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Effect of the Interval between Withdrawal of Progestagen Pessaries and Time of PMS Administration on Oestrus and Ovulation in Cyclic Ewes

J. F. Roche
Irish Journal of Agricultural Research
Vol. 7, No. 1 (Apr., 1968), pp. 1-6
Stable URL: http://www.jstor.org/stable/25555460
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Effect of the Interval between Withdrawal of Progestagen Pessaries and Time of PMS Administration on Oestrus and Ovulation in Cyclic Ewes
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Abstract

Pessaries containing 20 mg fluorogestone acetate (SC-9880) were administered intravaginally to 125 (mainly crossbred) ewes of varying ages. The ewes were allotted randomly on a basis of breed and age to four groups of approximately equal numbers. Three groups received 5 IU PMS per lb body weight at one of the following intervals: 4 days before withdrawal of the pessary (-4 days), 2 days before (-2 days) and at the time of pessary withdrawal (0 days). The fourth group received the pessaries alone. All ewes were bred to Suffolk rams of known fertility at the controlled oestrus and allowed to proceed to lambing. Time of PMS treatment affected the interval from pessary withdrawal to onset of oestrus but not the duration of oestrus. The ovulation rate was significantly higher in groups given PMS at -4 days and -2 days than in the 0-day and the no-PMS groups. The lambing rates followed a similar pattern although, with the numbers available, the differences did not attain statistical significance.

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