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The thermal optimum for cattle remains at a level of several degrees Celsius. Heat stress may occur in animals when the ambient temperature increases to approximately 20 degrees Celsius. Its intensity is increased not only by high temperature, but also by high air humidity, which may occur in closed buildings with insufficient ventilation.
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Heat stress cannot be avoided even more in the summer. When the outside temperature exceeds 30 degrees C, in most cases we have to forget about providing animals with optimal thermal conditions. This leaves us with the greatest possible limitation of the consequences of heat stress. However, before we write about this topic, it is worth saying a few words about the consequences of this stress. Today we will focus on the milk yield of cows.
What is heat stress?
We talk about heat stress when the animal's body is unable to maintain the body temperature typical of a given species. It results from the inability to expel heat from the body resulting from metabolism and problems with adaptation to the prevailing external conditions.
It is assumed that the thermal optimum for cattle ranges from 8 to 18 degrees C. Above this temperature, the body will have problems with proper thermoregulation, and as you can easily guess, these problems will increase in proportion to the increasing ambient temperature.
Heat stress and milk production
The physiological reaction of the body to rising temperatures is to limit feed intake, which is justified by the cows' desire to minimize the amount of heat generated as a result of metabolism. However, such a reduction in animal feeding directly translates into lower milk production. In addition, there are indirect issues related to, for example, a higher risk of metabolic diseases.
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When it comes to lactating cows, the decrease in lactation efficiency due to heat stress is approximately 30-35%. It is easy to guess that the greatest decrease in milk production will be observed in the most productive animals in the herd.
Consequences in the future
However, the decline in productivity does not only apply to animals exposed to heat stress during lactation. According to research cited by Top Gen, heat stress in dry cows causes milk production in the next lactation to be approximately 4.5 kilograms less than in animals that were not exposed to high temperatures.
Read more How to reduce the effects of heat stress in poultry?
Importantly, the effects of high temperatures are transferred even to subsequent generations. It was shown that in the daughters of such cows the productivity of the first and second lactation is lower by 3.6 and 3.4 kg, respectively. A similar decline in productivity is observed even in the next generation.
Sources:
Top Gen
Polish Federation of Cattle Breeders and Milk Producers