PREGNANCIES, CALVES AND CALF VIABILITY AFTER TRANSFER OF IN-VITRO PRODUCED BOVINE EMBRYOS

Pregnancy, parturition and calf survival following the transfer of emb ryos produced in vitro were monitored. A total of 44 blastocysts was t ransferred in pairs to 1 uterine horn ipsilateral to the corpus luteum (CL) of 22 synchronized heifers. At Day 42 of development 14 recipien ts (64%) were pregnant; the calving rate was also 64%. The twinning ra te was 9/14 at Day 42 and 7/14 at birth, for an overall fetal mortalit y rate of 9%. The average gestation length was 281 and 275 d for singl e and twin pregnancies, respectively. Blood samples from recipients we re collected for determination of bovine pregnancy associated glycopro tein (bPAG) from 2 wk after transfer and throughout the pregnancy. Dur ing the first trimester of pregnancy, the bPAG concentration was signi ficantly higher in twin than in single bearing heifers, and the perina tal increase in bPAG was correlated positively with the total weight o f the fetus(es). The percentage of male calves was 43%. The birth weig ht of twin individuals was 25+/-1 kg, which was 78% of the birthweight of the singletons (32+/-2 kg). One singleton calf was oversized, weig hing 58 kg (80% more than the median weight of the other singletons). Stillbirths occurred in 21% of the twins, but in none of the singleton s. Calf mortality during the first 14 d was higher for twins (4/11) th an for singletons (1/7) due to infections and cerebellar hypoplasia. K aryotyping the calves detected no cytogenetically recognizable abnorma lities. All calves were negative for BVD virus and IBR antibodies. The results of this study showed that although the incidence of fetal los s was low, there was an unacceptable high perinatal mortality of the c arves. Thus it is likely that the blood supply through the placenta of animals pregnant with twins was impaired or it is possible that these fetuses and calves had increased stress susceptibility caused by the in vitro conditions. Furthermore, the birth of 1 oversized calf, 2 cal ves with cerebellar hypoplasia and 5 calves succumbing to infections s eems to indicate that a proportion of in vitro produced calves may suf fer from factors inherent in the in vitro production system.