Dairy cows suffer from heat stress when the temperature and humidity of the environment exceeds the range specified for normal activity (already above 25° C and only 50% humidity), then the heat load causes a disturbance in the heat output of the body. Temperature regulation is connected with physiological and behavioral changes.
Behavioral changes caused by heat stress
During the high temperatures, cows look for shade, cool and airy beds, drink much more water, increase the loss of body liquids, during nozzle and sweating, the amount of liquids given away in the form of feces and urine decreases, appetite falls, rumination, feed intake and activity, heart rate increases.
Physiological changes
When heat stress lasts for quite a long time, the production of growth hormone, catecholamine, glucocorticoid and thyroid hormones is reduced, the basic metabolism and thus heat production is reduced. At the same time, the living and production needs of cattle are at the pre-stress level. Then an energetic and mineral-vitamin deficit appears, milk production decreases, and the consequences of heat stress can have long-term effects, which we will observe even a few months later, in the form of higher predisposition to metabolic diseases, mastitis or problems in reproduction (miscarriage, problems in calving).
Decrease in rumination and milk production – high THI
The cow comfort zone is described by the THI (temperature humidity index) value, which should be below 71 points, 72 to 79 points is described as mild stress, 80 to 89 as moderate stress and over 90 as strong stress.
THI monitoring in the barn
Considering that temperatures are high practically all summer long and relative air humidity is also quite high, due to the high precipitation in recent times, heat stress will appear in many buildings – even in this modern, high and airy one. The loss of milk in the whole lactation can be 10-15%.
Monitoring activity, rumination, feed intake or decrease in daily milk production and measuring temperature and humidity in the building at the same time is time consuming and nobody has time for this in practice. And these are very important indicators of our animals’ health and welfare.
The breeders use different solutions – from advanced air conditioners, air mixers, sprinklers to ordinary domestic large windmills. On the pasture, in turn, they provide shelter from the heat and constant access to water. Particular attention should be paid to tie-stall barns where the cows cannot change location and choose a cooler place in the barn.
Monitoring systems for animal behavior are a helpful solution. In addition to a biosensor for activity (rumination, feed intake or inactivity time), an environmental biosensor is also available which shows continuously whether cows in the building are exposed to heat stress.
Several such sensors can be installed in the livestock building and monitored the individual zones. This allows you to assess the quality of ventilation for the entire building and thus eliminate areas that are unfavourable for the animals.
This allows for a quick reaction of the breeder and counteracting the effects of heat stress – loss of milk, expenses connected with treatment of diseases and removing of which could have been avoided.
