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. 2015;26(4):147-50.
doi: 10.1294/jes.26.147. Epub 2016 Feb 3.

Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings

Takehiro Harada  1 , Yasuo Nambo  2 , Mutsuki Ishimaru  3 , Fumio Sato  4 , Kentaro Nagaoka  1 , Gen Watanabe  1 , Kazuyoshi Taya  5
Affiliations

Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings

Takehiro Harada et al. J Equine Sci. 2015.

Abstract

The effects of an extended photoperiod (EP) treatment (14.5 hr light, 9.5 hr dark) on Thoroughbred colts and fillies from December 25 at 7-9 months old to the following May at 12-14 months old on coat condition and gonadal functions were investigated. Coat condition was evaluated in April. The colts and fillies in the EP treatment group changed from winter to summer coats (molting of winter coats), whereas those in the control group did not. To determine the day of first ovulation, the plasma concentrations of progesterone were measured once a month in fillies. The day of first ovulation was advanced in the EP treatment fillies compared with the control fillies. The present study clearly demonstrated that the EP treatment advanced the molting of winter coats and advanced ovulation in fillies, even in weanlings.

Keywords: Thoroughbred weanling; extended photoperiod treatment; gonadal function; molting of winter coat; progesterone.

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Figures

Fig. 1.
Fig. 1.
Comparison of the hair coat conditions of representative colts (A, B) and fillies (C, D) in the control group (A, C) and extended photoperiod treatment group (B, D) in April at one year old.
Fig. 2.
Fig. 2.
Comparison of scores of hair coat condition between the extended photoperiod treatment group (EP, □) and control group (Control, ■) in April. Results are expressed as the mean ± SEM. *P<0.05.
Fig. 3.
Fig. 3.
Changes in plasma concentrations of progesterone (A, B) in individual Thoroughbred fillies in the control (A) and extended photoperiod treatment groups (B) from December at the weanling stage to May at the yearling stage. Letters represent the first letter of each month.
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