HORMONAL AUGMENTATION OF FERTILITY 

 IN SHEEP AND CATTLE 



John Hammond, Jr. 

 Cambridge University School of Agriculture 



INTRODUCTION 



A QUARTER of a century has passed since Cole and Miller (18) used gonado- 

 tropin to obtain fertility in anestrous sheep. In reviewing the progress which 

 has been made since then, I intend to deal principally with the control of 

 ovulation and estrous behavior, largely neglecting the many other factors — 

 including fertilization and fetal loss — that intervene between mating and 

 weaning. 



Hormonal control of ovulation has potential agricultural uses in two main 

 fields. Given a satisfactory technique of transplantation, there will be genetic 

 applications such as the multiplication of offspring from particular dams, and 

 the acceleration of a breeding program by production of young from im- 

 mature females. This might find wide application, but yet could be worth- 

 while on a small scale. The other type of application, increasing the number 

 of young born, is only likely to be worthwhile if it can be carried out widely 

 and cheaply. 



For this reason most investigators have used the gonadotropins of pregnant 

 mare serum (PMS) and human pregnancy urine (PU). Those workers who 

 have employed pituitary extracts have generally administered predominantly 

 follicle-stimulating preparations subcutaneously, and given LH-rich extracts 

 intravenously. To avoid cumbersome phraseology, I shall use the (inaccurate) 

 terms "FSH" and "LH" in referring to these pituitary extracts. Unless other- 

 wise specified, it should be understood that PMS and "FSH" have been 

 given subcutaneously and PU and "LH" intravenously. 



While PMS hormone circulates in the mare in enormous quantity, a 

 succession of follicles develop and ovulate (70) ; yet the urinary estrogen is 

 not obviously raised (17) and relatively small amounts of exogenous estrogen 

 given at this time will induce abortion (21). Thus PMS appears to have the 

 properties ascribed by Simpson, Li and Evans (72), in 1951, to purified FSH. 

 In all the work with farm animals one has to allow for endogenous hormone 

 production comiplicating the response; on the other hand, we may perhaps 

 be allowed the simplification of regarding PMS as a pure type of FSH. 



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