REVIEW PAPER
The application of in vitro cattle embryo production system to study the influence of elevated temperature on oocyte maturation, fertilization and early embryonic development

Higher air temperature in summer causes a significant reduction in fertility in cattle. Increase in female body temperature

during the period of reproduction by only 2°C, also known as hyperthermia, leads to disturbances in the

functioning of the female reproductive system, oocytes maturation, fertilization and embryos development.

Particularly sensitive to high temperatures are embryos in the first and second day after fertilization (thermosensitive),

but just at third till fifth day after fertilization their resistance to thermal stress significantly increases.

Morula-stage and blastocyst-stage bovine embryos are insensitive to elevated temperatures (thermoresistant).

Most probably this is due to the increasing number of cells within the embryo and the capacity to activate defense

mechanisms based on the synthesis of various factors providing resistance to high temperatures. These factors

include heat shock protein 70 (HSP70), antioxidants such as glutathione, and IGF-1. One of the responses of the

embryo to elevated temperature is the induction of apoptosis, which is associated with the activation of embryonic

genome. Owing to the apoptosis, cells damaged by high temperature may be eliminated from the embryo, which

increases their chance of survival. Precise examination of the mechanisms responsible for the development of

thermotolerance of preimplantation bovine embryos will enable their protection from the consequences of elevated

temperature. The aim of this review is to summarise experiments in which in vitro embryo production

system was used to estimate the influence of elevated temperature on cattle fertility.