G2121

Heat Stress — What You Should Know to Make Livestock Shows a Success

Heat stress is hard on livestock, especially if it is in combination with high humidity and low wind speed. The degree of heat stress is dependent on the animal’s activity, body condition, coat cover and color, and disposition.


Lindsay M. Chichester, Extension Educator
Terry L. Mader, Extension Beef Specialist


Signs of Heat Stress

Signs of heat stress (depends on species) may include animals bunching, seeking shade, panting, slobbering or excessive salivation, foam around the mouth, open-mouth breathing, lack of coordination, and trembling. (Figures 1 and 2). If these symptoms are observed, assume the animal has a heat load. Immediately try to minimize the stress to the animal, especially its handling or movement.

Previous health of individual animals is an important risk factor; animals that have had past health problems will be more affected by heat stress than animals with no prior health problems. These animals will generally be the first to exhibit signs of heat stress and be the most severely affected.

Figure 1. Cattle undergoing moderate to severe heat stress exhibit open mouth breathing and excess salivation.
 
Figure 2. A beef animal undergoing severe heat stress exhibits open mouth breathing with tongue out, head extended.
Figure 1. Cattle undergoing moderate to severe heat stress exhibit open mouth breathing and excess salivation.   Figure 2. A beef animal undergoing severe heat stress exhibits open mouth breathing with tongue out, head extended.

Effects of Heat Stress

Hot weather and high humidity can reduce feed intake, weight gain, reproductive efficiency, and milk production, while increasing susceptibility to disease. Changes in behavior and even death can also occur.

The comfort zone for animals varies depending on age. Young animals generally have a narrow comfort zone between 45°F and 80°F; while the range in temperatures of the comfort zone of mature animals can be wider. For example, with feedlot animals and mature cows the comfort zone can range from below zero in the winter to about 75°F in the summer. Bos indicus (humped cattle) do have better heat coping capabilities and can easily tolerate temperatures above 90°F (Table I).

Table I. NOAA’s National Weather Service. (Source: http://www.nws.noaa.gov/os/heat/index.shtml.)
G2121 Table I. NOAA's National Weather Service.

What Is a Heat Index?

Environmental stress is dependent on temperature, humidity, wind speed, and solar radiation, which is best determined by an index. The index that is most commonly used is called the Heat Index, commonly reported by many media outlets during the summer. This index, used for humans, has a threshold that is very close to the livestock temperature-humidity index.

The following guidelines should be followed for show animals:

Keep in mind that using the heat index value does not account for nighttime cooling, which can be a good indicator of overall heat stress. When animals do not cool down at night, they become compromised and are less capable of handling a heat load.

Management Options

Management options include providing shade, ventilation and air flow, clean and cool water, wetting, cool water drench, and sprinklers or hoses.

Water Requirements

At 90°F, water consumption can be almost twice that at 70°F. For example, on days where the temperature exceeds 80°F, cattle may need more than two gallons of water per 100 pounds of body weight. Also, water requirements vary from species, to species and on metabolic and physiological needs. For instance, water needs will vary depending on the weight of the animal, lactation, and moisture of the feeds being consumed. Water prevents dehydration and allows heat to dissipate through sweating and urination.

The amount of water an animal drinks will be largely dependent on the amount of water lost through evaporation from its skin or lungs, as well as through urination. If the environmental temperature and/or physical activity increase, then it is safe to assume that water losses through evaporation and sweating will also increase.

Avoid Overworking the Animals

Body temperatures of livestock exposed to high daytime temperatures tend to peak in the early evening, decline during the night, reach a low point in the hours just before sunrise, and rise again slowly throughout the day. It is recommended to work/process livestock in the morning. Avoid working them in the late afternoon/early evening when their body temperature is already high. Processing cattle can elevate their body temperatures ½ to 3½ degrees.

Confinement

Animals in confinement will usually have higher heat loads than animals grazing pasture. This is due to possibly less air movement and less shade availability in a confined area. Also, there is more exposure to radiant heat associated with concrete or dark, bare soils.

Animal Weight and Body Condition

Livestock heavier in weight or having a higher body condition score are generally more susceptible to higher heat loads than livestock lighter in weight, or with a smaller body condition score.

Hide/Pelt Color

Usually, animals that are dark hided or dark pelted are more susceptible to heat stress than their light hided/pelted counterparts. It is best to assume that all animals are susceptible to heat stress, regardless of hide/pelt color.

Transportation

If possible, avoid transporting livestock during heat stress periods. If transportation cannot be delayed, it should be done in the evening or early morning when temperatures are cooler. The transportation of heat-stressed livestock to a harvest facility may have a negative effect on carcass quality, such as dark cutters in cattle, or PSE (Pale, Soft, and Exudative) in pork.

Livestock Show Recommendations

If the weather report in the morning indicates a heat index of 115°F or above, consider postponing a livestock show to early the next morning. This is a rule that may need to be added to fair books and discussed with 4-H councils and/or fair boards. It is important to keep in mind that animal and exhibitor health should be the primary deciding factor.

Summary

It is important to take precautions during the summer months to ensure that animals suffer as little as possible from heat stress. Provide livestock with shade if possible, and plenty of clean, cool water. Try to limit other activities that may increase their stress, including movement and/or hauling. If an animal shows severe heat stress symptoms, contact a veterinarian immediately.

Resources

Boyles, S. (n.d.). Heat stress and beef cattle. Ohio State University Extension. Found online Oct. 12, 2011 from http://beef.osu.edu/library/heat.html.

Collier, R. J. and Zimbelman, R. B. (2007). Heat stress effects on cattle: What we know and what we don’t know. Department of Animal Sciences, The University of Arizona. Found online Oct. 12, 2011 from http://ag.arizona.edu/ans/swnmc/Proceedings/2007/Collier_2007SWNMC.pdf.

Epperson, B. (2006). Handling heat stress in cattle. South Dakota State University Cooperative Extension Service. Found online Oct. 12, 2011 from http://www.sdstate.edu/abe/wri/water-quality/upload/ExEx11011.pdf.

Mader, T. (2011). Heat stress on show animals. University of Nebraska–Lincoln. Personal communication on Oct. 02, 2011.

Mader, T., Griffin, D., and Hahn, L. H. (2007). Managing feedlot heat stress. NebGuide G1409. Found online November 4, 2011 from http://www.ianrpubs.unl.edu/sendIt/g1409.pdf.

Rasby, R. J. and Walz, T. M. (2011). Water requirements for beef cattle. University of Nebraska–Lincoln. Found online Oct. 12, 2011 from http://www.ianrpubs.unl.edu/sendIt/g2060.pdf.

This publication has been peer reviewed.


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Index: Beef
Miscellaneous
Issued February 2012

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