Effect of eCG and GnRH on induction of ovarian activity and conception rate in post-partum ewes

ABSTRACT

Eighteen lactating Baladi ewes were divided into four groups. Group 1 [five ewes] received progesterone releasing intravaginal sponge containing 60 mg medroxy progesterone acetate [MAP]. Group 2 [five ewes] received a home made progesterone releasing intravaginal sponge containing 500 mg progesterone. Group 3 [four ewes] as in group 1 plus 750 IU equine chorionic gonadotropin [eCG] at sponge withdrawal. Group 4 [four ewes] was treated as in group 3 plus 100 mug GnRH analogue during estrus. In all groups, sponge remained in place for 12 days. Blood samples were collected before treatment, during estrus and 7, 14, 21 and 28 days post estrus. Progesterone levels were determined using RIA. The analysis of data showed that 60, 0, 100 and 100% of ewes in the 4 groups responded to the treatment after 72.00 +/- 0.00, 54.00 +/- 12.00 and 40.50 +/- 9.00 hr for groups 1, 3 and 4, respectively. Duration of estrus averaged 21.60 +/- 5.37, 16.50 +/- 5.74 and 15.00 +/- 6.00 hours for groups 1, 3 and 4, respectively. One ewe had conceived in groups 1, 3 and 4. Progesterone levels were higher in the responding than in non responding animals, and in pregnant than in non-pregnant ewes. In conclusion, treatment with 500 mg natural progesterone failed to induce estrus in postpartum ewes, while, eCG increase the incidence of estrus and neither GnRH nor eCG could improve ewe fertility during postpartum period