Heat Stress - What’s the Hype?
By Catherine Mathews, Marketing Communications Specialist for Micro-Nutrition
As we enter the spring and summer months, many of us are thinking of all the fun outdoor activities we will finally be able to do. But while we’re enjoying our cookouts and picnics, our livestock may be struggling to cope with the elevated temperatures and humidity.
Heat stress costs the dairy industry over $897 million annually in losses attributed to decreased performance, increased mortality, and decreased reproduction resulting specifically from heat stress (St. Pierre et al., 2003). Factors contributing to heat stress include air temperature, humidity, wind speed, and solar radiation. Cattle experience heat stress when they cannot physically cope with their environmental conditions.
Producers know heat stress can have severe impacts on cattle, but what exactly happens to a cow experiencing heat stress?
A Progressive Problem
While the impact of heat on an animal may seem rapid, heat stress actually occurs in progressive steps, from mild to extreme.
One of the first signs of mild heat stress is visible discomfort and a reduction in activity. When the temperatures and humidity rise, cattle that are experiencing mild stress typically will seek out shade or the coolest place they can find. Like humans, cattle will also experience increased sweating when experiencing mild heat stress.
Cattle that are under moderate heat stress will exhibit decreased feed intake and increased water consumption. A quick, visual way to assess moderate heat stress is to look at the water supply. Many times, cattle will crowd the supply when they are under moderate heat stress. Another visual identifier is panting. Cattle pant to increase their respiration rate. They exhibit this behavior when evaporative heat (sweating) is not enough to cool them down. A fourth sign of moderate heat stress is increased heart rate. The heart rate increases to pump more blood towards the skin to help cool the animal.
When cattle are experiencing severe heat stress, panting, and sweating are not enough to cool them off. During a severe heat stress event, cattle will stick their tongue out in an attempt to cool off. The protruding tongue can lead to excessive drooling, thereby reducing the amount of saliva reaching the rumen. This reduction in saliva reaching the rumen can create an increased risk of ruminal acidosis.
Another impact of severe heat stress takes place at the cellular level in the intestines. Severe heat stress reduces the amount of blood flow to the intestinal walls because most of the blood is being pumped toward the skin in an effort to cool the animal. This reduced blood flow creates a potentially dangerous situation as the cells become dehydrated, breaking down the intestinal barrier and allowing pathogens to enter the blood stream. Damage to the intestinal barrier combined with oxidative stress can lead to a condition called leaky gut.
At this level of heat stress, affected animals are unable to physically respond to the stress on their bodies. Extreme heat loss can lead to death.
If the animal survives an extreme heat stress event, it will likely take time to recover and return to typical production levels. Death from extreme heat stress is most often a result of the animal’s heart not being able to keep up the high rate of pumping required to eliminate the heat, leading to heart failure during the heat event. If the animal survives the heat event but dies days later, this is generally from the effects of pathogens in the blood stream from damaged intestinal barriers.
Animals should never reach the level of extreme heat stress. Best management practices and proper animal husbandry should be in place to prevent this from occurring.
What you can do
As producers and caretakers, it is our job to ensure that our herds are well-managed, and we are prepared to face periods of increased heat. Heat stress is a progressive problem and early identification of the symptoms can mean the difference between life and death.
To learn more about best management practices for heat stress, download our guide.