HEAT STRESS VS. CATTLE REPRODUCTION

Abstract

Dairy cattle are constantly exposed to many stressful situations activate changes in the
functioning of the entire body of cows. Heat stress has been a major challenge for
veterinarians and cattle producers in recent years. It is the result of external forces
associated with high air temperature, causing changes in the body from the subcellular level
to the whole body. These changes are part of adaptation to new environmental conditions
and occur to avoid physiological dysfunctions caused by stress. The Holstein-Friesian breed is
considered to be sensitive to high air temperature. Management of dairy cattle under heat
stress conditions should consider animal welfare, which is a state of harmony between the
animal and the environment, expressed in high quality of life. Environmental factors such as
air temperature, relative humidity, wind speed, and the intensity of solar radiation impact the
functioning of dairy cows. Elevated temperatures and relative air humidity prevent the
removal of excess heat from the cow’s body. Heat is accumulating in animal organisms and
growing body temperature, which in turn disturbs thermoregulation. Physiological methods of
coping with heat stress include increased respiratory rate, panting, increased heart rate,
sweating, decreased milk, and reproductive performance. Behavioral responses also appear,
for example, increased thirst, reduced food intake or feed consumption in cooler parts of the
day, looking for shade, and reduced physical activity. The reproduction of high-yielding cows
is exposed to negative changes caused by high temperatures. Dairy cows are more likely to
lose their pregnancies in summer than in winter. The improvement of fertility in the summer
period can be obtained using the available knowledge about the influence of heat stress on
the reproductive process. Heat stress can cause physiological changes in the ovaries,
fallopian tubes, uterus, and embryos. Alteration of the fallopian tube or uterus environment
may be due to disturbances in circulating hormones caused by heat stress, which affects
embryonic development. Maintaining proper fertility of cows in a situation where the
temperature and air humidity exceed the values specified for cows is very important for
maintaining the profitability of the farm. The most important thing is to recognize heat stress
conditions as early as possible in order to implement strategies to prevent its further
development as soon as possible. The presentation will provide the current updates of heat stress
problems in cattle reproduction.