| Abstrakt: |
The climatic conditions always have been the major factor for success of livestock exploration. Economic losses and operating costs in the industry attributed to heat stress are large, mainly due to the decrease in productive performance, increased mortality and decreased reproductive efficiency. There are indications that heat stress affects the physiological responses, damaging the ovarian dynamics, quality and oocyte competence of females. The aim of this study was to evaluate the effect of 2°C increase in animal temperature during the maturation, fecundation and development of bovine embryos ‘in vitro’ fertilized. COCs were obtained by follicular puncture from slaughterhouse ovaries and after identification, were divided into six groups totaling two experiments, being, control 1 (GC1) and exposed 1 (GE1) for the experiment I, and control 2 (GC2), exposed 2A (GE2A) exposed 2B (GE2B) and exposed 2C (GE2C ) for experiment II. The oocytes of the group GC1 (n=316), GC2 (n=447) and GE2C (n=297) were cultured at 38°C and the oocytes of group GE1 (n=365), GE2A (n=337) and GE2B (n=321) cultured at 40°C during the maturation period (24 hours) with 5% CO2 and 95% humidity. After the maturation period, oocytes of group GC1 and GE1 were evaluated for their morphology in optical microscope and, after removal of cumulus cells evaluated the maturation rate by the presence of polar body. In experiment II, after the maturation period, oocytes of group GC2, GE2A, GE2B e GE2C were fecundated with semen treated by Percoll discontinuous gradient. The oocytes of group GC2 and GE2C were cultured at 38°C, and the group GE2A and GE2B were cultured at 40°C throughout the period of fecundation (IVF) (18-20h). On the second day, after the FIV, the control group 2 (GC2) remained at 38°C, and the group GE2A at 40°C but, the group GE2B was cultured at 40°C and group GE2C at 38°C during embryonic development. The embryos were evaluated for cleavage rate, morula and blastocyst by means of optical microscopy. In control group 1 (GC1), the oocytes showed uniform expansion of cumulus cells, classified as moderate to high, with brown color and uniform appearance of the ooplasm, with a maturation rate of 69.62% (220/316). In the oocytes exposed to 40°C (GE1), we observed a decrease in the expansion of cumulus cells, and the same showed rounded appearance and retraction of the ooplasm with dark coloration, verifying a maturation rate of 49.04% (179/365). In the control group 2 (GC2), after the ‘in vitro’ fertilization period, the rates of cleavage, morula and blastocyst were 68.23% (305/447), 50.16% (153/305) and 43.28 % (132/305), respectively. For the group GE2A, did not observe the formation of zygotes (0/337). The group GE2B showed 31.46% (101/321) and 35.64% (36/101) of cleavage rate and morula respectively, without formation of blastocyst (0.0%), and in group GE2C, the cleavage rate was 3.7% (11/297), however, didn't observed the formation of morula and blastocysts (0.0%). For the statistical analysis of observed data, we used the x 2test (p>0.05) where it was found significance in both experiments. These data suggest that in all stages of exposure to heat stress, the embryos and the gametics cells, are susceptible, occurring decrease in embryonic development, ie, the increase of temperature influences negatively in the animal reproduction, causing a fall in oocyte maturation, fecundation and embryonic development.Support from Cnpq and FAPESP. |
