Development of in vitro fertilized feline embryos in a modified Earle's balanced salt solution: influence of protein supplements and culture dishes on fertilization success and blastocyst formation.

The effects of protein supplements and culture dish type on in vitro fertilization (IVF) and embryo development in culture were examined in the domestic cat. In Experiment I, follicular oocytes were fertilized and cultured in either 1) modified Earle's balanced salt solution, designated MK-1, supplemented with one of the following: 10% human serum (HS), 10% FCS or 0.4% BSA, or 2) Medium 199 (M-199) supplemented with 10% FCS. Fertilization rates were lower (P < 0.01) in MK-1 + BSA (74.4%), MK-1 + FCS (56.1%), and M-199 + FCS (51.4%) than in MK-1 + HS (94.7%). A greater (P < 0.01) percentage of blastocysts was obtained in MK-1 + HS (50.0%) than in other treatment groups (range, 4.3-17.2%). In Experiment II, the effect of dish type (tissue culture dish, TCD, versus suspension culture dish, SCD) on embryo development was evaluated in MK-1 supplemented with either HS or BSA. Significantly higher proportions of IVF-derived embryos developed to blastocysts at 120 and 144 hr post-insemination, respectively, when cultured in HS/SCD (47.2 and 71.7%) than in BSA/SCD (11.4 and 27.3%) or BSA/TCD (10.4 and 25.0%). At 120 hr post-insemination, there was a lower (P < 0.01) percentage of blastocysts in HS/TCD (22.2%) than in HS/SCD. In Experiment III, six embryos per cat were transferred to the uterine horns of 17 recipients at 144 hr after hCG treatment. Five of 7 recipients which received late morulae cultured in MK-1 + BSA (SCD) for 120 hr became pregnant (71.4%). Eight of 10 recipients which received early blastocysts cultured in MK-1 + HS (SCD) for 120 hr became pregnant (80.0%). We conclude that MK-1 containing HS is highly beneficial for overcoming the in vitro developmental block of IVF-derived feline embryos and increasing the success rate of IVF/ET.