by: Stephen B. Blezinger
Ph.D., PAS

If you follow the articles I contribute here at all you know that I am not a proponent of the whole global warming frenzy (or rather “anthropomorphic climate change”). However, as I write this here at the end of July/early August 2010 I am a little inclined to give it some credence. Not really, but it IS hot as Hades here in Northeast Texas! On a number of occasions before we have talked about heat and heat stress and how it affects the cattle herd. As I review the calls and discussions I have had over the last month or so, I felt it might be a good idea to review some of the facts and factors concerning heat, heat stress and how it affects your cow herd.

We tend to think that the heat affects only dairy or feedlot cattle. At least these are the industry sectors we hear the most from when it comes to this topic. But the effect of heat on cattle is not limited to these groups. Beef cattle on pasture, young and mature alike are also affected by high temperatures and high humidity. The animal and production losses represent millions of dollars not to mention the time and effort of dealing with the situation.

How and Why Heat Affects Cattle

Unless your operation is truly out of the ordinary you don't have an extensive means for getting your cow herd out of the heat. And they surely don't have access to the AC systems that most of us enjoy. That is with the exception of a few show cattle folks that have actually build “coolers” for their cattle in an effort to grow hair (which, by the way, is as much related to day length as it is to temperature).

A concept every cattle producer needs to become familiar with is thermocomfort zone. This is the temperature range at which all organisms (including people) are the most comfortable and thus do not expend added energy to cool their bodies. The thermocomfort zone for cattle varies depending on a number of factors. These include:

• body condition – thinner or fatter cattle feel the effects more

• hair coat length/density - compare Brahman animals to Angus

• plane of nutrition – better nutrition improves the animal's ability to handle heat

• health – poor health decreases the animal's ability to handle heat

• breed – again, compare Brahman or Brahman crosses to English or European breeds

• age – young or older cattle have a more difficult time with the heat or cold

• acclimation – do not bring cattle from Wisconsin to Texas in July!

In general, cattle do not handle heat as well as humans even though they spend their lives out in the environment. In the midst of a typical summer, cattle are generally less comfortable than humans at the same environmental temperature. Something to consider is that cattle begin feeling the effects of the heat at about 70o F. Less if the humidity is high. What that means is that producers need to consider the fact that their cattle are probably hot even when they themselves are not and that this may be affecting performance in some way.

In the initial or early stages, when cattle start to suffer from heat, the early signs are not always apparent. In pasture cattle, forage intake/grazing patterns may drop a little but the animal may be fairly uncomfortable way before that. As cattle heat up and intake drops, cattle begin using additional energy, generally from their own fat reserves, in order to help keep cool, therefore, heat stress reduces production and efficiency. Once this performance level drops it can be very difficult to get it back.

In breeding cattle, we see a similar response in terms of nutrient or feed intake and energy metabolism in an effort to stay cool. Commonly the result is reduced breeding activity, reduced cycling and lower conception rates. A complicating factor in this scenario is that at a time when cows are hot and not grazing as heavily the forage quality has also deteriorated so that the roughage or pasture that is consumed is lower in nutrients as well as less digestible. This makes a pretty strong case for summer supplementation programs as well as a strong case for breeding cows for calving during the cooler months of the year.

Another area of concern is immune response. This is especially critical in newly weaned cattle and those that are to be preconditioned and backgrounded. It becomes even more of a concern if these cattle are transported, especially if they have been run through a sale facility of some type and co-mingled with other cattle. Although the exact relationship between heat stress and immune function is unclear, we do know that since much of the animal's maintenance energy is being used to cool itself, the requirements of the immune system may go unmet. This includes ALL nutrients as dry matter intake is decreased. We also know that under different types of stress, the body tends to deplete itself of critical nutrients such as zinc and copper that are vital to immune response. It has been determined that under stress, the adrenal gland will secrete steroid mimicking hormones that will essentially turn off the immune system. Yet another factor is that respiration rate (panting) is accelerated which increases the susceptibility to respiratory disease, especially if conditions are somewhat dusty. Regardless, in many cases heat stress is only one stress component in the overall physiological challenges these cattle encounter.

Signs of Heat Stress

Producers need to watch the cattle as well as the environment and be familiar with the signs of heat stress. Signs of heat stress can include:

• Restlessness and crowding under shade or at water tanks. The crowding intensifies the problem.

• Open-mouthed breathing (panting), and increased salivating.

• Increased respiration rates, i.e. rapid breathing. (Moderate heat stress: 80 to 120 breaths per minute, Strong heat stress: 120 to 160 breaths per minute, Severe heat stress: over 160).

• Lethargy, lack of normal movement, reduced grazing activity.

• Increased grazing at night, early in the morning

In many cases, symptoms of heat stress can look like respiratory disease. Remember that since cattle do not perspire (sweat) well, they have to use the respiratory system to remove excess heat from their system. Brahman cattle are well known for being more heat tolerant than other breeds. They have more highly developed sweat glands than do English or European breeds which gives them a greater capacity to sweat. They also commonly have more loose skin (dewlap, sheath areas) than do English or European breeds thus increasing cooling as related to evaporative capacity of the animal.

Planning for High Temperatures

Having a solid plan can make the difference between weathering hot, humid periods with a minimum of production losses and finding yourself in an emergency situation. Considering what to do about heat stress periods must start long before it gets warm. Some key factors include:

1) Identifying high risk cattle. High risk cattle may include the following:

a. Newly arrived cattle that have experienced a fair amount of weaning, processing or transportation stress.

b. Finished or nearly finished cattle, especially heifers.

c. Cattle that are or have been grazing infested fescue pastures. High Endophyte/ergovaline intake is well known to increase the body temperature of affected cattle.

d. Cattle that have been sick in the past and may have some preexisting lung damage (chronics).

e. Black or very dark-hided cattle.

f. Heavy bred cows that will calve sometime during the summer months.

g. Older cows.

h. Cattle which may be somewhat thin due to inadequate nutrition.

High risk cattle should be placed in pastures or pens which will help them reduce their heat loads as best possible. These pastures or pens should contain adequate shading, decent airflow and availability of adequate good quality, fresh water. Pens facing east or southeast have been shown to have the lowest radiant heat load and showed lower death losses. Pens or pastures with features that obstruct air flow should be avoided (pens up agains solid walls, especially unpainted sheet metal (tin) that reflect light/heat). Also areas next to irrigated crops should be avoided since this also increases the humidity in the air. Finally, producers need to control flies since flies cause cattle to bunch which also restricts air flow.

2) Water Availability. Water has long been known as the single most important nutrient in an animal's diet. Every year cattle are lost because they are placed in areas with insufficient water. Drinking water is the most efficient and fastest way for cattle to reduce body temperature. In higher temperature situations, demand is increased as well. At temperatures above 80o F, they may need in excess of two gallons per hour for each 100 lbs of body weight. Heavily lactating cows may require even more if milk production is to be maintained. For a herd of 100 average sized cows, that would require over 50,000 gallons of water per day. And remember availability of good quality water has a direct effect on feed intake and subsequently energy intake. Additionally, cattle in a confined feeding situation need at least 3 inches of linear space at the waterers. A final issue concerns water quality. Water provided in ponds heavy with silt or algae or where cattle can enter the water supply is typically consumed at a lower rate than clean water supplies, well water or water from county or municipal systems. Research has shown that cattle will preferentially consume well or system water over pond water in most cases and that intake is significantly higher from these sources.

3) Shade. Shading reduces radiant energy (sun exposure) to cattle. In pastures with substantial numbers of trees, we often take shades for granted. In feedyards or growing operations research has shown that adequate shading can cut death losses in half. Shade also increases feed or nutrient intake. Constructed shades should be from 7 to 14 feet high and provide from 40 to 50 square feet per head. In pastures with trees for shade, this number should be increased in order to prevent excessive grouping which can and does tend to kill the trees over an extended period of time. It may be necessary to construct some additional shades in order to increase the shade availability in pastures even when trees are available. Constructed shades can be made of many different types of materials. Some new shade designs have been produced over the last few years which incorporates a high strength mesh material that will reduce as much as 95 percent of radiant energy, handle environmental challenges (wind, some ice and snow) and are quite cost effective.

4) Handling and processing. DO NOT handle cattle in hot weather if at all possible. Research has shown that movement or handling of cattle during hot weather can change (increase) their body temperature from .5 to 3.5oF. If handling is absolutely necessary do so between midnight and 8 a.m. and never after 10 a.m. Holding and processing areas should have shade and sprinklers available.

5) Sprinklers. In confined cattle feeding situations, sprinklers can have a multifold benefit to cattle. Initially they are quite useful in keeping down the dust. On very hot days they can be considered an insurance against death losses. It can also help reduce ground temperature as well. Cattle need to be really wetted down, not just misted. Sprinkling should take place intermittently over the course of the day to prevent the development of a high humidity situation. Sprinkling of two to three minutes followed by a break of 20 to 30 minutes seems to work the best.

6) Feeding. As discussed earlier, hot weather often dictates a need for supplementation of pasture cattle. With intakes down, nutrient intake can only be maintained by feeding a more concentrated supplement to offset the reduction.


During the heat of the summer it will be impossible to keep cattle perfectly comfortable and performing as normal. Doing some homework, planning the production calendar and identifying critical issues can help the producer effectively reduce heat stress in breeding, growing and finishing cattle. This helps maintain profits and productivity even when the environment is less than cooperative.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at 667 County Road 4711, Sulphur Springs, TX 75482, by phone at (903) 352-3475 or by e-mail at For more information you can also visit


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