TRANSFER OF BOVINE EMBRYOS PRODUCED IN-VIVO OR IN-VITRO - SURVIVAL AND FETAL DEVELOPMENT

The objectives of the present experiment were to compare survival afte r transfer of bovine embryos produced in vivo with those produced in v itro and to examine the physical characteristics of fetuses produced f rom these transfers. Embryos produced in vivo (Holstein X Angus) were recovered from uterine flushings of superovulated heifers 7 days after first artificial insemination, and embryos produced in vitro (Holstei n X beef breeds) were collected 7 days after insemination. Embryos wer e paired by source (in vivo, in vitro), stage (compact morula, blastoc yst), and quality grade (excellent = 1, good = 2), and transferred non surgically to recipient heifers on Day 7 (+/- 1 day) of the estrous cy cle. Pregnancy status was monitored by determination of serum progeste rone concentrations, ultrasonography, and palpation through 7 mo of ge station, at which time fetuses were recovered. In comparison with grad e 1 embryos produced in vivo, the risk of embryonic death after transf er was similar for grade 2 embryos produced in vivo (p = 0.56) and for grade 1 embryos produced in vitro (p = 0.88). By contrast, grade 2 em bryos produced in vitro were at greater (p = 0.04) risk of embryonic d eath. Embryo loss was associated (p = 0.01) with increased serum conce ntrations of progesterone in recipients at the time of transfer. At 7 mo of gestation, fetuses from embryos produced in vitro were heavier ( p = 0.02) than fetuses from embryos produced in vivo and had skeletal measurements that were disproportionate (p less than or equal to 0.04) to body weight.