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- Excerpt from Diseases of Caged Birds, pages 74-75
- Author: Elisha W. Burr.
TFH Publications Inc, ISBN 0-8138-0362-4
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- Goiter (thyroid dysplasia), Goiter can occur as a result
of hypothyroidism caused by iodine deficiency. Some authors consider
it very rare (Rosskopf et al. 1982). Others have reported high
incidence of this disorder (Blackmore and Cooper 1982). This can
be explained by geographical considerations and dietary habit
conditions.
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- Etiology. As in all animals, iodine is required for thyroxin
synthesis. A deficiency in the diet can result in decreased secretion
of the hormone. Other factors can also stimulate the appearance
of thyroid dysfunction (many plants (e.g., soybean) provide goitrogenic
principles that inhibit thyroxin synthesis even if iodine is adequately
supplied). This disease is unknown in seabirds, which receive
large amounts of iodine from the fish in their diet. For caged
birds eating only seeds, iodine supply can be in- sufficient and
thyroid dysfunction can appear. Oyster shell grit contains an
appreciable amount of iodine and can prevent the disease (except
in Budgerigars). As a consequence of thyroxin deficiency, the
thyroid-stimulating hormone from the anterior pituitary is released
in increased amounts and the thyroid follicles become hyperplastic.
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- Clinical Signs. Thyroid hormones stimulate metabolism.
Their deficit results in systemic disturbances. Affected birds
are lethargic and inactive and exhibit poor condition (dry skin,
ragged plumage). They are unable to maintain body temperature
when exposed to environmental changes, their blood cholesterol
increases, and body weight tends to increase due to the deposition
of excess fat. Many birds with fatty tumors and fatty liver have
hypothyroidism (Sitbon and Mialhe 1980). The affected birds also
show slower heart and respiratory rates and reduced fertility
and excrete small, constipated droppings.
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- Thyroid insufficiency presents a characteristic feature in Budgerigars,
in which dystrophy of the glands produces mechanical obstruction
of the respiratory and digestive tracts. The weight of the glands
is normally 5-40 mg, and when thyroid insufficiency is present,
may exceed 300 mg (Schone and Arnold 1980; Black- more and Cooper
1982). Both lobes of the thyroid gland lie at the thoracic inlet
where space is limited; thus an increase in size compresses the
trachea, the syrinx, and sometimes the esophagus.
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- The major clinical signs are labored respiration with squeaking
noises. These symptoms are often considered asthmatic or a respiratory
infection (chronic respiratory disease). Digestive disturbances,
such as regurgitation of food, slow emptying of the crop, and
crop dilatation, are also commonly seen. Severe loss of weight
(emaciation) ensues (Wise 1980).
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- Diagnosis. Diagnosis of thyroid disturbance can be made
by blood thyroxin evaluation. The normal values vary according
to species. Nor- mal ranges for eleven species have been suggested
by Rosskopf et al. (1982) in a study where thyroxin was measured
in more than fifty species (Table 12.1). Hyperplasia of the gland
usually cannot be palpated or seen by X-ray examination. Gastrointestinal
disturbances (e.g., slow emptying of the crop) may be revealed,
however, after giving a barium meal (Lafeber 1965).
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- Therapy and Prevention. Goiter can be treated successfully
using either iodine or levothyroxine. Iodine can be given by injection
to obtain rapid improvement or orally for mild cases or preventive
medicine. Lafeber (1965) recommended daily injections of 20% sodium
iodide, 0.01 ml in chronic and 0.02-0.03 mi. in acute conditions.
Marked improvement may be obtained within 3 days. For oral therapy,
Lafeber recommended adding one drop dilute Lugol's solution (2
parts Lugol's solution to 28 parts distilled water) to fresh drinking
water.
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- Steiner and Davis (1979) recommended a solution of 1 ml 7% Lugol's
solution in 14 ml water. Every day for 2 weeks, 1 mi. diluted
iodine solution is diluted in 1 oz drinking water. The hormone
thyroxine is available in thyroid extract or as levothyroxine.
The treatment is given orally in the drinking water, the dosage
varied according to the bird's drinking habits (Rosskopf et al.
1982).
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- To prevent recurrence of the disease, the diet may be supplemented
with iodine, finely ground oyster shell grit, or cod-liver oil.
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