The Effect of Progesterone on the Estrous Response of Estrogen-Conditioned Ovariectomized Cows

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Abstract
Pro-gesterone can induce estrus behavior, including sexual receptivity in the estrogen-conditioned ovariectomized cow. Maximal synergistic action of progesterone was observed when this hormone was injected 12 hours before, simultaneously with, or 12 hours following a conditioning level of estrogen. It is suggested that after conditioning with female sex hormone, normal sexual receptivity in the cow may be caused by the action of progesterone produced during the period of the pre-ovula-tory development of the Graafian follicle. Progesterone in large doses can antagonize the estrus behavior response in ovariectomized cows injected with a level of estrogen which would otherwise induce sexual receptivity. Estrogen-treated cows injected with 30 mg or more of progesterone failed to show signs of estrus. Desoxycorticosterone acetate and testosterone propionate both show a synergistic action in estrogen-conditioned ovariectomized cows.