97 Effect of season and oxygen tension on developmental competence of bovine oocytes
A. Rodríguez A , I. Arburuas A , V. de Brun B , N. Rodríguez-Osorio C , C. Viñoles D and F. Báez AA Instituto Superior de la Carne, Centro Universitario Regional Noreste, Universidad de la República, Tacuarembó, Uruguay
B Laboratorio de Endocrinología y Metabolismo Animal, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay
C Departamento de Ciencias Biológicas, Unidad de Genómica y Bioinformática, Centro Universitario Regional Litoral Norte, Universidad de la República, Salto, Uruguay
D Centro de Salud Reproductiva de Rumiantes en Sistemas Agroforestales, Centro Universitario Regional Noreste, Universidad de la República, Cerro Largo, Uruguay
Reproduction, Fertility and Development 35(2) 175-175 https://doi.org/10.1071/RDv35n2Ab97
Published: 5 December 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
In temperate regions, during summer, beef cows grazing native pastures can be exposed to acute heat stress, which may affect the quality and developmental competence of cumulus-oocyte complexes (COCs). For bovine in vitro oocyte maturation (IVM) and fertilisation (IVF), it is common to use ∼20% oxygen tension, which is considerably higher than the one found in the cow’s follicular fluid (5 ± 2%) and oviduct (∼2%). This supraphysiological oxygen tension can cause an increase in the production of reactive oxygen species, implicated in many types of cell injuries such as apoptosis. Since a hyperoxic environment could exacerbate the magnitude of damages experimented by bovine oocytes under elevated temperature, using low oxygen tension could be an alternative to minimise the adverse effects of heat stress on oocyte competence. The objective of this study was to assess the effect of seasonality on the developmental capacity of bovine COCs after IVM-IVF at 5% O2 or 20% O2. In North Uruguay, we collected cow ovaries from a slaughterhouse monthly during summer (January to March 2022) and winter (June and July 2022) and calculated the temperature-humidity index (THI) throughout the time of the study. After IVM-IVF, presumptive zygotes (n = 163–195 per group) were cultured at 5% O2, 5% CO2 at 38.5°C for eight days in synthetic oviducal fluid medium. Expanded blastocysts from each group were stained with terminal deoxynucleotidyl transferase fluorescein-dUTP nick-end labelling (TUNEL) to determine the number of blastomeres and apoptotic index. Cleavage and blastocyst rates, total cell number, and apoptotic index in expanded blastocysts (n = 8–11 per group) obtained in winter and summer under both oxygen tensions were analysed by a two-factor ANOVA with Tukey’s test. Average summer THI was 73, indicating an alert level for cows under conditions of acute heat stress. The results showed that season and oxygen tension during IVM-IVF significantly affected cleavage, blastocyst rates, and quality of embryos. Oocytes collected in winter using 5% O2 fielded the best results, while oocytes collected in summer using 20% O2 during IVM-IFV fielded the worst results (Table 1). These findings suggest that heat stress and oxygen tension have an accumulative negative effect on the developmental competence of bovine oocytes.
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