Vet´s perspective

Jul 8, 2011
by WLJ

Heat stress—problems and prevention

Increased ambient temperatures this summer should raise producer awareness of heat stress conditions affecting their livestock and pets. Heat stroke is a condition resulting from an increased body temperature. Animals that have been exposed to heat stress for a prolonged period of time may eventually exhibit organ abnormalities associated with severe dehydration and shock. Humidity levels also play a big part in this condition; thus, the heat index (both temperature and humidity levels) is the most accurate measurement of heat stress.

Tolerance levels between species vary in degree. Cattle and camellids tend to be more affected by increased temperatures than smaller ruminants such as sheep and goats. Darker-colored animals may be more susceptible to heat stress, whereas lighter-colored animals are often more prone to sunburn. Very young and immunocompromised animals are also at a higher risk for illness due to extreme changes in temperature. Besides dehydration, animals are more susceptible to pneumonia and parasitic diseases in general.

Clinical signs of heat stress can be variable, but animals often will exhibit the following: panting, rapid breathing, weakness and inability to stand, and elevated rectal temperatures. A rectal temperature over 107 degrees Fahrenheit can cause cellu lar damage in an animal’s organ systems and death may occur without proper cooling and treatment.

Animals demonstrating heat stress should be moved to a shaded environment and have the body temperature gradually cooled to normal limits. Besides applying water to the animal’s skin, one may also try patting rubbing alcohol along areas between the legs and on the underside of the belly. It is contraindicated to apply water to animals with wool (such as sheep or camellids with heavy fiber) because air will not be able to pass through the wet fleece or fiber and create a cooling effect. Although offering water is essential, severely affected animals can often benefit from fluids administered in the vein or under the skin; your veterinarian would be happy to assist with these measures of treatment.

Heat stress can have lasting effects on the performance and profitability of your herd in the long-term. Signs of heat stress in your herd may be demonstrated as: reduced feed intake, reduced fertility and activity, increased respiratory rate, and shade or shelter-seeking behavior. Breeding-aged males that undergo episodes of heat stress may require up to two months of recovery before semen is adequate for fertilization. Before heat stress situations are reached, a control and treatment protocol should be in place. The following advice can help minimize detrimental effects to your herd and aid in maintaining efficiency and performance.

First, ensure that fresh water is always available to animals—their needs will increase dramatically during hot summer months. It is not unusual during heat stress for animals to drink five times the amount of water they normally would. Animals that are being fed additional grain or forage should receive their rations early in the morning, or before dusk, when the environmental temperature is cooler.

Cattle (and other animals) will typically decrease their feed intake during the hottest times of the day. This is the body’s natural response to preventing the additional rise in body core temperature (thus production of more heat) due to digestion of meals. Rations with nutrient-dense formulations are usually preferred during periods of high heat and stress so that animals may keep their digestion and body conditions in maintenance and growing condition. Conversely, as temperatures begin to decrease, herd managers should be monitoring animals for signs of bloat and acidosis—as animals often will increase their dietary consumption rapidly.

Younger animals especially require more water on a percent body weight basis simply because more of the body mass is made up of water and they have a more rapid metabolism. Juveniles will drink less water at a time, but overall drink more times per a day than their elders.

Solutions can be added to watering tanks in order to replenish electrolytes that are lost due to sweating, panting and urination. Electrolytes are chemical ions that help keep the body’s fluid balance in order, as well as acting as a co-factor in several systemic processes.

Some disagreement centers on the need for shade in grazing operations, but many studies have shown benefits to shade. Not only is animal welfare greatly improved, but shade access also can improve weight gain, milk production, and reproductive parameters.

Shaded areas should be available for cattle to congregate during the increased temperatures of high-noon and to minimize direct contact with the sun. Livestock shelters do not have to be complicated or elaborate by any means, but should be large enough to house several members of the herd at any given time. Large, mature trees are often a costeffective alternative chosen by ranchers. Other options include calf hutches, carports, and three-sided pole sheds. Shelters that can be portable make moving easy for rotational-grazing systems.

If animals are housed continuously, ventilation and air quality are key factors to maintaining herd health. Some producers will have cool water sprayers that activate periodically throughout the day to reduce heat stress.

Finally, for both your animals’ sake as well as your own, transportation and herd work should be conducted on cooler days or during dawn and dusk if possible. — Dr. Genevieve Grammer [Dr. Genevieve Grammer is a mixed-species veterinarian practicing at Calhan Veterinary Clinic in Calhan, CO.