:4D:2L:8D, 10L:6D:2L:6D and 10L:8D:2L:4D) photoperiods, and to determine if there exists a photosensitive phase for the secretion of prolactin. Neither peak or nadir concentrations of cortisol, nor the time of peak or nadir concentrations differed among photoperiod treatments. Highest concentrations (66 +/- 4.4 ng/ml, mean +/- SE) occurred between 0700 and 0900, whereas lowest concentrations (31 +/- 3.6 ng/ml) were found from 1900 to 2300. Mean daily concentrations of serum prolactin were significantly higher in mares housed under the 16L:8D and the 10L:8D:2L:4D photoperiods as compared with the remaining photoperiod treatments, and were lowest in the ambient photoperiod treatment. The mean daily concentration of prolactin in February among photoperiod treatments was inversely related to the number of days (from December 1) to first seasonal ovulation (r = -.92, P = .027). The results were interpreted to: 1) suggest that mares in the 10L:8D:2L:4D skeleton photoperiod do not phase-shift to interpret the 2-h light pulse as the beginning of their subjective day; and 2) provide further evidence that the photo-inducible phase for both prolactin secretion and the stimulation of seasonal reproductive activity occurs 8 to 10 h following the onset of the dark period (scotophase).
Publication Date: 1986-07-01 PubMed ID: 3733571DOI: 10.2527/jas1986.631169xGoogle Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- U.S. Gov't
- P.H.S.
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
The research article discusses the patterns of cortisol and prolactin secretion in horses based on different light-dark photoperiods. The aim is to understand if there’s an influence of light exposure on these hormones and to better comprehend the possible role of these hormonal rhythms in the regulation of reproductive activities in horses.
Overview of Study
- The research involved studying mares (female horses) in a state of anestrus, meaning they were not in their period of sexual receptivity or estrus.
- Various light-dark cycles were examined, both non-interrupted, with ambient light and a cycle of 16 hours of light and 8 hours of darkness, and skeleton photoperiods, with a short period of darkness interspersed between two segments of light exposure.
- One of the main objectives of the study was to find out if there was a specific photosensitive phase for the secretion of prolactin, a hormone that plays a key role in a variety of essential bodily functions, including reproduction.
Results of the Study
- Through the study, the researchers found that the peak and lowest concentrations of cortisol, and the time duration for these concentrations to occur, did not vary amongst the different photoperiod treatments.
- However, significant differences were noticed in the daily concentrations of serum prolactin based on the photoperiods. Increased secretion of prolactin was observed under 16 hours of light + 8 hours of darkness and 10 hours of light + 8 hours of darkness + 2 hours of light + 4 hours of darkness photoperiods, as compared to other photoperiod treatments. The lowest prolactin levels were found under the ambient light treatment.
- The researchers also found that the timing of the first seasonal ovulation in these mares in February was inversely related to mean daily concentration of prolactin among different photoperiod treatments. This means that the higher the prolactin levels, the fewer days were required to reach the first ovulation of the season.
Interpretation of Results
- The results suggested that the horses in the 10 hours of light + 8 hours of darkness + 2 hours of light + 4 hours of darkness photoperiod did not readjust their internal rhythm or timing in response to the additional 2-hour light pulse. They did not interpret it as the beginning of their ‘subjective day’.
- Further, the study provided evidence supporting the hypothesis that the increased secretion of prolactin and the triggering of seasonal reproductive activity occurred approximately 8 to 10 hours following the beginning of the dark period. This suggests that the onset of darkness plays an essential role in activating certain hormonal and reproductive processes in mares.
Cite This Article
APA
Johnson AL, Malinowski K.
(1986).
Daily rhythm of cortisol, and evidence for a photo-inducible phase for prolactin secretion in nonpregnant mares housed under non-interrupted and skeleton photoperiods.
J Anim Sci, 63(1), 169-175.
https://doi.org/10.2527/jas1986.631169x Publication
Researcher Affiliations
MeSH Terms
- Animals
- Circadian Rhythm
- Female
- Horses / physiology
- Hydrocortisone / blood
- Light
- Prolactin / blood
- Prolactin / metabolism
Grant Funding
- RR 07058-17 / NCRR NIH HHS
Citations
This article has been cited 4 times.- Rankins EM, Manso Filho HC, Malinowski K, McKeever KH. Muscular tension as an indicator of acute stress in horses. Physiol Rep 2022 Mar;10(6):e15220.
- Pawluski J, Jego P, Henry S, Bruchet A, Palme R, Coste C, Hausberger M. Low plasma cortisol and fecal cortisol metabolite measures as indicators of compromised welfare in domestic horses (Equus caballus). PLoS One 2017;12(9):e0182257.
- Fureix C, Benhajali H, Henry S, Bruchet A, Prunier A, Ezzaouia M, Coste C, Hausberger M, Palme R, Jego P. Plasma cortisol and faecal cortisol metabolites concentrations in stereotypic and non-stereotypic horses: do stereotypic horses cope better with poor environmental conditions?. BMC Vet Res 2013 Jan 7;9:3.
- 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.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
