Assessment of viability of bovine oocytes using 3-(4-5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide

Abstract

The purpose of the present work was to evaluate the viability of bovine Cumulus Oocyte Complex (COC), using 3-(4-5-dimethylthiazol-2-yl)-2,5-diphenil tetrazolium bromide (MTT). The COC's were obtained by aspirating 2-5 mm follicles from the ovaries of cows at slaughter. The COCs were selected according to the characteristics of the cumulus (complete, partial or absent) and the cytoplasm of the oocytes (uniform or vacuolated).. The COCs were classified in three groups: 512 (category A= complete cumulus and uniform cytoplasm), 503 (category B= incomplete cumulus and uniform cytoplasm) and 439 (category C= uniform cytoplasm and no cumulus). The COCs were incubated with MTT solution at 37ºC, 5% CO2 nd 99% humidity during 4 hours. MTT is colorless or light yellow and penetrates in the cellular membrane, this solution changes to dark blue by the reduction of mitochondria dehydrogenises. The staining was negative when the COCs did not show changes, and light, moderate or intense when the COCs showed color changes with different intensity. The majority of COCs in categories A & B (good quality) showed color changes, meaning that the enzymatic activity increased. Twenty three percent of A & B COCs showed negative staining. Approximately 45% of COCs in C category (poor quality) showed no color change, being classified as negative. To determine the quality of the COCs it is necessary to use techniques that show functional and structural characteristics.