CALVES BORN AFTER TRANSFER OF UNFROZEN AND FROZEN-THAWED IN-VITRO PRODUCED EMBRYOS

A total of 139 embryos produced in vitro either in coculture with oviduct cells or in medium conditioned by these cells in the presence or absence of serum were transferred either after culture (63) or after culture and freezing (76) resulting in 29 calves born (18 males, 11 females) weighting between 40 and 60 kg, after a mean gestation length of 290 days. The bull used for fertilization was of the Belgian Blue breed and his gestation length recorded in vivo is longer than the mean. The final calving yield was 21 %. The best calving rates were obtained from embryos cultured in 'serum-free' oviduct-conditioned medium 5/16 (31 %) for embryos transferred individually after culture and 4/17 (24 %) for embryos transferred after culture and freezing. Too more pregnancies are confirmed in the last group after transfer of 2 day 6 blastocysts stored for 1 year in liquid nitrogen. Serum PAG (Pregnancy Associated Glycoprotein) level was lower in the recipients receiving frozen embryos than in those receiving non frozen embryos. A field trial consisting in the transfer of 105 frozen-thawed embryos by Al veterinarians resulted in 12 pregnancies (11 %).