Estrous Cycle Synchronization In

E STRUS and ovulation in gilts have been successfully inhibited by daily injections of progesterone (Ulberg et al., 1951; Baker et al., 1954) and more recently by the inclusion of progestational compounds in the feed (Nellor, 1960; Dzuik and Baker, 1962). The successful use of orally active progestational agents to synchronize the estrous cycles of gilts without a subsequent reduction in fertility offers a practical management technique for facilitating the operation of multiple farrowing programs. The use of these orally active compounds has been found to be associated with formation of cystic ovarian follicles (Nellor et al., 1961). First et al. (1963) studied the factors affecting ovulation and follicular cyst formation in sows and gilts fed 6-methyl-17-acetoxyprogesterone. They found that dosage level of the hormone, but not frequency of feeding or energy or fiber content of the diet, affected follicular cyst formation. The purpose of the work reported was: (1) to obtain further data concerning the use of orally effective progestational compounds for estrus control in gilts, (2) to observe the influence of a period of estrogen derivative feeding just prior to the progesterone derivative feeding on estrus synchronization, and (3) to observe the effect of feeding these hormones on fertility.