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. 2015;26(4):135-9.
doi: 10.1294/jes.26.135. Epub 2016 Feb 3.

Seasonal Changes in Serum Progesterone Levels in Thoroughbred Racehorses in Training

Free PMC article

Seasonal Changes in Serum Progesterone Levels in Thoroughbred Racehorses in Training

Yuji Takahashi et al. J Equine Sci. .
Free PMC article


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.

Keywords: progesterone; racehorse; seasonal change.


Fig. 1.
Fig. 1.
Representative examples of each group. The dotted line indicates 1 ng/ml, and the dashed, thin, and thick lines indicate the non-luteal activity, persistent corpus luteum, and ovulation types, respectively. The serum progesterone levels of the non-luteal activity type and the persistent corpus luteum type were consistently lower and higher than 1 ng/ml during 4 weeks, respectively. The levels of the ovulation type showed a change from less than 1 ng/ml to more than 1 ng/ml during 4 weeks.

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    1. Aurich C. 2011. Reproductive cycles of horses. Anim. Reprod. Sci. 124: 220–228. - PubMed
    1. Beals K.A., Meyer N.L. 2007. Female athlete triad update. Clin. Sports Med. 26: 69–89. - PubMed
    1. Bonen A., Ling W.Y., MacIntyre K.P., Neil R., McGrail J.C., Belcastro A.N. 1979. Effects of exercise on the serum concentrations of FSH, LH, progesterone, and estradiol. Eur. J. Appl. Physiol. Occup. Physiol. 42: 15–23. - PubMed
    1. Brown-Douglas C.G., Firth E.C., Parkinson T.J., Fennessy P.F. 2004. Onset of puberty in pasture-raised Thoroughbreds born in southern hemisphere spring and autumn. Equine Vet. J. 36: 499–504. - PubMed
    1. Bullen B.A., Skrinar G.S., Beitins I.Z., von Mering G., Turnbull B.A., McArthur J.W. 1985. Induction of menstrual disorders by strenuous exercise in untrained women. N. Engl. J. Med. 312: 1349–1353. - PubMed

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