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

Part 1

We hear about it all the time. Too much stress in the workplace. Too much stress at home. Stress on the highways causing road rage. The economy causing stress in our lives due to loss of jobs, high costs, irritation at the government for how they are handling issues. So on and so on.

But what about stress in the pasture? Often times we don't give much thought to the fact that our cow herds endure a lot, but it is definitely there. Most commonly we think about it when we wean calves or load cattle on a truck for a long transport. But it's more complicated than that. A lot more complicated.

This article will explore some of the different types of stress that are common in cattle out on pasture in our breeding herds and the effects it can have on these animals if not managed in some way.

Environmental Stress

No, this is not referring to cattle worrying over climate change due to their carbon foot print. With the exception of total confinement feeding operations (which are not too common) most cattle are subjected to the elements the vast majority of their lives. And given the fact that there are no perfect “weather zones,” cattle are going to be subjected to hot, cold, dry or excessive wet. Some may experience all of these at some point; some only one or two of these. Extreme conditions can include excessive prolonged droughts, blizzards, hail, sleet, hurricanes, tornadoes, heat waves, etc. Even moderate deviations from the “thermoneutral zone” (the temperature range where no added energy is required to either heat or cool the body). Moisture levels contribute to this problem. Wet conditions increase the temperature low thresholds of this range just as humidity decreases the high temperatures. Depending on pasture or pen situations, wet conditions can increase mud levels dramatically also increasing the energy required for simple grazing activities. This past year has been a prime example in many areas where persistent rain or snowfall during much of the late fall and winter resulted in prolonged muddy conditions on many operations. These conditions dramatically increase maintenance energy requirements. This resulted in increased forage (hay, silage) consumption by cattle and a need for increased supplementation to maintain body condition scores necessary for normal calving and subsequent breeding activities. Research has shown that as little as 4” of mud reduces feed efficiency in feedlot cattle by 10% or more.

Other problems created during prolonged periods of excessive rain and snow during the late fall, winter and early spring include:

1)      Reductions in stockpiled forages otherwise used for grazing.

2)      Increased levels of loss (shrink) in hay and other fed forages.

3)      Increased levels of loss (shrink) in fed supplements.

4)      Increased dystocia or calving losses.

5)      Increased time periods to rebreeding.

6)      Increased levels of sickness (morbidity) in all classes of cattle.

For the typical cow calf operation, steps to offset excessively wet conditions are challenging to establish. Obviously keeping cattle out of low-lying areas is necessary, especially if these areas are prone to flooding. Providing access to shelter of some type is helpful. Providing supplements in covered feeders also can help reduce losses.

Other Environmental Issues

As summer approaches we begin thinking about heat and whether or not our air conditioning systems are functioning properly. Heat stress is a common topic of discussion among dairy cattle producers but heat has similar stressful effects on beef cattle. The thermocomfort zone for cattle varies depending on a large group of factors including body condition, hair coat length, plane of nutrition, health, breed, age and acclimation. In general, cattle do not handle heat as well as humans. 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 70 degrees F. What that means is that producers need to consider the fact that their cattle are probably hot even when they themselves are not.

In the initial or early stages, when cattle start to suffer from heat, the early signs are not always apparent. Feed and roughage intake may drop a little but the animal may be fairly uncomfortable way before that. As cattle heat up and feed intake drops, cattle begin using additional energy in order to help keep themselves cool, therefore, heat stress reduces production and efficiency. Once this performance level drops it becomes 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. This often results in reduced breeding activity, reduced cycling and lower conception rates. A confounding 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.

Another area of concern is immune response. This is especially critical in newly weaned cattle 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. Additionally 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. Also, 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 is conditions are somewhat dusty. Regardless, in many cases heat stress is only one stress component in the overall physiological challenges these cattle encounter.

It has been determined that three elements are critical in hot weather situations: intensity of heat, duration and the opportunity to cool down at night. The heat intensity means that the combination of heat and humidity create a seriously debilitating or killing situation. If you add an inch or more of rain just prior to an intense heat the humidity level is increased significantly. This elevates heat losses substantially.

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.

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

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

•      Gasping and lethargic.

Often, symptoms of heat stress may 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.

Planning is the Key

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.

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

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 and availability of adequate water. Pens facing east or southeast have been shown to have the radiant heat load and showed the lowest death losses. Pens or pastures with features that obstruct air flow should be avoided. 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. One would think this is a “no-brainer” but surprisingly enough, every year cattle are lost because they are place 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 2 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 48,000 gallons of water per day. In a 10,000 head feedyard where the average animal size might be 800 lbs this daily requirement would equal almost 4 million gallons! Obviously you'd better have a good water supply. Additionally, cattle in a confined feeding situation need at least 3 inches of linear space at the waterers. Water has long been known as the single most important nutrient in an animal's diet. This is especially true during the heat of the summer. Finally, thought needs to be given to a contingency plan in the event that something might interrupt the water supply.

3)      Shade. Although shading does not decrease air temperature, reducing radiant energy (sun exposure) to cattle is critical. In pastures with substantial numbers of trees, we often take shades for granted. 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 excess 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 nut in northern climates they must be able to handle the weight of snow in winter. 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% 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 3.5 degrees. If it is absolutely necessary to handle cattle during hot weather periods make sure it is done between midnight and 8 a.m. and never after 10 a.m. Even in the evenings after the sun has set, it takes a minimum of 6 hours to dissipate body heat and this is contingent on what the air temperature is at night. Holding and processing areas should have shade and sprinklers available.


We have to recognize that because we have only limited control of the environment, stress on the animal is unavoidable. Using common sense and planning, however, can reduce the effects. In the next part of this series we will continue to examine stress in cattle, its effects and how it can be lessened or even avoided.

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


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