Heat stress in our animals is always a top concern for me. I was especially concerned when we first bought our Highland cattle. All cattle are affected by heat stress, and after learning more about the breed I would venture to say that Highlands may tolerate it better than other breeds. Heat stress can be identified by signs like panting, slobbering, and grouping together. When the temperature heat index (THI) is 72 degrees Fahrenheit or higher your cattle are beginning to really feel the effects of the heat.
Cattle don’t sweat effectively and their rumen creates an added heat source. They rely on respiration to cool themselves. Additionally, cattle accumulate a “heat load” during the day and dissipate it during the cool night. However, if the nights don’t adequately cool down (less than 80 degrees) they carry that load longer and it continues to accumulate. In total, it takes around 6 hours for cattle to dissipate their accumulated heat load from the day. Cattle with increased fat deposition will have a more difficult time dissipating their heat. This is good news for Highland owners, because Highlands have a hair coat. The coat thickens in the winter to keep them warm (meaning less fat storage than other breeds to keep them warm) and it SHEDS in the summer to help keep them cool. A good brush does wonders for Highlands in the spring and summer. You will be amazed at how much hair you can remove.
Why should you be concerned about heat stress in your cattle? Many of us who raise Highlands have cow-calf operations, and heat stress can cause reduced fertility. This is especially a concern for spring calves since breeding occurs during summer. One reason this occurs is because increased stress results in increased cortisol which in turn causes a reduction in estradiol (reproductive hormone). It also reduces the length and intensity of estrus/heat. It increases the time between estrus events as well (meaning fewer times of heat while you have the bull out with the girls). Additionally, it causes “silent ovulations” meaning that the bull has a more difficult time identifying the time of estrus/heat and this will result in decreased mounting activity. When cattle are experiencing heat stress they can begin to have a negative energy balance (reduced nutrition due to decreased intake as a result of the heat stress) and this suppresses other necessary reproductive hormones. Furthermore, when a cow or heifer is in a state of heat stress there is a reduction in blood flow to the uterus, which makes for unfavorable conditions to support a fetus. This can result in increased losses of the early embryo. A bull’s fertility is also negatively impacted by heat stress and can result in a reduced quality of sperm. They also tend to be less active during times of severe heat. When it is hot, they can usually be found laying down in the shade or near a water source. This reduces the amount of time they are grazing and breeding during daylight hours which can reduce your reproductive rates overall.
Now that you know how heat stress can disrupt your cow-calf operation, how do you go about reducing heat stress? First, make sure your cattle are at an ideal body condition score before summer starts. Because the nutritional intake can be reduced and energy demand can be higher during times of intense heat, it is important that your cattle have a good body score in the beginning of summer to ensure they have nutrient stores they can pull from if necessary. This is important for overall health, but also with regard to reproduction. Adequate nutrients are necessary for successful reproduction to occur. Second, it has been shown that offering vitamins and minerals before the onset of summer can help reduce the negative effects of heat stress on reproduction. Some specifically formulated minerals claim to help reduce heat stress in cattle and many people feel they can see the difference in their cattle while they feed it during the hot summer months. One such vitamin is VitaFerm Heat. You can find local dealers on their website. It is important to remember that because cattle may experience reduced intake overall, it can be helpful to offer a little feed during the cooler parts of the day to ensure that they are receiving adequate nutrition. If feed is given to help increase nutrient intake, it should be fed 2-4 hours after peak environmental temperature. This is because their rumen produces heat as it digests food, and it peaks in temperature about 4-6 hours after feeding. If you feed in the morning, the rumen temperature will peak around the hottest part of the day.
Additionally, offering adequate shade, access to clean and palatable water, and working or moving cattle during the coolest times of day can reduce the amount of heat stress that your cattle experience. It is recommended that cattle should not wait longer than 30 minutes to be worked in a holding area. Also, many recommend that cattle should only be worked in the early morning and not in the evening (even if temperatures have cooled down). This is because cattle’s peak temperature is about 2 hours after the peak environmental temperature. Cattle dissipate their heat by respiration and they lose water during that process due to evaporation. For this reason, their water requirements are much higher during hot summer months. Consumption of water is the quickest way for them to reduce their body temperature.
If you add a shade structure keep these points in mind. First, there should be 20-40 square feet of shade per animal. An east-west structure (with regard to length) is said to have a cooler ground under the shade. However, if the area is muddy it may be best to have a north-south orientation to increase drying (because of the way the shade moves across the ground during the day). Also, the structure should be at least 8 feet tall to ensure adequate airflow.
Controlling flies can also help reduce heat stress. This is because cattle often group together to reduce the surface area available to biting flies. When grouped together, they have a more difficult time dissipating heat and getting access to airflow, which makes it harder to cool off. Reducing breeding areas for flies and using insecticides can help.
Using sprinkler systems can also help reduce heat stress, although the animals must be properly introduced to it or they will avoid the spray when they really need it. It is recommended that the stream is adequate enough to soak the animal and not just mist the air. To prevent mud and increased humidity in the area, the sprinklers should be turned on periodically but not left to run all day. Thermal shock can occur if very cold water is used in a severely overheated animal, so introducing the cattle to the area before severe heat stress occurs can get them used to using the area before they get too overheated.
Follow the link below to see a heat stress forecast in your area. It takes into consideration the forecasted temperatures and humidity. A 7-day forecast is provided.
http://www.ars.usda.gov/Main/docs.htm?docid=20426
Resources:
https://extension.usu.edu/animalhealth/research/heat-stress-and-reproduction-in-beef-cattle
Disclaimer: I am not a veterinarian and strongly advise you discuss any potential diagnoses and treatment options with your veterinarian first. This article is for informational purposes only. Riebel Farms LLC and its authors will not be held liable for any use of the information provided.