Hormonal Augmentation of Fertility in Sheep and Cattle 169 



after massive or prolonged treatment (9, 29), but Folley and Malpress (31) 

 found this condition transitory; a persistent cystic condition, such as some- 

 times occurs in infertile cows, was not produced. 



Follicles developed by PMS or FSH in the presence of a corpus luteum do 

 not in general ovulate spontaneously; one may suppose that progesterone 

 blocks an endogenous ovulating release of hormone. The blockage is probably 

 not absolute, for estrogen can induce midcycle ovulation (sheep, 44). Con- 

 ceivably a partial pituitary "escape" might cause ovulation, or, being 

 inadequate for that, be enough to luteinize a follicle or make it cystic. 

 However, "shock" ovulations (or abortive attempts at ovulation) might also 

 be due to a sudden rise in the level of gonadotropin circulating; and would 

 then presumably be more likely with larger doses, greater ease of absorption 

 (or intravenous administration), and with greater luteinizing activity of the 

 material used — with FSH rather than with PMS. 



AFTER REMOVAL OF THE CORPUS LUTEUM 



Haimnond and Bhattacharya (43) found that, when given to cows at or 

 after the time of corpus luteum removal, PMS and FSH could induce twin 

 or multiple ovulations, but in about 50% only one egg was shed. They found 

 that the times of heat and of ovulation were advanced. Rowson (71), however, 

 often found delay or failure to ovulate when he gave purified PMS at 

 expression of the corpus luteum, and subsequent treatment with PU often 

 did not induce ovulation. Umbaugh (75) reports that FSH in subcutaneous 

 waxy implants, made when the corpus luteum was removed, did not produce 

 multiple ovulation; but many follicles were observed to ovulate within about 

 30 hr when the same material was given again four days later, this time 

 intravenously. 



From small series of cows given PMS at two dose levels 0-5 days before 

 expression of the corpus luteum Hammond and Bhattacharya (43) concluded 

 that, in general, the longer the interval between doses and the larger the dose, 

 the greater was the number of ovulations and the shorter the interval to 

 ovulation after expression of the corpus luteum. However, they noted on the 

 one hand animals in which a large dose produced little follicle growth, and 

 on the other, multiple ovulations from a small dose. Modification of dosage 

 and interval failed to yield twin ovulations consistently (42). 



This procedure was also technically unsatisfactory for producing multiple 

 ovulations because of the risk of damaging follicles when expressing the 

 corpus luteum. Follicles which were ruptured or bruised sometimes luteinized 

 and then might block further ovulation. 



Dowling (25) used this same procedure to produce muhiple ovulations 

 both with FSH and with purified PMS. He found the interval to heat was 

 in most cases decreased. Whereas most ova were fertilized after FSH, very 

 few were cleaved in PMS-treated animals. This may be related to greater 



