Heat Stress in Animals: Causes, Treatment and Prevention

Heat stress is a form of hyperthermia (elevated body temperature) in which, the physiological systems of the body fail to regulate the body temperature within a normal range. Heat stress in animals is considered to be violation of animal welfare and rights. It may not be due to elevated environmental temperature as the only culprit, but it may be due to a combined effect of environmental temperature and relative humidity. The aftermath of heat stroke may lead to severe damages in terms of general health, immunity and productivity of farm animals e.g. poultry, dairy and meat animals; pets e.g. dogs, cats, exotic birds, psittacine, rabbits etc. and work animals e.g. equines, camels, draught animals, etc.

Animals may be prone to heat stress due to higher environmental Temperature-Humidity Index (THI), solar radiation and lower wind speed in summer season. Heat exhaustion may be attributed to several etiologies occurring singly or in multifactorial forms. Environmental factors like:

(i) Recent rainfall and subsequent rise in humidity leading to decreased sweating and breathing for heat dissipation.

(ii) A high ongoing minimum and maximum circulating temperature and or high environmental humidity.

(iii) A high solar radiation level due to absence of natural cloud cover may predispose animals to heat stroke.

(iv) Extended period (> 5 days) having minimal air circulation leading to consistently harsh environment.

(v) Warm cloudy nights might also increase the risk of heat stroke as the animals dissipate the heat energy during night.

(vi) A sudden shift to adverse climatic conditions might also predispose animals to heat stress.

(vii) Husbandry practices and farm layout may sometimes facilitate the onset of heat stress in animals.

Some characteristics of animals might put the individual to a greater risk of heat stroke. Following attributes might be responsible for higher incidence of heat stroke in conjunction with some environmental factors:

(i) Breed: Indigenous breeds (Bos indicus e.g. Sahiwal) are more heat tolerant than exotic breeds (Bos Taurus e.g. Ayrshire). Similarly, Brachycephalic anatomy (flat-faced breeds) such as Pugs, English bulldogs, French bulldogs, Persian and Himalayan cats are among other breeds which are not heat tolerant.

(ii) Genetic variation: Variations attributable to the phenotypes of individual animal breeds.

(iii) Coat color and type: Animals with lighter coat color (e.g. cattle vs buffalo) tend to be more tolerant of heat. Animals having coarse hair type as coat may be more prone to heat stress (e.g. sheep vs goat).

(iv) Body condition: Obese and emaciated animals tend to be more susceptible to heat stroke.

(v) Age: Animals that are recently weaned or aged animals are more prone to heat stress.

(vi) Adaptation: Indigenous animals might adapt to local climatic conditions, provided the temperature change is gradual.

(vii) Disease: Animals having ailment of any etiology might not be able to adapt to changes in the weather.

(viii) Physiological State: Lactating animals or peri-parturient animals might be at higher risks of getting affected by temperature or humidity rise due to their hormonal profiles.

(ix) Vector Density: Some flies and mosquitoes might cause nuisance to animals, leading to overcrowding/ huddling towards vector free areas.

Increased breathing, heart and sweating rates may be recorded. Initially, symptoms like increased panting, hypersalivation, gastrointestinal problems (vomiting, diarrhea) might be noticeable. Behavioral changes like seeking shade, crowding towards shady areas, orientation avoiding contact with solar radiation, standing in or next to water source might be observed in animals having onset of heat stroke. Productivity parameters like milk production, egg production, weight gain, FCR (feed conversion rate), milk and meat composition (decline in protein and fat contents) might show abrupt changes in heat stressed animals. Drop in routine feed consumption and sudden increase in water intake might signal the onset of heat stress. The later stages of heat stressed animals might exhibit symptoms like dry and hyper congested mucosal surfaces (epistaxis might be seen in cats), listlessness/lethargy, staggered gait, general weakness and electrolyte loss from the body. Neurological symptoms might include irritability, delusions, hallucinations, seizures and coma.

Heat stress might cause serious damage to muscles/ internal organs of affected animals, indicating the need for emergency medical care. Animals should be made to move away from direct sunlight to cool area. The continuous application of cool water therapy is highly indicated to manage a heat stressed animal. Treatment goal is to manage the hyperthermia, provide cardiovascular support and to prevent complications associated with hyperthermia. Fluid, electrolyte and Vitamin C therapy could be applied to counteract the ill effects of heat stroke especially in farm animals e.g poultry. The intravenous (i/v) corticosteroid therapy may help reduce myocardial stress. Anti-microbial therapy may be indicated to reduce chances of secondary infection

The incidence of heat stress in animals might be reduced largely if there is a beforehand management of cases. The following approaches might be helpful in preventing heat stroke cases in dairy, meat, working, pets and zoo animals:

It is impossible to control the environmental variations in temperature, humidity and wind circulation to counter heat stroke cases in open areas. Therefore, the cases might be reduced by appropriate farm layout, close monitoring, adopting appropriate preventive measures, adequate management and planning before the onset of environmental temperature and humidity rise.