title: Seasonal changes in serum progesterone levels in Thoroughbred racehorses in training.
abstract: The objective of the present study was to verify the seasonal luteal activity of racehorses in training in Japan from March to August. We allocated 102 horses into a luteal activity group and non-luteal activity group. The luteal activity group included horses with serum progesterone levels that were consistently >1 ng/ml and changed by ± 1 ng/ml. In contrast, the progesterone levels of the non-luteal activity group were consistently <1 ng/ml. In late spring (from May 1 to June 30) and summer (from July 1 to August 31), the percentage of horses in the luteal activity group was significantly higher than in early spring (from March 1 to April 30, P<0.01). These findings demonstrate clear seasonal variations in ovarian activity. The present study also suggest that training for a race may not affect ovarian activity in female racehorses.
authors: Racehorse Clinic, Ritto Training Center, Japan Racing Association, Shiga 520-3085, Japan; Present address: Sports Science Division, Equine Research Institute, Japan Racing Association, Tochigi 320-0856, Japan.
authors: Yuji
authors: Y
authors: Takahashi
authors: Racehorse Clinic, Ritto Training Center, Japan Racing Association, Shiga 520-3085, Japan.
authors: Makoto
authors: M
authors: Akai
authors: Equine Science Division, Hidaka Training and Research Center, Japan Racing Association, Hokkaido 057-0171, Japan.
authors: Harutaka
authors: H
authors: Murase
authors: Department of Clinical Veterinary Sciences, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan.
authors: Yasuo
authors: Y
authors: Nambo
keywords: progesterone; racehorse; seasonal change