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Home / Equine Research Bank / J Equine Sci / Effects of an extended photoperiod on gonadal function and c...
Journal of equine science2015; 26(2); 57-66; doi: 10.1294/jes.26.57

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies.

Abstract: The effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17β and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17β and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.
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Publication Date: 2015-07-02 PubMed ID: 26170762PubMed Central: PMC4496423DOI: 10.1294/jes.26.57Google Scholar: Lookup
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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 observed the influence of extended photoperiod (EP), longer periods of light exposure, on one to two-year-old Thoroughbred colts and fillies. It found that EP encourages the onset of winter coat shedding and advanced development in gonadal function which appeared to be due to an elevation in prolactin hormone levels.

Methods and Participants

  • The study involved 62 Thoroughbred horses, 31 colts and 31 fillies, raised at the Hidaka Training and Research Center in Japan.
  • 30 of the horses (15 colts and 15 fillies) were exposed to an extended photoperiod from December 20 to April 10, while the remaining 32 served as a control group and only received natural light.
  • The extended photoperiod was delivered using a 100-watt white bulb and consisted of an artificially created light and dark cycle of 14.5 hours and 9.5 hours respectively.
  • Monthly blood samples were collected from each horse from October at year one to February at year two. After March, blood samples were collected twice a month in colts and weekly in fillies.
  • For gauging the coat condition, an evaluation was conducted in January and April on 56 horses.

Findings

  • No significant difference was observed in coat conditions between the control and EP group in January. However, by April, the EP group exhibited a transition from winter to summer coats, unlike the control group.
  • Regarding endocrine changes, there was a marked increase of prolactin, follicle-stimulating hormone (FSH), inhibin, and testosterone in EP colts from January to April as compared to control group. Also, luteinizing hormone (LH) levels were observed to rise in the EP colts.
  • The EP fillies showed notably higher prolactin, LH, inhibin, estradiol-17β, and progesterone plasma concentrations throughout January to April. However FSH was higher in control group fillies in January.
  • EP caused an advancement in ovulation day for fillies compared to control group.

Conclusion

  • The study revealed that extended photoperiods can stimulate the early shedding of winter coats in both colts and fillies. This effect is believed to be due to an increase in the action of prolactin triggered by the EP treatment.
  • In addition, EP appeared to activate the hypothalamus-pituitary-gonadal axis in juvenile horses, advancing ovulation in fillies.
  • As such changes were within the physiological range, and the method was safe and simple to implement, the research suggests that EP treatment could be an effective technique in horse husbandry.

Cite This Article

APA
Kunii H, Nambo Y, Okano A, Matsui A, Ishimaru M, Asai Y, Sato F, Fujii K, Nagaoka K, Watanabe G, Taya K. (2015). Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies. J Equine Sci, 26(2), 57-66. https://doi.org/10.1294/jes.26.57

Publication

Journal of equine science
ISSN: 1340-3516
NlmUniqueID: 9503751
Country: Japan
Language: English
Volume: 26
Issue: 2
Pages: 57-66

Researcher Affiliations

Kunii, Hirokazu
  • The Horse Racing School, Japan Racing Association, Chiba 270-1431, Japan.
Nambo, Yasuo
  • Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan ; United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.
Okano, Atsushi
  • Miho Training Center, Japan Racing Association, Ibaraki 300-0493, Japan.
Matsui, Akira
  • Equine Research Institute, Japan Racing Association, Tochigi 320-0856, Japan.
Ishimaru, Mutsuki
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
Asai, Yo
  • Miho Training Center, Japan Racing Association, Ibaraki 300-0493, Japan.
Sato, Fumio
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
Fujii, Kazuki
  • United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan.
Nagaoka, Kentaro
  • United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan.
Watanabe, Gen
  • United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan.
Taya, Kazuyoshi
  • Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan ; Shadai Corporation, Hokkaido 059-1432, Japan.

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This article has been cited 11 times.
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  5. Harada T, Nambo Y, Ishimaru M, Sato F, Nagaoka K, Watanabe G, Taya K. Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings. J Equine Sci 2015;26(4):147-50.
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