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 6×6 Latin square design. Hormonal treatments were given as two simultaneous injections i.m. and consisted of: 1) 2ml propylene glycol and 2ml propylene glycol; 2) .5mg estradiol benzoate and 2ml propylene glycol; 3) .5mg estradiol benzoate and 4mg dexamethasone; 4) .5mg estradiol benzoate and 10mg progesterone; 5) .5mg estradiol benzoate and .4mg GnRH; and 6) .5mg estradiol benzoate and 12.5 mg testosterone propionate. The .5mg estradiol benzoate and 4mg dexamethasone treatment reduced the percentage of heifers in estrus compared with the .5mg estradiol benzoate and 2ml propylene glycol treatment. In Experiment 2, 16 ovariectomized heifers were used in four replicates of a 4×4 Latin square design to determine if pretreatment with progesterone potentiated the actions of estradiol. Hormonal treatments i.m. consisted of: 1) 0mg progesterone and .2mg estradiol benzoate; 2) 50mg progesterone and .2mg estradiol benzoate; 3) 0mg progesterone and .5mg estradiol benzoate; and 4) 50mg progesterone and .5mg 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.