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Journal of equine science2016; 26(4); 113-124; doi: 10.1294/jes.26.113

Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions.

Abstract: One- to two-year-old Thoroughbred colts and fillies being reared in Miyazaki (warm climate) and Hidaka (cold climate), Japan, were administered extended photoperiod (EP) treatment between December 20 and the following April 10, and its effect on growth, endocrine changes, gonadal activation, and hair coat condition was investigated. In colts reared in Miyazaki, no effect of EP treatment was noted on the growth indices, including body weight (BW), height at withers (HW), girth, and cannon circumference (CC), whereas the BWs and CCs of fillies were significantly higher in the EP treatment group than the control. In Hidaka, the BWs and HWs of colts and HWs of fillies were significantly higher in the EP treatment group. Gonadal activation characterized by an increase in circulating hormone concentrations was earlier in the EP treatment group for fillies reared in Miyazaki [luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17β (E2)] and in colts (LH, testosterone, and E2) and fillies (LH, FSH, P4, and E2) reared in Hidaka. Regardless of sex and climate, prolactin was significantly higher in the EP treatment group, whereas insulin-like growth factor (IGF-I) was not. Initial ovulation occurred before April in more of the EP treatment group than the control regardless of the climate. Molting of the hair coat, examined in March, was advanced in the EP treatment group regardless of sex and climate. These results suggest that EP treatment may promote growth and gonadal activation in fillies reared in Miyazaki and in colts and fillies reared in Hidaka and that the effect may be mediated by prolactin.
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Publication Date: 2016-02-03 PubMed ID: 26858576PubMed Central: PMC4739141DOI: 10.1294/jes.26.113Google Scholar: Lookup
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  • Journal Article

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 examines the effect of extended photoperiod or increased light exposure on the growth, endocrine changes, reproductive function, and coat condition of Thoroughbred yearlings in different climates: a warm climate (Miyazaki, Japan) and a cold climate (Hidaka, Japan).

Methods and Subjects

  • The research subjects were Thoroughbred colts and fillies aged 1-2 years in Miyazaki and Hidaka.
  • The research utilized extended photoperiod (EP) treatment on these young horses from December 20 until April 10.

Results on Growth Indices

  • In Miyazaki, extended photoperiod exposure had no significant effect on the growth indices of the colts, including body weight, height at withers, girth, and cannon circumference.
  • However, in fillies from Miyazaki, body weights and cannon circumferences were significantly higher when an extended photoperiod was implemented than when no treatment was applied.
  • In Hidaka, both colts and fillies showed significantly higher body weights and heights at withers when under the extended photoperiod treatment as compared to controls.

Results on Endocrine Changes and Gonadal Activation

  • There was earlier gonadal activation—measured by increased hormone concentrations—in horses subject to the EP treatment.
  • This was observed in fillies in Miyazaki, and in both colts and fillies in Hidaka.
  • Prolactin levels were significantly higher in the EP treatment group in both climates, regardless of the sex of the horse, but the insulin-like growth factor didn’t show a significant difference.
  • Initial ovulation, noted before April, was more prevalent in the EP treatment group regardless of the climate.

Results on Hair Coat Condition

  • The study noted that molting of the hair coat, observed in March, was more advanced in horses under the EP treatment across both sexes and both climates.

Conclusion

  • The findings suggest that extended photoperiod may promote growth and stimulate reproductive activity in fillies in a warmer climate (Miyazaki) and in both colts and fillies in a colder climate (Hidaka).
  • Prolactin, a hormone that significantly increased with the EP treatment, may mediate these effects.

Cite This Article

APA
Suzuki T, Mizukami H, Nambo Y, Ishimaru M, Miyata K, Akiyama K, Korosue K, Naito H, Nagaoka K, Watanabe G, Taya K. (2016). Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions. J Equine Sci, 26(4), 113-124. https://doi.org/10.1294/jes.26.113

Publication

Journal of equine science
ISSN: 1340-3516
NlmUniqueID: 9503751
Country: Japan
Language: English
Volume: 26
Issue: 4
Pages: 113-124

Researcher Affiliations

Suzuki, Tsuyoshi
  • Donan NOSAI, Hokkaido 049-3521, Japan.
Mizukami, Hirotoshi
  • Ritto Training Center, Japan Racing Association, Shiga 520-3085, 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.
Ishimaru, Mutsuki
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
Miyata, Kenji
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
Akiyama, Kentaro
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
Korosue, Kenji
  • Miyazaki Yearling Training Farm, Japan Racing Association, Miyazaki 880-0036, Japan.
Naito, Hiroshi
  • Equine Department, Japan Racing Association, Tokyo 105-0003, 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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Citations

This article has been cited 5 times.
  1. Ishimaru M, Matsui A, Seki K, Korosue K, Akiyama K, Mizukami H, Yoshida T, Taya K. Effects of different winter climates in Japan on body composition of young Thoroughbreds in training. J Vet Med Sci 2022 Nov 18;84(12):1585-1594.
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  2. Tangyuenyong S, Sato F, Nambo Y, Murase H, Endo Y, Tanaka T, Nagaoka K, Watanabe G. Comparison of physical body growth and metabolic and reproductive endocrine functions between north and south climates of Japan in trained Thoroughbred yearling horses. J Equine Sci 2017;28(3):77-86.
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  3. Toishi Y, Tsunoda N, Kume K, Nagaoka K, Watanabe G, Taya K. PATHFAST, a novel chemiluminescent enzyme immunoassay for measuring estradiol in equine whole blood and serum. J Reprod Dev 2016 Dec 20;62(6):631-634.
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  4. 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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  5. Ishimaru M, Okano A, Matsui A, Murase H, Korosue K, Akiyama K, Taya K. Effects of an extended photoperiod on body composition of young Thoroughbreds in training. J Vet Med Sci 2024 Jan 10;86(1):58-65.
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