The Pituitary Gland:
This gland lies on the underside of the brain, roughly in the centre of the floor of the cranium. It is given its common name of "master gland" because it largely controls all the other ductless glands. It may be damaged by infection, over-stimulation or the growth of tumors. It is so complex and so inaccessible surgically that any derangement will almost inevitably prove fatal. A diseased pituitary gland causes abnormal development in a young chick. Growth may be either slowed or quickened and parts of the body may grow at different rates, producing monstrosities. In the grown bird anatomical proportions are unlikely to alter greatly, but metabolism is either stimulated or retarded. Tumor formation involving overgrowth of true glandular tissue will stimulate, while non-glandular tumors will tend to replace the gland and lessen pituitary hormone output. Because of the complex nature of the chemical products produced by the pituitary, and because of the fact that most of these chemicals act indirectly on body tissue by stimulating or suppressing the output of other glands, the ensuing diseases are numerous and variable.
The result of a diseased pituitary gland for example may be a stunted, nervous bird, or a sluggish, obese balding one. Interference with water and mineral metabolism may result in increased thirst. Resistance to shock or infections may be lowered in some cases and some birds may show abnormal sexual behavior or sex reversal. In Britain, tumors of the pituitary gland have so far figured among the rare avian tumors, but in North America some surveys have shown them to be among the commonest types in budgerigars. Some pituitary affections of birds are possibly manifested by a proportion of the dead-in-the-shell and newly hatched monsters, so commonly met by budgerigar breeders.
The Thyroid Gland:
This gland is situated astride the syrinx at the lower end of the windpipe or trachea and lies at varying distances inside the thorax according to species. In most it is only a short way behind the clavicles. Its main function in the young is to influence the growth rate. In the adult, after growth is completed, the gland "goes into low gear" but continues to control the metabolic rate. When the thyroid gland is overactive, development is rapid, but since bodily activity is also over-stimulated, weight increase is less than normal. Precocity results, including sexual precocity and premature aging. When the gland is under-active, development is slow and a weak, retarded bird results. In severe cases, the bird cannot fend for itself; it is even unable to find food and usually starves to death at an early age. If the thyroid becomes under-active in an adult, the main changes are increase of weight due to deposition of fat, loss of activity and a partial molt with poor feathering and lethargy. The slowing of many bodily functions may also be apparent, together with the excretion of small, constipated droppings, a fall in body temperature and slower heart and respiratory rates.
Not all fat birds show clear-cut thyroid changes and thyroid enlargements and tumors are not confined to obese birds. The proportion of birds with both abnormalities, however, is too great merely to be ascribed to coincidence. Overweight almost always decreases with progressive thyroid enlargement; consequently by the time obvious swellings and digestive and respiratory embarrassments are apparent, the bird is generally normal in weight or thin, weak and lifeless. Sometimes such birds may give the impression of being fat due to fluffing-up of the feathers. One indication of a previously obese bird is the coarseness and pinkish-yellow coloration of the skin, especially of the undersurface where it hangs in limp folds below the lower throat, breast and abdomen. When over-activity of the thyroid develops in an adult, a common sign is nervousness shown by darting movements and tremors. The plumage remains in good condition but has a washed-out appearance due to loss of pigment. This is mostly seen in canaries and budgerigars which, when treated with thyroid, molt and rapidly grow a new, though paler plumage.
The manifestations of thyroid dysfunction described in young birds arise spontaneously, from an upset of the physiological control of metabolism. Microscopic examinations of thyroids from both adults and young at necropsy, may fail to show more than moderate evidence of over-activity or enlargement. Several species and budgerigars in particular, however, may develop excess growth of certain cells in the thyroid gland. This growth can be huge, without obviously affecting glandular function or conversely small, yet with the far-reaching results. An enlarged thyroid gland is called a "goitre" whether the output of thyroid hormone is normal, increased or decreased. Although most types of goitre found in man have occasionally been seen in birds, they are mainly rare.
Some enlargements of the gland are the result of a lack of the raw materials it needs to produce thyroxine, the active hormone. Such raw materials include iodine and the amino-acid tyrosine. Both these substances are relatively low in the diet of seed-eating birds in captivity and most reports of low thyroxine output or hypothyroidism occur in gallinaceous, psittacine and passerine birds, the groups favored by aviculturalists. Fish- and insect-eating birds on the other hand usually obtain an adequate supply of iodine and tyrosine. Hyperthyroidism (high thyroxine output) has been diagnosed occasionally. Early clinical signs of enlarged thyroids are bouts of continuous squeaking with each inspiration. On holding the bird near the ear expiration is heard as a low hiss. As the days pass, the squeak becomes incessant and quite beyond control. Breathing becomes increasingly difficult, weight is lost, the bird gasps for breath and sits huddled on its perch. Progressively less food is taken, because swallowing becomes difficult owing to constriction of the opening between the crop and proventriculus, due to pressure from the enlarged thyroids. Eating also interferes with the respiration. In this advanced stage the effort of trying to escape when approached or handled may be sufficient to cause heart failure. If the enlargement is mainly in a backward direction it presses on the veins entering the heart, or in very advanced cases on the heart itself and causes cardiac embarrassment. If the breast or back is auscultated at this stage, bubbling sounds may be heard which indicate that back pressure of blood in the great veins and lungs has caused congestion and oedema of the lungs. Such a bird is prone to chills and infections. Death, however, may occur before a swelling is detectable in the neck. In fact those birds with neck swellings usually show relatively slight clinical signs because the thyroid enlargement in such cases is less confined and protrudes into the elastic tissues of the neck.
Removal of the thyroid is rarely possible or successful and is likely to be fatal. The demarcation between normal and abnormal tissue is seldom visible, therefore it is not practical to remove only the abnormal portions. The large numbers of blood vessels and nerves, and the closeness of the esophagus and trachea also make surgery impracticable. In some cases, a reduction of the mass or an amelioration of the clinical signs have followed iodine, tyrosine or thyroid replacement therapy, in the form of diets containing these substances. In the main, however, the disease takes a relentless course leading to death. It is interesting to speculate how far breeding for size and weight or indeed any of the show characteristics of budgerigars may have contributed to the frequency of this unpleasant and common disease.
The Parathyroid Gland:
The parathyroids are tiny structures lying just behind each lobe of the thyroid gland. As stated previously they are largely concerned with the utilization of calcium and phosphorus, influencing their level in the blood by varying absorption from the gut and mobilization from the bones. Calcium and phosphates are very important in the building and maintenance of bone--and in birds, egg-shell production --as well as for the conduction of impulses through the nervous system. In diseases affecting the parathyroids any of these activities may become deranged. Direct proof is lacking, but experience with mammals and poultry provide considerable evidence that defects of parathyroid function also occur in cage birds. Although an out-right lack of oyster shell grit in breeding females will result eventually in soft, non-shelled eggs, parathyroid hormone (parathormone) enables the birds to draw stores of calcium and phosphate from the bones for a time. The production of soft shells when an abundance of soluble grit is fed, denotes a possibly defective parathyroid gland. Fragile bones in adults and a tendency towards rickets in young parrots are probably related in many cases to abnormal functioning of this gland. A proportion of the vague, undiagnosable nervous disorders in adult birds of various species such as tremors, weakness, paralysis, convulsions and sudden blindness, have their parallel in mammals and have been related to parathyroid exhaustion or disease. Little research, however, has been done on the diagnosis and treatment of parathyroid disease in birds.
The Adrenal Gland:
The two adrenal glands lie under the vertebral column just in front of the kidneys and are usually pinkish-cream in color. The adrenal gland is known as the stress gland. Whenever a bird is chilled, overheated, frightened, or if it is invaded by pathogenic organisms, this gland immediately stimulates whichever organ or mechanism is involved in the body's urgent defensive reaction. The cortical tissue also produces hormones which have a limiting effect on the body's inflammatory reactions. Any lack of this hormone will therefore allow repair processes to continue and pain to persist long after the cause of the trouble has ceased, producing such conditions as chronic arthritis and oedema. In an unsuitable climate, on a deficient diet, after prolonged disease or after over-breeding, the gland can become exhausted beyond recuperation. This state of affairs probably occurs much more often than is realized, and quite likely accounts for many deaths attributed to shock. Much research work is necessary before we can appreciate the full importance of this gland in birds. Some diseases in which a link-up with the adrenal cortex is suspected, include nephritis and gout, obesity, thyroid enlargement, French molt and other feathering disorders, as well as various diseases affecting the heart and circulation. Others include increased susceptibility to quite mild stresses such as being startled, quite brief or gentle handling, heat, cold, sudden exercise and the process of egg production and laying.
The Pancreas:(Islets of Langerhans)
In mammals diabetes, which is a disorder of the Islets of Langerhans, is a well known disease, but there is virtually no evidence that it occurs in birds.
The Thymus Gland:
There is virtually no information concerning diseases of this gland, although tumor formation has been reported in budgerigars.
Although the origins of both male and female gonads are similar, the secretions have diametrically opposite effects on secondary sex characteristics. The chemical structure of the male and female hormones, the androgens and oestrogens respectively, are similar not only to each other but also to vitamin D and a number of other body chemicals such as the cortisone's and their derivatives. The male hormones produce male characteristics and the female hormones produce female characteristics, but each sex gland or gonad also manufactures hormones which have a little of the effects of those of the opposite sex. Sometimes, however, hormonal disorders occur and give rise to varying degrees of sex reversal. As birds have complicated patterns of territorial behavior, peck orders and courtship display behavior, it is not surprising that any bird departing even slightly from the norm is persecuted and often killed or driven away. Nature seems unable to tolerate a creature that is a little different from the crowd.
An imbalance of sex hormones can be manifested in several ways. For example, the bird will not mate or be mated, it will not sit on eggs or it becomes a bad parent and refuses to feed the young. Sometimes such a bird tries to mate a member of its own sex. From time to time, a bird may even show signs of being a nymphomaniac. Some of these states are of temporary or seasonal occurrence only; others are permanent. Some of the abnormalities described above are accompanied by other physical changes, duller or brighter plumage, and development or atrophy of one or another of the combs or fleshy appendages. It is rare for a cock which has once fertilized a hen, later to lay fertile eggs or vice versa, but it is not unknown. In less advanced cases, a previously fertile hen may begin to mount females or a once virile cock will become less aggressive and begin to behave more like a hen. These developments may represent either temporary exhaustion of the gland or excessive seasonal variation in its activity.
Sometimes a pituitary lesion is responsible or possibly an adrenal degeneration or tumor. Abnormalities have on rare occasions derived from a dual or partially dual set of gonads, male and female, in the same bird, in which the pituitary or other glands allow one set to develop to maturity at puberty and the other some time in middle life. Malnutrition can halt sexual functions but it is unlikely to allow characteristics of the opposite sex to develop. Both testes and ovaries are fairly prone to tumors, particularly in budgerigars. These tumors may or may not result in alteration of hormone secretion because they are formed of different types of gonad cell, only some of which secrete sex hormone. Those birds in which the tumor produces no hormones will show loss of sexual powers and characteristics only when the tumor cells have replaced the normal ones. Ovarian and testicular tumors in birds are significant mainly for the pressure which they exert in the confined body cavity by pressing on organs such as the kidneys, adrenals, liver and various parts of the intestinal tract. In female budgerigars there is evidence that certain disturbances in oestrogen production can cause skeletal deformities. The disease is characterized by numerous bony deposits especially affecting the spine, sternum and skull, and is known as polyostotic hyperostosis. It has been produced experimentally by implanting the female hormone stilboestrol beneath the skin.
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Hamilton & District Budgerigar Society Inc.