63 VITRIFICATION OF BOVINE IN VITRO-PRODUCED AND IN VIVO EMBRYOS

Abstract

There is increasing interest in vitrification as a method of cryopreserving bovine embryos, especially previously problematic embryos such as IVP and Jersey cattle embryos, which, it has been suggested, have lower tolerance to cryopreservation because of the high lipid content of the embryo interfering with water movement out of the cells. Jersey embryos were demonstrated to have lower pregnancy rates following cryopreservation compared with Holstein embryos [Steel R et al. 2004 Reprod. Fertil. Dev. 16(Suppl. 2), 120 abst]. The first trial aimed to compare the subsequent pregnancy rate of vitrified and fresh in vitro-produced embryos. Embryos were produced by 9 Friesian cows through transvaginal recovery and in vitro production (IVP) over a 10-week period. The embryos produced during the first 6 weeks were all vitrified and warmed during the last 4-week period concurrent with the transfer of fresh embryos produced from the same donor cows at that time. Vitrification and warming were performed using a technique previously reported (Peachey B et al. 2005 Reprod. Fertil. Dev. 17, 199 abst) using the CVM method (Lindemans W et al. 2004 Reprod. Fertil. Dev. 16, 174 abst). All embryos were transferred by the same experienced technician into randomly assigned synchronized recipients of the same herd. All recipients were scanned for pregnancy 40 days after transfer. Data (Table 1) were compared by Fisher exact test and showedno significant difference (P = 0.761) between pregnancy rates of vitrified-warmed embryos and fresh embryos. This result demonstrates that vitrification is a valuable technique in cryopreservation of IVP embryos. In a second trial, pregnancy rates of in vivo-produced Jersey embryos after slow freezing and vitrification were compared. Embryos were flushed from 6 Jersey cows and randomly divided into 2 groups to be cryopreserved. The first group of 12 embryos (DT) were cryopreserved by slow freezing (0.3°C min^–1 to –35°C) in 1.5 m ethylene glycol + 0.1 m sucrose. The second group of 12 embryos (VIT) were vitrified and warmed, using the same technique as described above. All embryos were transferred on the same day, by the same experienced technician, to randomly assigned recipient cows in the same herd. The pregnancy results for VIT were 7/12 (58%) and for DT were 4/12 (33%). The data were compared by logistic regression (Genstat v. 10, VSN International, Hemel Hempstead, UK) to account for donor effect, and no significant difference (P = 0.462) was found. It is proposed that the lack of significant difference may be due to the small numbers in the trial but that the results are promising enough to warrant further use and evaluation of this technique in the cryopreservation of Jersey cattle embryos.

Table 1.  Pregnancy rates of fresh v. vitrified/warmed IVP embryos