Hormonal Augmentation of Fertility in Sheep and Cattle 173 



experiment the lambing percentage was not significantly raised, but there 

 was no reduction of conception rate. Rowson (71) found that progesterone 

 given after removal of the corpus luteum protected follicles stimulated by 

 PMS from loss of capacity to ovulate. It seems therefore that this type of 

 treatment offers considerable prospects of success. 



OVULATION BEFORE PUBERTY 



The ruminant ovary contains Graafian follicles at birth. Mansour (50) 

 gave a single dose of PMS to lambs at different ages and observed increasing 

 response with increase of age and of body weight. One-week-old animals 

 showed no obvious follicle growth, later there were luteinized follicles, and 

 later still ovulations. Progesterone treatment preceding PMS enhanced the 

 response. 



Ovulation in calves, sometimes multiple, has been obtained with repeated 

 FSH followed by LH (9, 10). Marden (51) noted greater frequency of multiple 

 ovulations after two treatments, and seems to have had some success with a 

 single series preceded by progesterone. Similar treatment by Black et al. (6) 

 did not noticeably enhance the ovulation rate. 



So far as one can tell, the response before puberty does not differ from the 

 extremes of response found in anestrus. 



OTHER POSSIBILITIES 



So far administration of gonadotropins has mainly been considered. 

 Steroid, or other, stimulation of endogenous gonadotropin secretion might, 

 if practicable, well prove cheaper than administration of PMS. 



Induction of ovulation in anestrous sheep by progesterone has already 

 been mentioned. In sheep in which the cycle was prolonged with progesterone 

 the ovulation rate tended to be decreased (28), though in the sow (3) an 

 increase has been noted. 



Estrogen implants given to induce lactation in cattle (20) inhibited the 

 ovarian cycle, which was not immediately resumed upon cessation of treat- 

 ment. There was a period of cystic follicle formation followed by one in 

 which twin ovulations, and calvings, were more frequent than normally. 



The cyst formation one may attribute to failure of pituitary hormone 

 reserves for ovulation to be accumulated in the absence of a corpus luteum. 

 In the treatment of chronic cysts in cattle (39) the cyst is ruptured and a 

 fresh follicle develops which is itself liable to become cystic. But this follicle 

 may be induced to ovulate by PU (43) or to luteinize by manual rupture 

 before the granulosa degenerates. Thereafter a normal cycle is resumed. 

 It is not easy to see how altered pituitary reserves could also account for 

 the occurrence of twin ovulations. It might be that the normal extent of 

 stimulation of follicle growth is limited by estrogen, and that heavy and 

 prolonged estrogen treatment desensitized the regulating mechanism. 



