Abstract
The effect on fertility of the amount of Cronolone (Searle) absorbed from intravaginal sponges and the method of artificial insemination was studied. A significant linear relationship exists between fertility and the amount absorbed in 16 days, over the range 1-10 mg. No such relationship can be demonstrated above this amount, and great variability and sensitivity to failure of fertility is shown at all dose levels. Insemination on a fixed time basis is superior to that on teasing. Of ewes inseminated on a time basis on the second or third day after withdrawal of sponges, 117 lambed of 237 treated (49.4%). Of ewes inseminated on detection of oestrus, 97 lambed of 196 in oestrus (49.5 %) of 249 treated (39 .O %).

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