Effect of Reason and Artificial Photoperiod on Levels of Estradiol-17β and Estrone in Blood Serum of Stallions

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Abstract
Five stallions were subjected to a gradually increasing photoperiod beginning on October 15. Maximum daylength (16 hr) occurred on February 8 and was maintained until October 6. Four stallions were kept under the natural photoperiod. Four samples of jugular blood were drawn at 20-min intervals from each stallion once or twice per month from November 6 to November 5. Estradiol-17β (E2) averaged 79 pg/ml in serum from control stallions and 63 pg/ ml in light-treated stallions (P>.05). Mean E2 levels in control stallions varied (P<.05) over time and averaged 128 pg/ml during late April as compared to 60 to 90 pg/ml from June through March. Stallions exposed to the artificial photoperiod exhibited no increase in E2 levels. Estrone (E1) averaged 132 pg/ml in serum from control stallions and 203 pg/ml in treated stallions (P>.05). Mean levels of E1 in control stallions varied (P<.05) over time, although no seasonal trend was evident. The pattern of E1 levels for the treated stallions did not differ (P>.05) from that of control stallions. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.