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Effect of Age of Equine Embryos and Method of Transfer on Pregnancy Rate¹

Colorado State University, Fort Collins 80523

Abstract

A 2 x 2 cross-classified experiment was conducted to investigate the effect of age of equine embryo (7 vs 8 d postovulation) and method of transfer (surgical vs nonsurgical) on pregnancy rates at 50 d of gestation. Embryos were recovered 7 or 8 d postovulation using a Foley catheter and 3 liters of modified Dulbecco's phosphate-buffered saline (PBS). Upon identification, the embryos were placed in millipore-filtered PBS containing 20% heat- inactivated steer serum and maintained at room temperature until transferred. At the time of recovery, embryos were randomly assigned to be transferred either nonsurgically using a sterile insemination pipette or surgically via a flank incision. For nonsurgical transfer, the embryo was deposited into the uterine body; whereas, in surgical transfer, the embryo was placed in the uterine horn ipsilateral to the corpus luteum. Recovery rates for embryos collected on d 7 (75.5%) or 8 (81.9%) were similar (P>.05). Age of embryo did not affect (P>.05) pregnancy rate. At 50 d, pregnancy rates were 60 and 57% for mares receiving d 7 or 8 embryos. However, more (P<.05) pregnancies were obtained after transfer of embryos surgically (72%) than nonsurgically (45%). More (P<.05) pregnancies were obtained after transfer of d 8 embryos surgically (75%) compared with nonsurgically (40%). Within method of transfer, pregnancy rates were similar (P<.05) for surgical transfer of d 7 and 8 embryos (69 and 75%), but tended (P<.25) to be higher for nonsurgical transfer of d 7 embryos (50%) compared with d 8 embryos (40%). Other factors that affected pregnancy rates after nonsurgical transfer were size of embryo, synchrony of recipients and time of year.

¹ Portions of this research were funded by Colorado State Univ. Exp. Sta. The assistance of Drs. Voss and Shideler as well as many graduate students was gratefully appreciated.

² Present address: Lasma Arabians, LaGrange, KY 40031.

³ Animal Reproduction Laboratory, Colorado State Univ., Fort Collins, CO 30523.