Alteration of the Estrual Cycle by Pituitary Gonadotropins and Persistence of the Effects upon Reproductive Performance in Ewes

Abstract
The effects of two gonadotropic extracts of the pituitary gland were compared when administered to ewes in three stages of the estrual cycle—fourth, eighth, and twelfth days. Four subcutaneous injections of follicle-stimulating extract in one case and of unfractionated extract in the other were used, each being followed by one intravenous injection of unfractionated extract. Thirty ewes were studied in the experiment. Treatment with unfractionated extract increased both the length and variation of the estrual cycles during which treatment was begun. There was no evident effect of follicle-stimulating extract upon the current estrual cycle when treatment was begun on the fourth or the twelfth days; the variation was increased, however, when treatment was begun on the eighth day of the cycle. Treatment with either extract shortened the first estrual period subsequent to the end of treatment in the four- and eight-day groups, but in the twelve-day groups the periods were shorter for the unfractionated and longer for the follicle-stimulating extract than for the controls. Ten ewes conceived from 20 inseminations among the 15 animals receiving unfractionated extract and 14 ewes from 19 inseminations among a like number receiving follicle-stimulating extract. Breeding was begun at the first estrus subsequent to the end of treatment. Neither extract gave any practical gain in controlling the time of estrus so that variation in the time of breeding could be decreased. In general, greater physiological disturbances followed the use of unfractionated than of follicle-stimulating extract. Copyright © . .

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