The excellent insulating properties of feathers and the almost complete absence of sweat glands in the skin limit the loss of heat. Insulation is essential for small birds and mammals when the temperature of the environment is well below that of their bodies, because the heat lost is proportional to the surface area of the bird: thus, the smaller the creature, the higher the ratio of the surface area to its body weight. Large birds lose much less heat by radiation. When the surrounding temperature is high, the amount of heat transferred from the body to the outside air is less than when the temperature is low. If the air temperature approaches the bird's blood temperature, no heat is lost at all because there is no longer a difference in temperature between the bird and the outside air. A bird can still lose heat even when the air temperature is higher than that of its body: this happens when the air is dry. The heat loss under these circumstances is purely by the cooling effect of evaporation. If the air is humid, however, evaporation is slower and it may be insufficient to keep the bird's temperature down to a safe level. If it rises too high, the bird suffers discomfort which can lead to collapse and death. In warm and humid climates it is therefore necessary to provide not only adequate shade, but to avoid stuffy buildings with high humidity. Moving air helps cooling, especially if the bird can wet itself in a bath. In addition to the heat lost by radiation, the bird also loses warmth in the air it breathes out, which has been previously warmed by passage through the lungs and air-sacs.
When the bird gets excessively hot, it pants and gapes. This uses up more energy and causes therefore an increased heat output. The bird also fluffs its feathers until they separate from one another, exposing the skin and facilitating heat loss by convection. The wings are held half-extended, drooping on the floor. If eventually the bird cannot lose sufficient heat, it becomes comatosed, sometimes with brief terminal convulsions. Its temperature may rise by 6°F (3°C) or more before death occurs. Housing birds in hot weather in exposed wooden buildings without insulation and good ceiling space is liable to produce heatstroke unless there is a wide area of wire netting in front of the bird-house to permit a flow of air.
Immediate treatment consists of removing distressed birds to an air-conditioned room or spraying them periodically with cold water. Recovery is usually rapid, provided that body temperature has not risen too far. Birds which have been subjected to heatstroke may, however, be off-colour for a day or so and may afterwards be more prone to infections, particularly respiratory diseases.
Chilling or Hypothermia:
The term "chilling" has been given to many undiagnosed illnesses in birds, mammals and man. True chilling is a stress syndrome in which the vitality of the tissues particularly that of the lungs is lowered, making them more susecptible to infections and other injurious agents. A severe fall in the temperature of the environment is one factor, but sudden starvation, shock, injury or exhaustion may affect the adrenal cortex and cause lessening of the body's resistance. Chilling from actual cold is liable to occur mainly in newly imported tropical birds or birds undergoing a heavy moult. The most extreme examples of the former type of chilling have been known to happen when birds are imported by air in crates in unheated compartments at 15-30,000 ft. from Asia, Africa or other tropical countries. Under these conditions the temperature in the freight hold drops well below freezing even in summer. The birds have no water, and the resulting stress on them is extreme. On arrival at their destination, such birds are usually comatose, with a body temperature often registering below the scale of the thermometer. Placing the birds in an environment of 90-95°F (30-33°C) quickly enlivens the majority, but a proportion will slowly die. Those which recover show for a time an almost obsessional thirst. During the subsequent days or weeks a steady number of survivors will continue to develop signs of various affections, it being essential to watch them closely so that appropriate treatment may be given without delay.
Hypothermia can also occur in acclimatised birds in temperate and cooler countries when their body heat is lowered as the result of insufficient or unsuitable feeding, extensive injury or major surgery, sudden heavy moult, oil contamination causing matting of the feathers, and wetting of the skin after the plumage has been washed with detergents. The mechanisms involved can only be reconstructed approximately by analogy with similar processes in mammals, but it is believed that a breakdown occurs in the control of blood sugar, liver and muscle glycogen levels as well as the levels of sodium, potassium, calcium, magnesium, phosphates, chlorides and other mineral ions in the blood and tissue fluids. The effect on pancreatic (insulin), adrenalin and histamine pro- duction is not known accurately.
Shock is a process which is little understood, but of which everyone is aware. Research on it is constantly being carried out both in man and animals, although to only a limited extent in poultry and other birds. Knowledge of the complex mechanisms involved and even the definition of shock are constantly having to be revised. Shock can be briefly defined as a depressive response to various stresses. Various types of shock are catalogued according to the cause, the system, the part of the body affected, the degree, the appearance, and the timing.
Examples include the following:
Cause: Crushing, compressive, decompressive, haemorrhagic, electric, toxic, anaphylactic and surgical factors.
System or region: Neurological shock, causing pain due to marked nervous involvement.
Degree: Mild, severe.
Appearance of main clinical signs: Depressive or torpid, excitable or erethismic.
Timing: Primary, secondary, delayed or recurring shock.
Haemorrhagic shock is of particular importance and usually comes as a sequel to accidental or surgical injury. In old parrots and other species which live to a great age in captivity, haemorrhagic shock may occur spontaneously during a burst of activity after injury, being usually associated with degenerative vascular or heart disease. After stemming the visible external haemorrhage, subcutaneous injections of small quantities of hypo or isotonic saline should be made at various sites in quantities of up to 20 ml. per kg. of the bird's weight. The bird must not be made too warm unless its temperature is obviously low to the touch: 70-85°F--approximately 20--40°C--is recommended according to response.
Idiosyncracy and other Sensitivities:
The part played by the phenomena described below, especially allergy, has been shown in recent years to be more far-reaching than was previously believed. The study of the nature, the production, and the action of antibodies and the antigens, or allergens which stimulate the reaction is known as immunology. Whether pathogenic microorganisms succeed in entering the body is largely controlled by the degree of immunity it has built up. Antibodies assist in the resistance to disease, and in the tolerance or rejection of grafts of tissues and whole organs to replace the diseased ones. The violent responses shown by the skin of some individuals or their internal organs to eating, inhaling or merely touching certain substances, and the occasional illness produced by blood transfusions or serum injections are all due to the production of antibodies. A study of immunology explains how disease is produced and why an agent can cause illness in one individual but not in another.
This is the exaggerated response shown by certain individuals, strains, or even species to contact, or entry into the body of a small quantity of certain foreign substances. From the first occasion on which the body cells meet this substance the response is there: the individual possesses this peculiar reaction from birth. An example of idiosyncrasy in many species of birds is the violent shock reaction and death which follows an injection of even low doses of streptomycin, when other species like mammals of equal size, would show no undesirable effects. An idiosyncratic tolerance or intolerance to barbiturate anaesthetic has been noted in individual men and certain Other mammals. A dose which safely anaesthetises the vast majority of dogs or cats may kill one individual and yet leaye another fully conscious. Idiosyncrasy is probably therefore the result of a congenital or hereditary peculiarity of metabolism, which only shows itself on the first challenge by the rejected substance.
Allergy is a much over-used word. People are heard to say that someone is allergic to certain people, when what is meant is merely that he dislikes them. Allergy is really a local response by tissues to the presence of a foreign substance at the second or a subsequent challenge. Allergic responses are virtually unrecorded in birds. To be allergic a bird must meet and be sensitized by the allergen or allergy-creating substance--usually a protein. When it meets the same substance, whether it be two weeks or even two years later, its tissues react violently with an allergic response. It is therefore an acquired response and is in fact a protective mechanism designed to repel invaders by building up a defensive armament. Unfortunately, the tissue reaction is not always beneficial to the health of the individual in question, and may result in local oedema, pain, shock or even cell death. The challenging foreign substances, which are usually large molecules like proteins and groups of sugars (polysaccharides), may be encountered by being swallowed, inhaled or merely through contact with the skin. Especially in man, such responses as dizziness, asthma, hay-fever, capillary haemorrhage of the skin, nettle rash, diarrhoea or vomiting may result when the second and later challenge occur. The amount of allergen required to produce these local effects need only be very small. When damaged by allergen-antibody reactions certain cells liberate a substance called histamine, which produces pain, swelling and some signs of shock.
Allergic skin, gut or respiratory reactions must not be confused with the response to irritant and poisonous substances. These have a specific chemical reaction of their own and produce similar skin or mucous membrane damage in most species of birds or mammals. Only the degree of reaction may differ a little. True allergic reactions usually affect only a few individuals within a species. Allergies to milk, egg, horse meat, various fish, carpet dyes, grass or other vegetation, wool and very many other substances, have been found in mammals. Information regarding avian allergies, however, is almost non-existent, although oedema of the glottis and marked swelling of the fleshy head structures of pigeons and poultry have been observed following mosquito bites. In the absence of obvious causes, such lesions have been assumed to be an allergic response to inhalation or ingestion of various allergens. Antihistamine or cortisone-like drugs are most likely to be helpful in the treatment of rare cases.
More profound reactions by tissues of the body leading to severe shock and death are called "anaphylaxis" or anaphylactic shock. This is a violent and sudden response of an allergic type which is not limited only to those cells and tissues in contact with the allergen entering the body. The whole defence mechanism, geared for action by the first challenge, is let loose in the second Or later challenges. In man and animals the second injection of serum (for example, an anti-tetanus inoculation) has caused some violent anaphylactic reactions. Sera containing antibodies to specific infectious diseases have been little used in cage birds, and even then this has been mainly experimental. It is probable that with increasing knowledge of avian disease this practice will increase and anaphylactic responses to serum will become more important. Corticosteroid drugs and antihistamines are most useful for lessening anaphylactic shock.
Many so-called allergies are not allergies at all but hypersensitivities. For instance, many avian species react violently when injected with low therapeutic doses of streptomycin, dihydrostreptomycin, chloramphenicol and numerous other drugs they have never previously encountered. Signs of violent shock, collapse, coma and death usually result. The skin in such an instance is unaffected, though it may just be detectable that it has become paler than usual. Hypersensitivity is merely an exaggerated response in an individual to a dose of foreign substance which produces in the majority a normal or therapeutic response or even no response at all. It is a useful term for a state which includes idiosyncracy, allergy and anaphylaxis, until the precise cause of the reaction and its mechanism can be elucidated and named. Fleas and other ectoparasites produce such responses in both mammals and birds, and it is safest to refer to the abnormal response elicited as a "hypersensitive reaction". Although experimental proof is lacking, it is quite possible that the bird which is constantly pecking at its skin or plucking feathers, wheezing, having loose droppings or showing necrosis of the feet, or other complaints, may be suffering from the result of allergic or other hypersensitive reactions to food or materials found in its cage. This is partly why radical changes in diet, environment and management are advocated in this book for several diseases where the cause is unknown.
The reasons for any improvement can then be found by replacing the changed circumstances one by one until the same clinical signs of disease return. Relief of oedematous swellings, laboured, wheezy breathing and other signs can be temporarily relieved by corticosteroid drugs and to some extent by antihistamines.
Photosensitivity is an exaggerated response to light, especially to sun or ultraviolet light. The response is a reddening of the skin which may progress to severe sunburn. White-haired mammals and possibly white-feathered birds appear to be most prone. Such birds should be removed to an environment of subdued light and exposed only gradually again to sunlight.
This is an induced tendency to light sensitivity, which occurs as a result of eating certain plants or the administering of certain drugs. In cattle for example, the plants St. John's Wort (Hypericurn spp.), kale and rape (Brassica spp.), as well as some sulphonamides and tetracyclines derange the metabolism to such an extent that the normal tolerance of the skin to certain wavelengths of light is lost and burns result. No proven cases, however, have yet been reported in cage birds.
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Hamilton & District Budgerigar Society Inc.