DEVELOPMENT OF BOVINE EMBRYOS IN A CELL-FREE CULTURE-MEDIUM - EFFECTSOF TYPE OF SERUM, TIMING OF ITS INCLUSION AND HEAT INACTIVATION

Bovine embryos, derived from in vitro matured (IVM)/in vitro fertilize d (IVF) ova, were used to investigate the effects of timing of serum i nclusion in the culture medium and different types of blood sera and h eat inactivation of the serum on embryo development. In Experiment 1, oocytes at 18 h post insemination were allocated to 1 of the following 4 treatments: 1) TCM-199 + 0.1 mg/ml polyvinylalcohol (PVA), 2) TCM-1 99 supplemented with 10% bovine calf serum (BCS), 3) PVA medium follow ed by BCS medium at 47 h, or 4) PVA medium followed by BCS medium at 8 2 h. Supplementation with BCS at 18 h post insemination suppressed (P< 0.05) development of morulae/blastocysts (17.6%) when compared with PV A (30.5%) or with serum supplementation at 47 or 82 h post inseminatio n (32.4 and 27.6%, respectively). However, inclusion of BCS at 18, 47 or 82 h post insemination produced more blastocysts (16.8, 29.3 and 22 .1%, respectively; P<0.05) than medium + PVA(8.8%). In Experiment 2, o va were cultured from 18 h to 42 h post insemination in PVA-medium, th en greater than or equal to 2-cell embryos were transferred into serum -supplemented medium for another 168 h. Fetal bovine serum (FBS) + hea t-inactivation (56 degrees C for 30 min, = heated FBS) suppressed moru la/blastocyst development compared with medium + PVA, medium + BCS or medium + heated BCS (P<0.05). Bovine calf serum was superior to FBS in supporting blastocyst development (35.1 and 15.2%, respectively), but there was no difference between BCS and heated BCS. However, heated F BS increased the proportion of blastocysts/greater than or equal to 8- cell embryos compared with that of FBS (51.0 and 31.4%, respectively; P<0.05). These results indicate that the type of serum supplementation and the timing of its inclusion in the culture medium markedly affect bovine embryo development in vitro, and that heat inactivation of ser um with high embryotrophic properties is not necessary.