Influence of physiological concentrations of androgens on the developmental competence and sex ratio of in vitro produced bovine embryos.

This study was designed to determine if the addition of androgens at ovarian follicular fluid (FF) concentrations to oocyte maturation media would alter the development and sex ratio of bovine embryos. To maximize hormone bioavailability, oil was removed and glass culture dishes were used during in vitro maturation (IVM) phase; this modified system was then used in the present experiment along with the standard IVM system utilizing plastic containers and incubation under oil. Ethanol (0.2%) was the vector for steroid hormone delivery. Oocytes were incubated for 22h in the presence of two doses ("low" and "high") of androstenedione (A4) or testosterone (T); the doses were based on the concentrations of both androgens in preovulatory bovine follicles (A4: 337.5 and 562.5ng/ml; T: 22.2 and 42.6ng/ml). The results of hormone assays indicated that bioavailability of steroid hormones remained relatively constant, regardless of the IVM system used. The plasticware with the addition of T resulted in significantly higher cleavage rates (80.0±2.1%) than any other combination of treatments (plasticware×A4: 71.5±2.6%; glassware×T: 71.2±1.9%; and glassware×A4: 71.4±2.4%). The blastocyst formation rate for the plasticware×T treatment (39.7±2.5%) was significantly greater than for all other combinations (glassware×T: 28.7±2.2%; glassware×A4: 24.0±2.8%; and plasticware×A4: 19.8±3.0%) and the low dose of T (37.1±2.5%) resulted in higher (p<0.05) blastocyst formation rates than all other treatments (T high dose: 29.2±2.5%; A4 high dose: 27.1±2.9%; and A4 low dose: 20.2±3.0%). The proportion of male embryos was greater (p<0.05) in plastic than glass dishes in the low-dose A4 group (59.1±8.7% vs. 38.2±5.5%, plasticware vs. glassware, respectively) and it tended to be greater (p<0.08) in the control groups and high-dose A4 group, but not in the T groups. There was a moderate positive correlation between blastocyst formation rates across all treatment and control groups, and the percentage of male bovine embryos (r=0.38, p<0.05). In summary, specific combinations of androgen and glassware/plasticware treatments did alter early bovine embryo development and sex ratio. The addition of T to IVM media increased the cleavage and blastocyst formation rates in plasticware and may be employed to improve the efficiency of the standard in vitro embryo production systems. Androstenedione appeared to enhance whereas testosterone nullified the deviation in sex ratio (pro-femaleness) associated with the use of glass IVM dishes.