Proceedings of the 5th International Symposium on EQUINE ...

Havemeyer Foundation Monograph Series No. 3FACTORS AFFECTING PREGNANCY RATES ANDEARLY EMBRYONIC DEATH AFTER EQUINE EMBRYOTRANSFERE. M. Carnevale, R. J. Ramirez, E. L. Squires, M. A. Alvarenga and P. M. McCueAnimal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, Colorado80523, USASuccess <strong>of</strong> a commercial embryo transferprogram is dependent upon identifying factorsthat affect pregnancy and embryonic death.Previous studies have examined <strong>the</strong> effect <strong>of</strong>method <strong>of</strong> transfer, technician, size, age <strong>of</strong>embryo, embryo morphology, season <strong>of</strong> <strong>the</strong> year,synchrony between donor and recipient, andculture and storage <strong>of</strong> embryos (Squires et al.1982; Iuliano and Squires 1985; McKinnon andSquires 1988; Cook et al. 1989; Carney et al.1991; Squires et al. 1992; Squires and Seidel1995; Fluery and Alvarenga 1999; McCue et al.1999; Squires et al. 1999). This is a retrospectivestudy involving 638 embryos transferred intorecipients at Colorado State University EquineReproduction Laboratory during 1996, 1997 and1998. The objective <strong>of</strong> this retrospective studywas to determine which factors (recipient orembryo) had significant effects on pregnancy andembryonic loss rates. Donor mares were ei<strong>the</strong>rmares housed at Colorado State University orthose housed at various breeding farmsthroughout <strong>the</strong> United States. Embryos werecollected 7 or 8 days after ovulation ei<strong>the</strong>r atCSU or collected on <strong>the</strong> farm, cooled andtransported within 24 h to Colorado StateUniversity. Recipients were light horse maresbetween 2 and 18 years <strong>of</strong> age and 400 to 600 kg.Cycling recipients were examined by palpationand ultrasound at regular intervals and dailyduring oestrus. Reproductive tracts wereexamined for <strong>the</strong> detection <strong>of</strong> follicular activity,day <strong>of</strong> ovulation, presence <strong>of</strong> <strong>the</strong> corpus luteum,uterine oedema, and fluid in <strong>the</strong> uterine lumen.Recipients were classified as ‘acceptable’ if awell-defined corpus luteum and a good toexcellent cervical and uterine tone were present.Recipients were classified as marginallyacceptable if <strong>the</strong>y had a small or poorly imagedcorpus luteum and/or poor to fair cervical anduterine tone. Embryos were measured and gradedbased on morphology ((McKinnon and Squires1988). Embryos shipped from ano<strong>the</strong>r locationfor subsequent transfer were placed in a plasticculture tube containing transport medium (Ham’sF10 with 10% fetal calf serum plus 1%penicillin/streptomycin), which was gassed with5% CO 2 , 5% O 2 and 90% N 2 . Embryo werepackaged in Equitainers as previously describedand transported via a commercial airline or parceldelivery service (Squires et al. 1992). Transporttime varied from 6 to 32 h. Pregnancy rates onDay 50 were significantly higher for recipientsthat had excellent to good uterine tone and weregraded as acceptable recipients vs recipients thathad fair to poor uterine tone and gradedmarginally acceptable (60% vs 45%). Embryonicfactors that affected pregnancy rates significantlywere morphology grade, diameter and stage <strong>of</strong>development. Embryos 100 to 200 µm resulted inlower pregnancy rates. As expected, thoseembryos given a quality grade <strong>of</strong> 1 (excellent)resulted in higher pregnancy rates that thosegraded 2, 3 or 4. Fewer (P