TITLE:
Effect of heat stress on the maturation, fertilization and development rates of in vitro produced bovine embryos
AUTHORS:
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
KEYWORDS:
Bovine; Embryo; Heat Stress; in vitro Fertilization
JOURNAL NAME:
Open Journal of Animal Sciences,
Vol.3 No.3,
July
8,
2013
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.