Antioxidant supplementation effects on in vitro maturation and fertilization of dromedary camel oocytes

The current investigation was conducted to evaluate the effects of antioxidant addition (ascorbic acid, cysteine, and a combination of both) to the in vitro maturation medium of dromedary camel oocytes on maturation rate, as well as to investigate maturation medium antioxidant supplementation on in vitro fertilization of oocytes. The oocytes were retrieved by slicing ovaries collected from a local slaughterhouse. Recovered oocytes were examined before and after in vitro maturation (IVM) culture for grading, investigating cytoplasmic and nuclear maturation. Only good-quality oocytes (with more than one layer of cumulus cells and homogeneous dark cytoplasm) were selected (n=656) and allocated into four groups, namely: the control group (G1) was cultured in an IVM medium free of antioxidant; Group 2 (G2) was supplemented with 100 µg/ml ascorbic acid; Group 3 (G3) was supplemented with 6.9 µM cysteine; and the fourth group (G4) was supplemented with a mix of 100 µg/ml ascorbic acid and 6.9 µM cysteine. All groups were incubated at 38.5 ºC, 5% CO2 and 95% humidity for 40 hours. In the in vitro fertilization experiment, cumulus oocytes complexes (COCs) were inseminated with frozen-thawed semen (3x106 spermatozoa/ml) then cultured in the fert-TALP medium at 38.5 ºC, 5% CO2 and 95% humidity for 18 hours. The mean recovery rate was 8.83 oocytes per ovary. After IVM, the maturation rate due to expansion in cysteine (89.62%) was significantly higher than the control group (78.98%), the ascorbic acid group (76.04%) and the mix group (72.64%). However, according to the polar body extrusion percentage, the results revealed that the maturation medium treated with ascorbic acid (29.17%) was significantly higher than the cysteine group (20.75%), the G4 mix group (17.83%) and the control group (10.45%). The results of the fertilization trial showed that there was no significant difference between the ascorbic acid group (9.72%) and the control group (5.97%). In conclusion, the treatment of in vitro maturation medium with 6.9 µM cysteine improved cumulus cells expansion, while ascorbic acid supplementation (100 µg/ml) improved the first polar body extrusion. However, the combination of both had a negative effect on both expansion and polar body