Breaching Heat Stress Comfort Zones
Have you ever noticed your goats lying on their sides more than usual on a hot day? Do they hang out in the barn or under a tree all day and pant? These are some of the ways goats cope with heat stress. Lying flat out, they also expose more body surface area, especially the short-haired parts of the body. They seek shade. When it gets hotter, involuntary functions kick into high gear.
The Hot Zone
The comfort zone for goats is between 32-86o F. Above 86o F, goats may begin to experience mild heat stress, especially when humidity cranks up the heat index. As heat and humidity climb, goats can have serious problems with thermal stress.
High temperatures affect body function in many ways. The hypothalamus, lying at the base of the brain, is in charge of balancing the body's heat loss and gain by regulating respiration, skin temperature, sweating and muscle tone. Goats get eight times more relief from the heat by panting than by sweating, so rapid breathing is their primary form of cooling themselves. Panting and collapse are the most obvious signs of heat stress, and the rectal temperature will exceed 104o F.
When the weather warms up, animals eat less in an involuntary effort to reduce body heat feed and water consumption go down. Animals may also reduce water intake, however they need water to help keep them cooler.
It is well documented that certain animals are best suited to certain environments. Pygmy goats evolved in the tropics, but they seem to adapt well to almost any environment. They are well suited to warmer climates, and you can see that by understanding their body shape and color. Excess skin, in this case the large barrel, increases the surface area in relation to body size to enhance evaporative cooling. Of course, the barrel is probably not as large in the summer because the rumen is not as full as it is in cooler weather - ruminant appetites decreases when the weather warms up.
Goat breeds with floppy ears, loose skin, longer hair, and those with horns, should also be more heat tolerant. Long ears and loose skin represent increased surface area. But, long hair? Yes, its purpose is to protect the skin by preventing sun rays from reaching the skin. It also insulates and provides a buffer zone between body temperature and the environment. Just ask Angora goats before shearing time in July and August!
Goats and other ruminants have a unique network of blood vessels at the base of the brain, called the rete mirabile, that may help diffuse body heat in order to keep the brain slightly cooler than the rest of the body.
Coat and skin colors give protection from the sun. Light-colored coats reflect the most light and heat, and dark coats absorb the most. You'd think that skin color would serve the same purpose, but it doesn't. Dark skin is the most protective against the sun's harmful radiation. (Melanin pigmentation provides protection against UV damage that causes skin cancer.)
Problems Can Arise When...
Weather and other factors can combine to get any goat, but some are more susceptible to overheating. Overweight goats cannot exchange heat efficiently. Overcrowded animals exert themselves due to fighting and increased competition for resources. Aged goats just don't function as well as they used to, and the very young have yet to reach optimum function. Animals in poor health (illness or parasites) may not be able to cope with this added burden. Selenium deficiency may exacerbate heat stress due to marginal muscle tone. Unventilated confinement, such as being locked in a poorly ventilated barn, crate or vehicle, can be a serious threat to an animal's life in a very short time.
Breeding is too strenuous an activity during hot weather. In fact, bucks should be housed a respectable distance from does in heat, lest they overexert along the fence line or remain in the sun for prolonged periods. Any forced exertion should be avoided. Don't pick a hot, humid day to trim hooves or give the goats any other hassles.
Hot days and an occasionally cool night may create digestive upsets due to several days of minimal food consumption followed by a cool night of eating to excess. Abnormal feeding patterns may lead to unusual problems, like polioencephalomalacia or founder. High humidity may lead to pneumonia or aggravate the lungs of goats who have had lung damage from previous bouts.
If It Happens
A veterinarian should be consulted as soon as you see signs of heat stress. The animal may experience pain and swelling, and your vet may prescribe drugs to treat these symptoms. There may be a variety of moderate to severe blood abnormalities, impaired kidney function and metabolic acidosis. Electrolyte imbalances are common in heat stress, and IV liquids may need to be administered to combat acidosis. Tissue destruction begins prior to death, so prompt medical attention is imperative.
Act promptly when you find a goat you expect is suffering from heat stroke. If the goat can walk, isolate it in the shade and take its temperature. If the temperature is over 105o F, set a fan for direct ventilation, spray the coat with water, and wet the head, legs and stomach with water. (Cold water may be too great a temperature shock to the vascular system - any water will do. If the symptoms diminish in 15-20 minutes, the goat may continue recovery on its own. Make sure the temperature is reduced to 102.5o F, and watch the goat closely for a few hours to see that it acts normally. Continue to monitor its behavior, temperature, pulse and respiration after the animal has been stabilized.
If the goat is prostrate and unable to walk, do not move it. Take its temperature. Erect shade if the animal is in direct sunlight and begin cooling with water. You will need the vet. When cooling therapy reduces the goat's rectal temperature to 102.5o F, cooling measures can be discontinued.
There are a number of measures you can take to prevent most cases of thermal stress. Reduce the quality of the hay you are feeding, and reduce or discontinue grain rations. Give free access to clean, cool water and freshen it frequently. Move the water source into the barn if your goats normally have to travel to reach it. Make loose trace-mineral salt available at all times to aid water consumption. Provide shade through the daylight hours. Ventilate barns with natural convection currents (doors, windows and roof vents). Electric fans (closed motor fans are the safest) and misting systems also help evaporative heat loss. (Be careful that the goats cannot reach electrical cords.) Provide adequate barn and feeder space to reduce competition for resources.
Barns can be kept cooler by installing roofing to reflect sunlight and painting existing outside walls light colors. Cool the barn roof with a water sprinkler, making sure the runoff is diverted and does not add to the humidity level in the barn.
In areas of the country where hot, humid weather is a routine occurrence, your county extension service can probably give excellent suggestions about barn design and fan/sprinkler cooling systems.
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