Hormonal Augmentation of Fertility in Sheep and Cattle 175 



and increasing release of hormone would appear probable, such as might 

 occur if its secretion rate were inversely related to the level of circulating 

 progesterone. 



Consistently to obtain multiple ovulation artificially one depends upon 

 luteal — or progesterone — restraint of the ovulating discharge. In the normal 

 breeding season of the sheep, lengthening of the cycle — and so, perhaps, of 

 luteal function — is associated with increased ovulation rate. In ruminants 

 at least, the factors regulating follicle growth seem at the present time scarcely 

 separable from those governing luteal function. 



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