110 THE USE OF FORSKOLIN AND ITS EFFECT ON IN VITRO-PRODUCED BRAHMAN-SIRED EMBRYOS SUBMITTED TO SLOW COOL FREEZING OR VITRIFICATION

Abstract

The objective of this study was to further test the lipolytic effect of 10 μM forskolin on developmental differences between bovine in vitro produced (IVP) embryos submitted to slow cool (SC) freezing or vitrification (VT). Previously reported (phase I) IVP embryo hatching rates for control embryos (62%) were no different than 10 μM forskolin (67%; Pryoretal et al. 2009 Reprod. Fertil. Dev. 21, 163). For phase II: on Day 6 post-fertilization (IVF = Day 0), 207 Brahman-sired viable embryos were evenly divided and cultured for 24 h in G2.5 medium (Vitrolife, Englewood, CO, USA) with or devoid of 10 μL forskolin (Sigma, St. Louis, MO, USA). On Day 7, compact morula (CM, n = 31), blastocyst (BL, n = 76), and expanded BL (XBL, n = 100) were washed in Vigro Holding Plus medium (Bioniche, Pullman, WA, USA) and randomly allocated to 4 treatment groups; control SC (CSC; no treatment, n = 52), 10 μM forskolin SC (FSC; n = 55), control VT (CVT; n = 49), and 10 μM forskolin VT (FVT; n = 51). All embryos were packaged in sterile 0.25-mL plastic straws. The SC embryos were submitted to Vigro Ethylene Glycol Freeze Plus medium (Bioniche) for 5 min before freezing at 0.5°C/min from -6°C to -32°C and plunging in LN2. Embryos were vitrified using a bovine VT kit (Bioniche): VS1, 3 min; VS2, 45 s in 15 μL; diluent, in straw with VS2 separated by air columns, vitrified in LN₂ vapor 1 cm from liquid for 1 to 15 min before plunging. The SC embryos were air thawed 5 s and placed in 30°C H₂O bath for 10 s. The VT straws were air warmed 10 s and then in 35°C H₂O for 20 s prior to shaking them down to mix columns. All embryos were cultured in G2.5 for 24-h survival and 48-h hatching rates. All percentage data were transformed using arcsin square root function prior to analysis, and means were compared for statistical significance using Student’s t. For mean survival rates, FSC was different than CSC but showed no difference between FVT and CVT (81.7 ± 0.09, 42.6 ± 0.09, 59.4 ± 0.09, 49.0 ± 0.10, respectively (P < 0.01). There were no statistical differences for hatching rates for combined embryo stages (58.2 ± 0.10, 37.8 ± 0.10, 34.4 ± 0.10, 28.1 ± 0.11 for FSC, FVT, CSC, and CVT, respectively; P > 0.07). However, when comparing hatching rates of only the blastocyst stage embryos (n = 176), FSC was superior to CSC and CVT but not different than FVT (74.8 ± 0.11, 29.5 ± 0.11, 29.1 ± 0.11, 48.5 ± 0.11, respectively; P < 0.01). In conclusion, FSC yielded significantly higher survival and blastocyst hatching rates than CSC, but there were no differences between CVT and FVT for survival and FVT for blastocyst hatching rates. These results indicate that the addition of 10 μM forskolin to culture 24 h prior to freezing 7 d IVP Brahman-sired embryos can increase survival and blastocyst hatching rates.

The authors acknowledge support from the American Brahman Breeders Association.