Effect of stimulation with a gonadotropin mixture onreproductive outcome in nulliparous ewes bred duringseasonal anestrus and early breeding season

Breeding replacement ewes to lamb for the first time at 1 year of age increases lifetime productivity of the ewe and overall productivity. Ewe lambs born to fall lambing systems reach the age at which they should attain puberty during spring/summer when reproductive activity is suppressed. As a consequence few ewe lambs can be successfully bred during seasonal anestrous. In this study we demonstrated that gonadotropic stimulation with a gonadotropin mixture containing 240 IU of eCG and 120 IU of hCG following progesterone pre-treatment improved reproductive outcome in fall-born ewe lambs bred during the mid-anestrous period with estrous response and pregnancy rate to the first service period comparable to that observed in adult females. Further, Progesterone pre-treatment alone was sufficient to induce fertile estrus and advance the breeding season in yearlings bred during mid- and late-anestrus.