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Efficacy of Oral Estradiol 17-ß for Growing and Fattening Steers^{1, 2,}

University of Arizona, Tucson 85721

Abstract

Three growing and two fattening trials were conducted to determine the effect of various oral levels of the natural basic estrogen, estradiol 17-ß (E₂), on feedlot performance of steers. In one growing trial with steers fed a 30% concentrate ration, a 40 mg daily feeding level of E₂ or a 10 mg feeding level of diethylstilbestrol (DES) increased (P < .05) gains 18 and 22%, respectively. The feed requirements were reduced (P < .05) by 11 and 15%, respectively, on the E₂ and DES treatments as compared to the control. In the same trial, feeding a 10 mg level of E₂ did not improve gain but decreased (P < .05) feed requirements 5.3% compared to the controls. In one growing trial, response to a 15 mg feeding level of E₂ was approximately one-half that of either 10 mg oral DES, a 12 mg DES implant or a 36 mg Ralgro implant. The response of the 15 mg oral E₂ feeding level was significantly greater (P < .05) than that of the control but not different (P >.05) from the two DES treatments but less (P < .05) than the Ralgro treatment. In a third growing trial, 40 mg of E₂ increased gain (P < .05) by 11% over the control steers.

One fattening trial was conducted at Tucson with four levels of E₂ (10, 20, 40 and 80 mg), utilizing a 90% concentrate ration. Gain was improved 12 and 20% with 40 and 80 mg feeding levels of E₂, respectively, compared to a 13% response when 20 mg of DES was fed. Gain response to the two levels of E₂ and the DES was greater (P < .05) than that of controls. Daily gain was the highest on the 80 mg E₂ feeding level but not different (P > .05) from the 40 mg E₂ or the 20 mg oral DES feeding levels. Feed requirements per unit gain paralleled daily gain. The dose response for the four E₂ treatments was linear (P < .01) over the range of levels tested.

In the second feeding trial conducted at the Yuma station neither a 20 mg oral level of DES nor a 40 mg oral level of E₂ significantly (P > .05) improved performance over the control although gains on the 20 mg oral DES and the 40 mg oral E₂ were 9 and 5% greater, respectively, that that of the control. The lack of response may be related to the effect of climatic heat stress during the summer months.

¹ Arizona Agricultural Experiment Station Technical Paper 2035.

² Animals were marketed in cooperation with the Food and Drug Administration and the United States Department of Agriculture under rules and regulations covering new animal drugs for investigational use.