In commercial equine embryo transfer programs, the cost of recipient mares represents one of the major economical items that increases the final cost of the pregnancies (Douglas 1985; Losinno and Alvarenga 2006). Due to the risks to newborn foal, it is uncommon to use foaling recipients in the large equine embryo transfer programs in Argentina. The objective of this study was to evaluate pregnancy and early embryonic loss rates between foaling and non-foaling recipients in a commercial embryo transfer program. A total of 173 embryos were collected from Arabian donor mares during 3 consecutive breeding seasons, 2006-2009. Donor mare’s ages ranged from 2 to 22 years, and donors were inseminated with either fresh or frozen semen from 8 stallions 2-17 years old and of proved fertility. Uterine flushing was performed on Day 8 to 9 post-ovulation by standard techniques (Douglas 1985) and recovered embryos were transferred nonsurgically. Recipient mares 3-12 years old were selected clinically by rectal palpation and ultrasound. All embryos were transferred to synchronized recipient mares (-1 to +1 according to donor’s ovulation day) and randomly assigned to non-foaling (n = 84) or foaling (n = 89) recipient groups. For the analysis, we first considered pregnancy and early pregnancy loss rates in both groups, and second, the foaling mares were divided in 3 groups according to the days between foaling and transfer: 1) before 30 days postpartum (n = 10), 2) between 31 and 60 days postpartum (n = 30), and 3) after 61 days postpartum (n = 49). Pregnancy diagnosis was performed by ultrasonography on Days 14, 30, and 60 post-ovulation of the donor. Results were evaluated by chi-square test. No statistical differences (P > 0.05) were observed in pregnancy rates between non-foaling and foaling recipients (76.2% and 80.9%, respectively) and in post-foaling groups (80% for recipients transferred before 30 days postpartum, 73.3% for recipients transferred between 31 to 60 days postpartum, and 85.7% for recipients transferred after 61 days postpartum). No statistical differences (P > 0.05) were found in pregnancy loss rates between recipients transferred before 30 and after 61 days postpartum (25% v. 4.8%, respectively) and between recipients transferred before 30 days postpartum and the non-foaling group (25% v. 10.9%, respectively). Pregnancy loss rates for recipients transferred after 31 and 61 days postpartum (9.1% and 4.8%, respectively) were not significantly different with the non-foaling group, and both are within previously reported values. Our results show that postpartum recipients can be used 30 days after normal foaling in a commercial embryo transfer program with similar pregnancy and early pregnancy loss rates and can be a valuable tool maximizing the use of the recipient mares during consecutive breeding seasons.
CAUSES OF EARLY PREGNANCY LOSS IN FROZEN-THAWED EMBRYO TRANSFER CYCLES
