IMPORTANT TO UNDERSTAND HEAT STRESS CONDITIONS IN CATTLE

by: Stephen B. Blezinger
Ph.D, PAS

When I stuck my head out of the back door this morning at 6:15 am and immediately broke into a sweat I came to the conclusion that summer had, in fact, begun in Northeast Texas. That, plus later that morning spending time looking at a pasture full of stocker cattle with a client and largely discussing fly control issues. The evidence is stacked that summer has arrived.

Every year, once temperatures begin climbing over about 70 F, cattle begin showing signs of stress related to high temperatures, especially when being moved or handled. Many producers think of heat effects as isolated to the southern states or the southwest. Producers in many other parts of the US know otherwise. Temperatures in some places in the upper mid-west have already passed 100° F. Most areas of the country can be affected by elevated temperatures at some point in time or another. Certainly the northern parts of the country are not subject to heat as long as the south, plus there is a greater likelihood of temperatures dropping significantly at night, which alleviates the effect to some degree. Many producers also tend to think that heat affects only dairy or feedlot cattle. That is not true either. Beef cattle on pasture, young and mature alike are also affected by high temperatures. Animal and production losses represent millions of dollars not to mention the time and effort of dealing with the situation. This is true in all phases of the cattle industry.

High Temp Effects

Thermocomfort zone (TCZ) - this is the temperature range at which cattle are the most comfortable and thus do not use energy to cool their bodies (or heat them in cool temperatures). The TCZ for cattle will vary depending factors including:

body condition

hair coat color, length and

density

plane of nutrition

health

breed

age

acclimation

In general, cattle do not handle heat as well as humans. In a typical summer, cattle are generally less comfortable than humans at the same temperature. Cattle begin feeling the effects of the heat at 70° F or less if the humidity is high. This means producers should consider the fact that cattle are probably hot even when they (the producer) are not. Subsequently this may be affecting performance in some way.

In early stages of heat stress, the preliminary signs are not always readily noted. Feed and roughage intake may drop some but the animal may be fairly uncomfortable before this point. As cattle heat up and feed intake drops, cattle begin requiring additional energy, generally pulled from fat reserves, in order to help keep cool, thus reducing production and efficiency. Once this performance level drops it can be very difficult to recover. This is true in growing and feedlot cattle as well as in lactating females. It is also not uncommon for bulls to express depressed fertility levels.

In breeding cattle, a similar response is noted in terms of reduced nutrient or feed intake and overall energy metabolism in an effort to stay cool. Commonly the result is 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; essentially a double edged sword. This can support the case for summer supplementation and/or for use of an early spring or fall breeding.

Another area to monitor is immune response. This is a critical issue in newly-weaned cattle and those that are to be preconditioned and backgrounded. It becomes even more of a concern if these cattle are handled extensively and transported, particularly if they have been run through an auction facility 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 as well in most cases. We also know that under different types of stress, the body tends to deplete itself of critical nutrients such as zinc and copper, both vital to immune response. It has also been determined that under stress, the adrenal gland will produce steroid-like hormones that will essentially turn off the immune system. Yet another factor is that respiration rate (panting) is accelerated, increasing air flow through the respiratory tract, increasing the susceptibility to respiratory disease, especially under dusty conditions. Whatever the exact circumstance, heat stress is only one component in the overall physiological challenges these cattle encounter.

Three primary elements are critical in hot weather situations:

Intensity of heat

Duration

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. The Temperature-Humidity Index (THI) was developed to provide guidelines for critical temperatures and humidity levels. When the THI reaches 84 or more for two to three days in a row, steps need to be taken to help alleviate the heat. A copy of this chart may be found at http://cattletoday.com/archive/2004/July/CT343.shtml as part of an article discussing heat issues in cattle a few years ago.

Be Aware of the Signs of Heat Stress in Cattle

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:

Reduced grazing activity during normal grazing periods (early in the morning or evening).

Crowding under shade or around stock tanks. Remember that crowding intensifies the problem.

Panting and increased salivating.

Rapid breathing. Use the following as a gauge:

○ Moderate heat stress: 80 to 120 breaths per minute (bpm)

○ Strong heat stress: 120 to 160 bpm

○ Severe heat stress: over 160 bpm

Decreased or lack of normal movement

Reduced grazing activity during normal grazing periods.

Remember that since cattle do not perspire (sweat) well, they have to use the respiratory system to remove excess heat from their system. This is particularly true in heavily haired breeds. Brahman (Zebu) cattle are well known for generally being more heat tolerant than most English or Continental European. They have more highly developed sweat glands which gives them a greater capacity to sweat and thus dissipate heat. They also have more loose skin thus increasing evaporative capacity.

Having a Plan

A plan should be in place to help with weathering hot, humid periods and minimizing production losses. A heat management plan should be in place long before it gets warm. Some key components include:

1) Identify those cattle which are high risk. These include:

a) Newly arrived cattle that have experienced marketing stress.

b) Weaning or recently weaned cattle

c) Heavy fed, nearly finished and finished cattle, especially heifers.

d) Cattle that are grazing infested fescue pastures. Endophyte intake is well known to increase the body temperature of affected cattle.

e) Cattle that have been sick (respiratory) in the past and may have lung damage.

f) Black or dark-hided cattle.

g) Heavy bred cows - last trimester.

h) Older cows.

i) Thin cattle lacking energy stores.

High risk cattle should be placed in pastures, traps or pens which will help them reduce their heat loads as best possible. These pastures or pens should contain adequate shading and plenty of clean fresh water. In the feedyard, pens facing east or southeast have been shown to have the lowest radiant heat load and showed lower death losses. Avoid placing these types of cattle in pens or pastures with features that obstruct air flow. Areas next to irrigated crops should be avoided since this also increases the humidity in the air. Take measures to control flies since flies cause cattle to bunch which also restricts air flow.

2) Water Supply. Amazingly, every year cattle are lost because they are placed in areas with insufficient water. Some of this has been as a result of heavy drought affected areas where ponds have dried up and measures were not taken to provide adequate water rapidly enough. Drinking water is the most efficient and fastest way for cattle to reduce body temperature. At temperatures above 80° F, they may need in excess of two gallons per hour for each 100 lbs of body weight. Heavily lactating cows will require even more to maintain milk production. For a herd of 100 average sized cows (~1,100 lbs), 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! Availability of fresh, clean water has a direct effect on feed intake and subsequent energy intake. Additionally, cattle in a confined feeding situation need at least three inches of linear space at the waterers. Water has long been known as the single most important nutrient. This is especially true during the heat of the summer. Thought also needs to be given to a contingency plan in the event that something might interrupt the water supply. A final issue concerns water quality. Water provided in ponds heavy with silt or algae contamination (also common in drought conditions) 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 ion most cases and that intake is significantly higher from these sources.

3) Shade and Shade Structures. 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 shade for granted. In feedyards or growing operations research has shown that adequate shading can cut death loss in half. Shade also increases feed or nutrient intake. Shade should be from 7 to 14 feet off the ground and provide from 40 to 50 square feet per animal. In pastures with trees for shade, this number should be increased in order to prevent excessive grouping which may kill trees over time. It may be necessary to construct some additional shades in order to increase availability in pastures even when trees are available.

4) Handling and processing. DO NOT handle or process cattle in hot weather if at all possible. Research has shown that movement or handling of cattle during hot weather can increase body temperature from .5 to 3.5F. 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. Holding and processing areas should have shade and sprinklers available.

5) Sprinkler Systems. 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. Sprinkling cattle helps reduce body temperatures by increasing evaporative cooling. It can also help reduce ground temperature as well. Cattle need to be thoroughly wetted, not just misted. Research shows cattle under sprinklers gain faster and with increased feed efficiency. Sprinkling should take place intermittently over the course of the day to prevent the development of local high humidity levels.

6) Feeding and Supplementation. Hot weather often dictates a need for supplementation of pasture cattle since nutrient intakes will be depressed. Nutrient intake can only be maintained by feeding a more concentrated supplement to offset the reduction. For growing and finishing cattle it also makes sense to reduce energy levels. Ration energy level reduction will reduce fermentation and the associated heat production. This is typically done by reducing the grain concentration in the ration. During the hot months, however, it is often effective to reduce the grain and add back a pound or so of fat. Fat contains 2.25 times more energy than grain and can effectively replace the energy from grain. It is important that the fat level remain less than seven percent of the ration dry matter content to prevent interfering with fiber digestion in the rumen.

Conclusions

It is important to recognize that 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 will help producers effectively reduce heat stress in breeding, growing and finishing cattle. This will help 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 by phone at (903) 352-3475 by e-mail at sblez@verizon.net. Also, you can follow us on Facebook at www.facebook.com\reveillelivestockconcepts.







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