Effect of hCG concentration on embryo recovery rate in a commercial equine embryo transfer program in Brazil

Abstract

Injections were administered intramuscularly. Animals were split into five groups (n 1⁄4 25). G1: Acyclic recipients showing endometrial edema two days after treatment with 5.0 mg of estradiol benzoate (Estrogin , Farmavet, Sao Paulo, Brazil) were injected with 5.0 mL of P4LA300. G2: Cyclic mares showing one 35mm follicle and endometrial edema were treated with 2,000IU of hCG (Vetecor , Hertape Calier, Brazil) and 5.0 mL of P4LA300. Progesterone injections were discontinued at ET if an ovulation was detected. G3: Estrous recipients showing 25 mm follicles and endometrial edema were treated with 5.0 mL of P4LA300. G4: Diestrous recipients five to fourteen days post-ovulation, showing no endometrial edema and a visible corpus luteum were simultaneously treated with 5.0 mg of estradiol benzoate and dinoprost tromethamine (Lutalyse , Pfizer, Sao Paulo, Brazil). If considerable endometrial edema was detected two days after treatment, 5.0 mL of P4LA300 were administered. G5: Cyclic recipients whose ovulations were induced with 2.000 IU of hCG, serving as control. Progesterone-treated recipients received 5.0 mL of P4LA300 at ET, and, upon pregnancy diagnosis, were injected at fourteen-day intervals with 10.0 mL, until 120 days. Pregnancy at 15 days and loss rates at 120 days were statistically evaluated through Fisher's exact tests (P 0.05), respectively, 76.0% (19/25) and 10.5% (2/19) (G1); 68.0% (17/ 25) and 5.9% (1/17) (G2); 80.0% (20/25) and 10.0% (2/20) (G3); 60.9% (14/23) and 0% (0/14) (G4) and 60.0% (15/25) and 13.3% (2/15) (G5). In G2, 72.0% (18/25) showed a corpus luteum at ET, with a 72.2% (13/18) of pregnancy rate. Regardless of their estrous cycle phase or ovarian activity, recipients with either natural or pharmacologically induced endometrial edema, submitted to ET four days after treatment with long-acting progesterone, showed satisfactory pregnancy and embryo loss rates, allowing simple and effortless synchronization between donor and recipients.