title: 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.
authors: Donan NOSAI, Hokkaido 049-3521, Japan.
authors: Tsuyoshi
authors: T
authors: Suzuki
authors: Ritto Training Center, Japan Racing Association, Shiga 520-3085, Japan.
authors: Hirotoshi
authors: H
authors: Mizukami
authors: 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.
authors: Yasuo
authors: Y
authors: Nambo
authors: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors: Mutsuki
authors: M
authors: Ishimaru
authors: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors: Kenji
authors: K
authors: Miyata
authors: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors: Kentaro
authors: K
authors: Akiyama
authors: Miyazaki Yearling Training Farm, Japan Racing Association, Miyazaki 880-0036, Japan.
authors: Kenji
authors: K
authors: Korosue
authors: Equine Department, Japan Racing Association, Tokyo 105-0003, Japan.
authors: Hiroshi
authors: H
authors: Naito
authors: 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.
authors: Kentaro
authors: K
authors: Nagaoka
authors: 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.
authors: Gen
authors: G
authors: Watanabe
authors: 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.
authors: Kazuyoshi
authors: K
authors: Taya
keywords: Thoroughbred colt and filly; climate; extended photoperiod treatment; growth; testis and ovary