96 THE EFFECT OF CHEMICAL DELIPIDATION ON CRYOPRESERVABILITY OF CAT EMBRYOS

Abstract

Embryo cryopreservation is a desired technique for long-term preservation of embryos. However, the success rate of cryopreserved in vitro produced cat embryos is currently poor. Until recently, the mechanism underlying the cause of cryoinjury that occurs during cooling and cryopreservation is not well understood. This study aimed to examine the effect of chemical delipidation (forskolin) before cryopreservation of 4- to 8-cell cat embryos on post-thaw embryo survival and in vitro developmental capability. A total of 333 cumulus oocyte complexes (COCs) were matured and fertilized in vitro. At 24 h post-IVF, the presumptive embryos were randomly assigned into one of the following groups: 1) non-frozen control (n = 63); 2) forskolin treatment without freezing (n = 52); 3) freezing without forskolin (n = 77); and 4) freezing after forskolin treatment (n = 89). The embryos were cryopreserved using a programmable controlled-rate freezer. After freezing and thawing, the embryos were subsequently cultured in vitro for a further 6 days. The development competence was assessed by morula and blastocyst rates on Days 5 and 8 of their development, respectively. Percentages of cleaved embryos on Day 2 (IVF = Day 0) did not significantly differ among groups, indicating that there was no adverse effect of forskolin on cleavage rates. Furthermore, blastocyst formation rates of cat embryos treated with forskolin (53.5 ± 3.1) did not significantly differ when compared with non-treated controls (54 ± 9.3). Forskolin-treated embryos survived after cryopreservation at a higher rate than non-forskolin treatment, in terms of survival (93.1 ± 2.6 v. 88.2 ± 1.4), morula (56.9 ± 7.6 v. 40.8 ± 5.7), and blastocyst formation (47.6 ± 6.4 v. 35.6 ± 3.6) rates. It is concluded that partial delipidation of cat embryos before cryopreservation improves the cryopreservability of cat embryos. This study demonstrates that intracellular lipid has an impact on cryopreservability of cat embryos. Further study is required to examine in utero development of these delipidated embryos after embryo transfer.