PRODUCTION, FREEZING AND TRANSFER OF BOVINE IVF EMBRYOS AND SUBSEQUENT CALVING RESULTS

Ultrasound-guided oocyte aspirations were performed repeatedly, on a w eekly basis, on 155 different cows. An average of 4.9 oocytes with 4.1 classified as usable were collected. Following in vitro maturation (I VM), fertilization (IVF) and culture (IVC), a few Day 7 morulae, and a ll Day 7 and most Day 8 blastocysts were either transferred or frozen. The transfer of 2268 fresh IVF embryos resulted in 1220 pregnancies ( 53.8%). embryos resulted in a higher (56%) pregnancy rate than did Day 8 (43%) or Day 9 (41%). in addition, of embryos classified as grade 1 on either Day 7 or 8 resulted in a higher pregnancy rate than did gra de 2 embryos Although there was no difference in pregnancy rate, embry os resulting from co-culture with Buffalo Rat Liver Cells in Menezo's B2 medium developed faster than embryos co-cultured with TCM 199 faste r culture medium. Pregnancy rate following transfer of IVF blastocysts frozen on Day 7 was 42% and dropped to 20% for blastocysts frozen on Day 8. Pregnancy rate was not Influenced when synchrony between the IV F embryo and recipient was within +/-36 h. The sex ratio of the result ing calves did not deviate from normal but there was a higher than nor mal incidence of early abortions and dystocias. There appeared to be s ome increase in calf birth weights.