Sexual behaviour was not induced in ovariectomized cows by single doses of 100 or 250 pg oestradiol benzoate or by 3 injections of 50 \g=m\g oestradiol benzoate given at 12-h intervals. Treatment with 3 doses of 250 or 500 \g=m\g oestradiol benzoate at 12-h intervals produced plasma levels that were similar to those during pro-oestrus and oestrus in intact cows, and 11 of 12 treated animals showed oestrous behaviour. The higher dose resulted in a more pronounced response in 'mounting' and

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... ed' behaviour and a shorter interval to the onset of behavioural signs of oestrus. Oestrous behaviour was not observed in any ovariectomized cows treated with 1, 2 or 20 mg testosterone propionate, doses that resulted in plasma levels comparable to those in intact pro-oestrous animals. Treatment with pharmacological doses of testosterone propionate resulted in transient mounting and interest in similarly treated females, but the results were inconsistent.