Combating Heat Stress in the Summer Months

As we gear up for summer, it's time to be thinking about the challenges a new season brings. One of the challenges of the hot and humid days of summer is heat stress. Heat stress can negatively impact both animal productivity and welfare. Monitoring weather forecasts in the summer and being aware of the risk factors, signs, consequences, and mitigation strategies for heat stress can help to minimize its effects.

Why is heat stress a problem?

Heat stress has a negative effect on animal performance and welfare. It has been associated with several issues including reduced feed intake and gain in feeder cattle and decreased fertility in breeding animals. Severe and prolonged periods of heat stress can lead to mortality.

What are the risk factors?

To maintain temperature homeostasis, animals will produce and dissipate heat. Cattle produce a substantial amount of heat from digestion (fermentation) and also generate heat from tissue metabolism. The means by which cattle dissipate heat include convection, conduction, radiation, and evaporation (sweating and respiration). When cattle are unable to transfer heat to the environment due to environmental conditions, heat stress can set in.

High ambient air temperature is the main culprit of heat stress, however elevated temperatures coupled with high relative humidity, solar radiation, and reduced air movement can further predispose cattle to heat stress. A Temperature Humidity Index (Table 1) accounts for both temperature and relative humidity and can be used to determine approximately when cattle will begin to experience heat stress and the severity of heat stress endured.

Table 1 - Temperature Humidity Index (THI) for Livestock*

Temperature Humidity Index (THI) for livestock

*Dr. Frank Wiersma (1990) Department of Agricultural Engineering, University of Arizona, Tucson

The University of Guelph and the Ontario Ministry of Agriculture, Food and Rural Affairs have developed a heat stress app that can be used by livestock producers to assess potential risk of heat stress. To download the app or for more information, visit www.omafra.gov.on.ca/english/engineer/facts/heat-app.htm.

The extent to which heat stress affects cattle depends on age, body condition, availability and management of feed and water, access to shade or shelter, and other physiological factors. Lower nighttime temperatures tend to reduce the impact of elevated daytime temperatures on cattle because there is opportunity for heat dissipation.

Feeder cattle tend to be at increased risk of heat stress when fed high-energy diets that result in increased metabolic heat production. Susceptibility to heat stress is particularly high for cattle close to finishing with increased body condition. Coat colour can also affect susceptibility to heat stress. Dark-haired cattle are more susceptible to heat stress than light-haired cattle.

What are the signs of heat stress?

Cattle will change their behaviour in attempt to adapt to temperatures outside of their thermoneutral zone. During periods of elevated temperatures, cattle will tend to seek shade, spend less time lying down, and will look for water sources to help them cool down.

When cattle are distressed due to the heat, they will exhibit symptoms that include:

  • laboured breathing
  • open-mouth panting
  • bunching in attempt to reduce exposure to solar radiation
  • increased saliva production (drooling)

What can be done to mitigate heat stress?

  • Provide a sufficient volume of drinking water
    • Providing an ample amount of drinking water to cattle is a critical measure to reduce the effects of heat stress and to prevent dehydration. Keep in mind that water needs for cattle increase as the temperature rises. Table 2 outlines the water requirements of cattle at different stages of production and at various ambient temperatures.
    • Ensure adequate drinking space is available. Consider that more visits and more time spent at waterers can be expected during periods of hot temperatures.
  • Alter the feeding regime
    • Under normal circumstances it is a good practice to keep the feeding regime consistent. However, altering feeding practices during a heat wave can be a means of reducing the effects of heat stress.
    • For feeder cattle experiencing heat stress, Mader et al. (2002) showed that restricted feeding methods helped to reduce the effects of heat stress versus offering feed ad libitum.
    • Feeding the bulk of the diet late in the afternoon or in the evening can help minimize the effects of heat stress. The objective behind this strategy is to stagger peak daytime temperatures and rumination to reduce heat load (Davis et al., 2003).
  • Consider physical accommodations
    • For confined cattle, increase airflow by opening up curtains and allowing as much airflow through the barn as possible. Use fans to increase air movement.
    • Wetting down cattle and surfaces can be an effective means of reducing heat stress. Davis et al. (2003) showed that sprinklers were effective in mitigating the effects of heat stress through increased transfer of heat by evaporation. Sprinkling also cools barn surfaces which can increase heat transfer between animals and surfaces. Care must be taken in budgeting for adequate water supply and ensuring floors do not become slippery.
    • Provide shade (such as trees, buildings, other shading structures) where possible and ensure there is adequate space for cattle to spread out.
  • Modify handling strategies
    • Avoid shipping, processing, and any kind of handling of cattle at peak temperatures during the day. Body temperature increases with increased activity, therefore restricting animal handling to early morning or evening can help to reduce heat load.

Table 2: Approximate Total Daily Water Intake of Beef Cattle in Litres*

Cattle Class Weight Air Temperature in °C
kg lb to 4°C 10°C 14°C 21°C 27°C 32°C
Growing Cattle 185 400 15 16 19 22 25 36
273 600 20 22 25 30 34 48
364 800 23 26 30 35 40 57
Finishing Cattle 273 600 23 25 28 33 38 54
364 800 28 30 34 41 47 66
454 1,000 33 36 41 48 55 78
Lactating Cows 409+ 900+ 43 48 55 64 68 61
Mature Bulls 636 1,400 30 33 38 44 51 72
727 1,600 33 36 41 48 55 78

*Adapted from: Nutrient Requirements of Beef Cattle: Eighth Revised Edition: 2016, National Research Council

In summary, heat stress can reduce cattle performance and welfare. Having a plan to mitigate heat stress prior to the hot and humid summer months can help you respond to periods of elevated temperatures when they occur.

References:

Davis, M.S., Mader, T.L., Holt, S.M., and Parkhurst, A.M. 2003. Strategies to reduce feedlot cattle heat stress: Effects on tympanic temperatures. J. Anim. Sci. 81:649-661

Mader, T.L., Holt, S.M., Hahn, G.L., Davis, M.S., and Spiers, D.E. Feeding strategies for managing heat load in feedlot cattle. J. Anim. Sci. 2002. 80:2373-2382

Wiersma, Frank. 1990 Department of Agricultural Engineering, University of Arizona, Tucson

NRC Nutrient Requirements of Beef Cattle, 8th Revised Edition. 2016. The National Academies Press. Washington, DC

For More Information:

Martin, D. and Noecker, N. 2006. Managing Heat Stress in Fed Cattle. Ontario Ministry of Agriculture, Food and Rural Affairs.

National Farm Animal Care Council. 2013. Code of Practice for the Care and Handling of Beef Cattle.


For more information:
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E-mail: ag.info.omafra@ontario.ca