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HEAT STRESS


COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992

Extension Goat Handbook

This material was contributed from collections at the National Agricultural Library. However, users should direct all inquires about the contents to authors or originating agencies.

DOCN 000000054
NO F-11
HEAT STRESS
J. D. Roussel; Louisiana State U., Baton Rouge
L. J. Hutchinson; Pennsylvania State U., University Park
Anatomy and Physiology

1 Nearly every life form is affected in some way by high temperatures, and goats are no exception. It is not heat alone that causes stress to the goat; but it is the combination of temperature and humidity when some crucial limit has been reached, which shuts down all bodily functions other than those critical for survival.

2 Water and Feed Intake The most immediate impact of heat stress can be seen in changes of water and feed comsumption. As the temperature rises, so does the animal's need for water. Plenty of water should be provided, free-choice, at all times. However, if water becomes scarce, goats hold an advantage over other domestic non-desert species in that they are better adapted to utilize the water content of feeds. However, rising temperatures also tend to reduce voluntary feed intake. This is the result of an attempt by the animal to reduce the production of body heat especially from fibrous feeds, lower physical activity, seek shade and change grazing to night hours.

3 Nutrition and Reproduction A long range result of diminished nutrition due to heat stress is a reduced kid crop. If the doe is pregnant, especially near the end of gestation, this heat induced lack of proper nutrition may result in literal starvation of the fetus. On the other hand, if the doe is not pregnant, an insufficient supply of energy due to heat stress will cause absence of follicular development. The same is true for the buck in terms of sperm production. Extremes in heat can affect reproduction directly as well, through 1) sperm and ova degeneration within the reproductive tract, 2) creation of hormone imbalances via action of the hypothalamus, and 3) suppression of libido and the physical act of mating.

4 Removal of Body Heat In order to keep such drastic events from occur ring, three major physical processes exist by which heat can be dissipated. They are:
1) convection
2) conduction, and
3) radiation cooling.
Convection cooling occurs when an air stream passes over the body either by wind or b ++++MISSING DATA++++

5 Hair Coat Fortunately, the goat has it's own line of defense when environmental temperatures exceed body temperature. The first means of protection is provided by the coat, both from it's color and physical characteristics. The principle behind coat color involves the reflection of sun rays. It has been documented that white coats provide maximum protection against radiant heat and black coats give minimum protection, with variations falling in between. Reflective protection can be provided through physical characteristics of the coat as well. Contrary to popular opinion, long hair which lies close to the body is desirable. In this way, the coat acts as a mat to physically prevent the sun rays from reaching the animal's body. In addition, long hair serves as an insulator from the heat, providing an air buffer zone between the outer environment and the animal's body.

6 Skin Color The next line of protection is the skin. Color of the skin is important, except this time darker colors are preferred. The function of the darker skin is to absorb any ultraviolet light which may have penetrated the coat, thereby preventing damage to tissue proteins. Having an excess of skin has also been implicated as providing heat relief. It is believed that this excess skin serves to increase the surface area in relation to body size in order to enhance evaporation. This has been the explanation used in order to account for the large, floppy ears found on goats and other tropical animals. Horns have also been suggested as providing benefit by providing an area where blood can be cooled before reaching the brain. Certainly, the little understood rete of goats is in this connection a unique anatomical structure designed to keep the brain of goats cooler than the rest of the body.

7 Sweating and Respiration The greatest form of relief for the animal comes as the result of two seemingly contrasting forces: 1) water evaporation, and 2) water conservation. Water evaporation provides a direct form of relief as the result of two principle forces: 1) sweating, and 2) respiration. Sweating serves to cool the surface, but though it does provide some relief, respiration has been found to have eight times more evaporative capacity, thereby rendering it the chief form of relief from hot temperatures.

8 Water conservation on the other hand, plays a more indirect, but equally important role in the ability to tolerate heat. This function becomes extremely important if evaporative cooling is to occur when water supplies are scarce or nonexistant, otherwise dehydration will occur. Water conservation occurs chiefly through reduced renal and fecal excretion, and is facilitated by low potassium, high sodium excretion.

9 Methods of Heat Relief If the goat continues to suffer from heat, even with all of these forms of protection, then it becomes the producer's responsibility
++++MISSING DATA++++
1) non-metalic reflecting
2) non-metalic non-reflecting
3) metalic reflecting, and
4) metalic non-reflecting.

10 When keeping animals in confinement, costs are expected to be higher. The most expensive yet most beneficial method of relief is provided by airconditioning. Of course, this investment is usually economically questionable. In order to reduce such costs, experiments have tried to determine if air-conditioning of just the head might provide relief. However, cooling the head or sprinkling with water provided little benefit. Instead, it was best to ensure a roof for protection from the sun, that air be allowed to circulate under the roof and that the roof was sun reflecting or cooled with a water sprinkler.

11 A long range means of increasing heat tolerance can be accomplished through genetic selection. It is important not to select for individual characteristics, i.e. ear length, but rather for a general over-all tolerance coupled with the capacity to produce milk. Once those individuals have been selected, additional benefits can be gained by cross-breeding to take advantage of hybrid vigor. Studies are needed to determine the truth behind general opinions that Nubians are more heat-tolerant, -although many are found in Canada; and Saanen are less suited in tropical countries, -although they have made some outstanding contributions in some tropical countries including Israel and Australia, and in crossbreeding in developing countries. Certainly, possible differences between dry and humid tropics for dairy goats must be delineated, but certain Carribean experiences, for example, are very encouraging. The specific dynamic action of some feed nutrients (e.g. protein and fiber) and the remarkable studies of desert zoologists must be utilized by dairy goat practitioners, since it is now known that some goats need water no more often than every four days and survive very well and produce sufficient milk to raise one to two kids.

HEAT STRESS
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992


 
 


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