Embryo transfer into anestrous recipient mares prepared using clomiphene citrate and short-acting progesterone

Embryo transfer (ET) is an important technology for genetic improvement programs in the equine industry. Many protocols have been used for preparation of recipients. This study evaluates a new protocol for preparation of acyclic embryo recipient mares using clomiphene citrate (CC) and short-acting oral progesterone (Altrenogest). Seventy-two native breed recipient mares were divided into 2 groups. Group 1(G1) included 60 non-cyclic mares with follicular structures ≤ 15 mm in diameter that received CC and Altrenogest. Group 2 (G2) included 12 cyclic recipient mares that served as a control group. G1 mares were treated with oral CC at a dose of 250 mg for 4 days followed by oral administration of Altrenogest for 6 days. Ultrasonography was carried out for evaluation of uterine echotexture response to hormonal treatment, and pregnancy diagnosis post ET. Serum estradiol and progesterone concentrations were also assessed. All data were statistically analyzed. The results revealed that the serum progesterone concentrations in G1 were higher than G2 (P < 0.001). There was no difference in the estradiol concentrations between both groups during diestrus phase (P > 0.05). The pregnancy rate was higher in G1 (83.3 %) than G 2 (66.6 %). In conclusion, using oral CC and Altrenogest, as a new protocol, was effective for preparation of acyclic recipient mares in this study.