Effect of heat stress on the maturation, fertilization and development rates of in vitro produced bovine embryos

Mayra Fernanda Alves, Roseli Fernandes Gonçalves, Danielle Labadessa Pavão, Eduardo Gimenes Palazzi, Flavio Souza, Roberta Kelly Ribeiro de Queiróz, Magali D’ Angelo, Marcos Antônio de Achilles

1Cell Biology Laboratory, Research and Development Center for Animal Health, S?o Paulo Biological Institute, S?o Paulo, Brazil.
Cell Biology Laboratory, Research and Development Center for Animal Health, S?o Paulo Biological Institute, S?o Paulo, Brazil.
Department of Animal Reproduction, College of Medicine Veterinary and Animal Science, S?o Paulo University, S?o Paulo, Brazil;.

DOI: 10.4236/ojas.2013.33026                

Abstract

Heat stress is one of the main reasons for reproductive performance decrease in cattle, resulting in severe economic losses. The aim of this study was to evaluate the effect of heat stress during maturation, fertilization and development of in vitro produced bovine embryos. Cumulus oocyte complexes (COCs) were obtained by follicular puncture from slaughterhouse ovaries and after identification, were divided into four groups: control (CG), exposed 1 (EG₁), exposed 2 (EG₂), and exposed 3 (EG₃). The oocytes of the group CG and CG₃ were cultured at 38°C and the oocytes of group EG₁ and EG₂ were cultured at 40°C during the maturation period (24 hours at 5% CO₂ in air). After the maturation period, oocytes of group CG, EG₁, EG₂, and EG₃ were fecundated with frozen thawed semen. The oocytes of CG, EG₂ and EG₃ groups were cultured at 38°C, and the group EG₁ was cultured at 40°C (18 hours at 5% CO₂ in air). After that, the CG and EG₂ groups were cultured in SOF at 38°C and the groups EG₁ and EG₃ at 40°C during embryonic development. The embryos were evaluated for cleavage, morula and blastocyst rates by optical microscopy. In control (CG) and EG₃ groups, the oocytes showed uniform expansion of cumulus cells, classified as moderate to high, with brown color and uniform appearance of the ooplasm. In the oocytes exposed to 40°C (EG₁ and EG₂) we observed a decrease in the expansion of cumulus cells, and the same showed rounded appearance and retraction of the ooplasm with dark coloration. The control group (CG) had 68.23% ± 2% of cleavage, 50.16% ± 2% morulas, and 43.28% ± 1% blastocysts. Whereas the EG₂ had 31.46% ± 2% cleavage, 35.64% ± 2% morula, and no blastocysts development. The EG₃ had 3.7% ± 2% cleavage, and no embryo production. These data suggest that in all stages of exposure to heat stress, the embryos and the gametes are susceptible, leading to a decrease in embryonic development.

Keywords

Bovine; Embryo; Heat Stress; in vitro Fertilization

Conflicts of Interest

The authors declare no conflicts of interest.

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