Birds, soy and thyroid disorders
Excerpt from Diseases of Caged Birds, pages 74-75
Author: Elisha W. Burr.
TFH Publications Inc, ISBN 0-8138-0362-4
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.
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.
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.
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.
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).
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).
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.
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).
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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