title: Comparison of growth and endocrine changes in Thoroughbred colts and fillies reared under different climate conditions.
abstract: Development and endocrine changes in Thoroughbreds colts and fillies were compared between those reared at two facilities of the Japan Racing Association, the Hidaka Training and Research Center (Hidaka) and Miyazaki Yearling Training Farm (Miyazaki). Thoroughbred colts and fillies born in Japan between 2003 and 2010 were used. Each colt group and filly group was divided into 2 groups, respectively, and raised in Hidaka or Miyazaki for 7 months from September at 1 year old to April at 2 years old. For the growth parameters, the body weight, height at withers, and girth and cannon circumferences were measured once a month. For parameters of endocrine function, circulating prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin-like growth factor-1 (IGF-1), testosterone, progesterone, and estradiol-17β levels were measured. Regarding growth, the rate of increase over the 7-month period was significantly higher in both colts and fillies raised in Miyazaki than in Hidaka in all 4 parameters: body weight, height at withers, and girth and cannon circumferences. The endocrine changes of the colts and fillies born in 2007 were as follows. In colts, although circulating prolactin tended to be higher in colts reared in Hidaka from October to April, circulating LH, FSH, testosterone, estradiol-17β and IGF-1 tended to be higher in colts reared in Miyazaki than in Hidaka, suggesting that the gonadotropin-releasing hormone-LH/FSH system and the growth hormone-IGF-1 system were more active in colts reared in Miyazaki as compared with those reared in Hidaka. In fillies, circulating prolactin tended to be higher in fillies reared in Hidaka in February and March, but no significant difference was noted in the serum LH, FSH, IGF-1, or progesterone level between the 2 groups. Circulating estradiol-17β tended to be higher in fillies reared in Miyazaki than in Hidaka in October and November. Regarding ovarian function, the initial ovulation occurred by the end of March in 2 (16.7%) of 12 fillies reared in Hidaka and 7 (38.9%) of 18 fillies reared in Miyazaki, suggesting that the ovarian function was more active in fillies reared in Miyazaki as compared with those reared in Hidaka. Based on these findings, it was clarified that development of the body and gonads was faster in Miyazaki compared with Hidaka in both colts and fillies.
authors.affiliation: Ritto Training Center, Japan Racing Association, Shiga 520-3085, Japan.
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Mizukami
authors.affiliation: Donan NOSAI, Hokkaido 041-1214, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: 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.forename: Yasuo
authors.initials: Y
authors.lastname: Nambo
authors.affiliation: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors.forename: Mutsuki
authors.initials: M
authors.lastname: Ishimaru
authors.affiliation: Equine Department, Japan Racing Association, Tokyo 106-8401, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Naito
authors.affiliation: Miyazaki Yearling Training Farm, Japan Racing Association, Miyazaki 880-0036, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Korosue
authors.affiliation: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Akiyama
authors.affiliation: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Miyata
authors.affiliation: Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yamanobe
authors.affiliation: 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.forename: Kentaro
authors.initials: K
authors.lastname: Nagaoka
authors.affiliation: 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.forename: Gen
authors.initials: G
authors.lastname: Watanabe
authors.affiliation: 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.forename: Kazuyoshi
authors.initials: K
authors.lastname: Taya
keywords: Thoroughbred colt and filly; climate; growth; ovary; testis