Hormonal Augmentation of Fertility in Sheep and Cattle 165 



In the cow there seems to be early partial loss (35), but with only 4 or 5 

 ovulations total loss has been noted at about half term (42) or earlier (9, 35). 

 In the cow therefore very close control is required over the number of 

 ovulations, but in the sheep this seems of little importance. 



OVULATION AND HEAT IN ANESTRUS 



Most workers have found that a single injection of FSH or of PMS will 

 induce ovulation in almost all treated sheep. Estimates of the time of ovula- 

 tion, based upon the time of slaughter and the appearance of the induced 

 corpora, range from 24 to 72 hr after injection, most commonly within 48 hr 

 (44, 61). A group of animals treated by Robinson (61) provide an exception; 

 some failed to ovulate even after two treatments with 800 i.u. PMS and there 

 does not seem to have been very much follicle growth. While some of these 

 animals were of a breed with a more restricted season than those usually 

 treated, all apparently had in common a poor nutritional status. 



After a single injection of FSH, PMS or PU the number of ovulations has 

 nearly always been within the normal range for the breed, and the ovulations 

 apparently occurred synchronously (34, 44). Instances have been noted of 

 two series of ovulations following a single injection of PMS : this may account 

 for multiple corpora lutea in some ewes so treated by Robinson (61). Casida 

 and colleagues (4, 54) have obtained multiple ovulations in anestrous sheep 

 with repeated FSH injections followed by LH; it seems unlikely that all the 

 ovulations were synchronous. 



Although the number of ovulations has been relatively constant, the extent 

 of follicle development has in general paralleled the dosage of FSH or PMS, 

 but this is by no means always obvious with PMS (44). 



Whereas a single gonadotropin treatment induces ovulation, this is rarely 

 accompanied by heat. Furthermore, artificial insemination has usually failed 

 to produce fertilization of the ova shed (41, 44). This has been attributed to 

 failure of sperm transport (58) and there is no reason to doubt the maturity 

 of the ova shed (5). 



The few sheep coming on heat have usually been found to have had a 

 corpus luteum regressing at about the time of injection and so have been not 

 anestrous in the strict sense. Two treatments with PMS, a cycle interval 

 apart, have been used to induce ovulation accompanied by fertile mating (18). 

 The success achieved has been very variable: sometimes very different results 

 have been obtained by the same workers in successive seasons (79). There is 

 no obvious reason for doubting that the second treatment also induces 

 ovulation: yet heat is often not shown. Gordon (34) obtained heat in only 

 4 of 59 ewes treated at 16-day intervals. Failure of proper luteal function has 

 been suggested, but Robinson (61) found no evidence for alteration of the 

 period of luteal function, and modifications of PMS dosage and of the 

 interval between treatments have met with no great success. 



