Heat Stress Already a Concern

Published on: 10:09AM Jun 13, 2011

In some areas, summertime arrived early as many are already dealing with high heat and humidity. Animals, cattle included, have difficulty regulating their body temperature during extreme heat.  There are some common sense things we can do to help them manage this problem. 

One of the most vital things to consider is water supply.  Consuming water is the quickest and most efficient method to reduce body temperature.  Water prevents dehydration and allows heat to be dissipated through evaporative cooling and urination.  Water sources should be kept clean and assessable to encourage water consumption. It is important to be sure there is sufficient space for all animals to drink.  Water tank space can vary greatly in management systems. 

In systems where the animals are a close distance to water and drink periodically, two feet of tank perimeter per head is usually adequate.  In range situations where the entire herd moves to water and drinks at one time much more space is needed.  Possibly up to two foot per head.  Storage capacity, low flow rates and unfamiliar taste can also have a negative impact on water consumption. Range systems should be able to supply the days supply in a four hour period and in a dry lot situation within an eight hour period.

This is a time of year that in parts of the country many cattle are processed for the summer. Internal (dewormers) and external (flytags) parasite control programs are often utilized during this season.

Processing timing should be planned to avoid weather stress events. Heat stress is a very real event which decreases the animal’s ability to respond to vaccines or compensate for other stresses such as processing or disease challenges. In warm weather, both temperature and humidity levels should be evaluated and cattle working should be avoided when the Temperature Humidity Index is 80 or above. Cattle do not cool down immediately after a hot day; it may take up to 6 hours for heat dissipation to occur. Thus, cattle worked at the end of the day or immediately after sunset may still incur large amounts of heat stress. 

During the hot times of the year, early morning is optimal for working the cattle because we have had the maximum time of heat dissipation overnight.  Try to complete processing before it begins to get hot again in the morning (by 8-9 am).

To add even further to the issue of heat is the issue of fescue. Fescue is both a blessing and a curse. Cattle grazing endophyte infected tall fescue may present a variety of symptoms associated with the toxic principles in the endophyte (a fungus that is not visible to the naked eye, but lives within the grass).  Visible signs in the cattle may include failure to shed their winter coat in summer, shaggy appearance, or sloughing of tail or hooves in winter.   Many of the signs of toxicosis may be harder to see and include peripheral vasoconstriction (narrowing of blood vessels reducing blood flow to extremities), high body temperature, increased respiration rate (a cooling mechanism for the cattle), reduced forage intake, and decreased weight gains.  In breeding herds, fescue toxicosis may present as a reproductive disorder by contributing to low pregnancy rates. 

Tall fescue toxicosis is responsible for the “summer slump” sometimes noted in growing calves grazing on pasture.  The increased body temperature causes animals to seek shade and frequently stand in the ponds or creeks.  Management suggestions for dealing with stands of toxic tall fescue include: dilution, grass management and animal movement.  Stands of tall fescue can be diluted by interseeding legumes (clovers and lespedeza) and other grasses or supplementing cattle with other sources of nutrition at specific times of year.  The dilution of the toxin through other feedstuffs diminishes the signs of toxicity in the animals.

Proper grass management is important because the alkaloid levels are highest when the seedheads are present.  If you can keep the fescue in a vegetative state for as long as possible, then remove the animals when the grass goes to seed, you will minimize the impact of this syndrome.  Clipping pastures also helps because it removes the toxic seedheads and the top of the grass canopy, permitting legumes to receive the much needed sunlight to grow. 

Like people cattle do not like to eat in the heat of the day. Changing feeding patterns may be an option. This is especially useful for cattle that are not in a pasture setting.  Feeding 2 -4 four hours after the peak ambient temperature may help keep consumption more regular.

Lastly it is often desirable to provide shade. There are two things to be aware of when provided shade to heat stressed animals. If the area provided is not large enough the animals will congregate and can increase their body temperatures more than if there was not shade.  Secondly, airflow is important. Shade needs to be provided in a manner to improve or, at the very least, not hinder airflow.

The heat of summer is unavoidable but steps can be taken to minimize the negative consequences. Remember to use good common sense to keep animals as comfortable as possible.