Variations in metabolic parameters of in vitro matured porcine oocytes after vitrification-warming

As the porcine oocyte is the most sensitive to low-temperature damage, it has been difficult to cryopreserve compared to those from other domestic animals. However, at present, vitrification is used as a method for the cryopreservation of both oocytes and embryos in this species.

Our aim was to analyze alterations in metabolic parameters in vitrified-warmed in vitro matured porcine oocytes at different post-warming recuperation times. In addition, metaphase II plate recovery time analysis, in vitro fertilization, and intracytoplasmic sperm injection were carried out to evaluate oocyte recovery capacity.

Oocytes were vitrified-warmed and then incubated for 0, 3, or 21 hours post-warming to assess biochemical parameters.

Oocyte viability and morphology were not affected by vitrification-warming. Cytosolic oxidative status, active mitochondria, and reactive oxygen species levels presented changes at the different time points in control and vitrified-warmed oocytes (p < 0.05) as well as differences between both groups (p < 0.05). Nicotinamide adenine dinucleotide phosphate levels remained constant throughout different recuperation times but were significantly lower in vitrified-warmed oocytes (p < 0.05). Metaphase II plate recovery occurred mostly between 3 and 4 hours post-warming, but the percentage of metaphase II was reduced by vitrification-warming. Sperm head decondensation and pronuclear formation capacities were not modified.

In conclusion, vitrification-warming generates biochemical alterations in porcine oocytes that would be, in part, responsible for affecting their performance. Therefore, although the technique is a valid alternative for porcine oocyte cryopreservation, the protocols should be adapted to minimize those alterations.