by: Curt Vlietstra, DVM
Even though we had a brutal winter, and the normal spring warm-up seemed like it would never come, the heat of summer is inevitable in this area. The combination of heat and humidity can be extremely hard on livestock, particularly cattle. Both dairy and beef cattle have their own challenges when it heats up in the summer, but some of the issues are shared. Here are a few comments on the effects of heat stress, as well as some of the important ways to minimize the impact of heat and humidity.
- Heat stress occurs when the THI (temperature-humidity-index) gets above 80. This can happen when the temperature is below 70 F if it is extremely humid. If you remember last summer, the worst of the heat’s effects on livestock happened because it didn’t cool down at night and the humidity remained high. The weather services often issue alerts when the THI reaches dangerous levels for livestock.
- The primary negative impact of heat stress is decreased feed consumption, which will either decrease growth in beef cattle or decrease milk production in dairy cattle.
- In addition to decreased performance from insufficient energy, decreased feed intakes often result in sub-optimal levels of vitamins and minerals. This may affect health, reproduction, and other vital bodily functions.
- In an attempt to dissipate heat, the body will increase blood circulation near the skin, which takes blood away from digestive functions. This can lead to decreased feed efficiencies and also lower the functionality of the liver, an organ that is extremely important at detoxifying the body and regulating energy in fresh cows.
- Increased water availability and consumption is an expected consequence of heat stress. As necessary as water is, increased consumption can lead to increased urination and nutrients excretion in the urine, compounding decreased nutrient intake.
Strategies for dealing with heat stress involve combinations of cooling through ventilation and/or sprinklers, shade, fly control, increased water availability, and nutritional adjustments.
- Numerous studies and on-farm observations support the use of a combination of fans and sprinklers if possible. Anytime you are able to utilize sprinklers, remember to use a high volume of “soaking” water, and not a mist. The mist will increase the air humidity, and fine water particles can stick to the hair on cattle and act as an insulation layer, preventing the body heat from escaping. Cattle should be wet before extreme heat, and cattle under extreme heat stress should never be shocked with very cold water.
- Maintaining hydration and electrolyte balance is very important during times of heat stress. Encouraging water intake by providing fresh, cool water, and plenty of it, is very important.
- Feeding additional electrolytes or providing them in the water makes water movement and storage in the body more efficient and can actually lower the core temperature.
- Flies cause cattle to bunch. Fly control should be part of heat abatement.
- In an open lot situation, the following are important to consider:
- Digestion takes energy and increases the body temperature. This is especially true of rumen fermentation for rations with any considerable amounts of forages.
- The increased body heat from eating takes place four to six hours after eating, so feeding in the morning will result in the heat of the day increasing as the body heat increases from eating.
- Shades are important, especially for black cattle. Shades oriented east-west will provide consistent shade throughout the day. Shade oriented north-south will “move” throughout the day, forcing the cattle to move which can entice feeding and also provide the sun a chance to dry yards if mud is an issue from sprinkling.
- Cattle “accumulate” heat during the day and attempt to dissipate this heat at night, so wetting the cattle prior to evening will speed up the cool down without adding to the pen humidity as much as sprinkling during the day.
- Reducing the energy of the ration by a few percent is thought to reduce the effects of dietary metabolism on body temperature, but would also decrease rate of gain. Any nutritional strategies should be discussed with your nutritionist.
