The effect of Enovid, the well-known contraceptive agent, on the lactation performance has been studied in the mouse, the rat and the rabbit. Two dose levels were employed, one corresponding to twice the human dose, on the basis of mg/kg body weight and the other equivalent to twenty times the human dose. Growth curve of the litter was used as an index of efficacy of lactation. It was observed that, in rats, the steroid at both the dose levels caused 10 to 20% inhibition in growth rate of the young, while in rabbits there was an enhancement. The compound did not seem to have any effect on the lactation of mice. The amount of inhibition or enhancement was not related to the dose employed. The reasons for the differential response in the three species have been discussed.
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