Influence of dexamethasone, progesterone, gonadotropin-releasing hormone, and testosterone on estrous behavior of estradiol-treated ovariectomized heifers.

In Experiment 1, 12 ovariectomized heifers were assigned to receive weekly hormone treatments in a replicated 6 x 6 Latin square design. Hormonal treatments were given as two simultaneous injections i.m. and consisted of: 1) 2 ml propylene glycol and 2 ml propylene glycol; 2) .5 mg estradiol benzoate and 2 ml propylene glycol; 3) .5 mg estradiol benzoate and 4 mg dexamethasone; 4) .5 mg estradiol benzoate and 10 mg progesterone; 5) .5 mg estradiol benzoate and .4 mg GnRH; and 6) .5 mg estradiol benzoate and 12.5 mg testosterone propionate. The .5 mg estradiol benzoate and 4 mg dexamethasone treatment reduced the percentage of heifers in estrus compared with the .5 mg estradiol benzoate and 2 ml propylene glycol treatment. In Experiment 2, 16 ovariectomized heifers were used in four replicates of a 4 x 4 Latin square design to determine if pretreatment with progesterone potentiated the actions of estradiol. Hormonal treatments i.m. consisted of: 1) 0 mg progesterone and .2 mg estradiol benzoate; 2) 50 mg progesterone and .2 mg estradiol benzoate; 3) 0 mg progesterone and .5 mg estradiol benzoate; and 4) 50 mg progesterone and .5 mg estradiol benzoate. Progesterone pretreatment, at either dosage of estradiol benzoate, did not increase the percentage of heifers in estrus. Based on these observations, we conclude that: 1) dexamethasone inhibited estrus in estradiol-treated ovariectomized heifers and 2) progesterone pretreatment did not potentiate the actions of estradiol in ovariectomized heifers.