Cryotolerance of in vitro matured and vitrified bovine oocytes supplemented with L-carnitine and niacin

Abstract

The study was designed to compare the cryotolerance of in vitro matured bovine oocytes, supplemented with L- carnitine and niacin in maturation media, vitrified using cryoloop technique. Bovine ovaries were collected from the slaughterhouse and cumulus-oocyte complexes (COCs) were retrieved by follicular aspiration. Culture quality COCs were selected and randomly allocated to three different experimental groups. Group I oocytes (control), were subjected to in vitro maturation (IVM) in basic maturation media, while Group II and III oocytes (experimental groups) were matured in media supplemented with L- carnitine (0.6 mg/mL) and niacin (400 μM/mL), respectively. The mean per cent of cumulus cell expansion was 80.92 ±0.02, 79.18 ± 0.03 and 87.95 ±0.02 for Group I, II and III, respectively. A significantly high (p < 0.05) cumulus cell expansion could be observed in niacin treated group than L- carnitine, whereas a difference close to being statistically significant (p = 0.057) was noticed between niacin treated and control groups. The matured oocytes were subjected to cryoloopvitrification using dimethylsulfoxide (15%), ethylene glycol (15%) and sucrose (0.05M) as cryoprotectants. The mean survival rate observed in the study was 67.26 ± 0.05, 76.34 ± 0.05 and 79.68 ± 0.03 per cent for Group I, II and III, respectively. Shrinkage of cytoplasm was the most common type of cryodamage observed in all the three groups followed by cracked zona pellucida, abnormal shape and increased peri vitelline space. The survived oocytes were subjected to in vitro fertilisation with no significant difference between the groups in fertilisation rate. The present study revealed the beneficiary effect of supplementing niacin over L- carnitine in maturation media as it improved the maturation and survival rates of bovine oocytes.