The Case for Iodine Supplementation in Birds in New Zealand

New Zealand has a long history of iodine deficiency, and understanding that history helps explain why iodine nutrition deserves particular attention in some of our birds.

Iodine is required for the production of thyroid hormones, which play important roles in metabolism, growth, development and temperature regulation. When dietary iodine is inadequate, the thyroid gland can enlarge as it attempts to compensate, resulting in thyroid hyperplasia, commonly known as goitre.

For birds eating diets naturally low in iodine, particularly seed and grain-based diets, this can become a significant nutritional problem.

New Zealand Has Naturally Low Iodine Soils

New Zealand soils are naturally low in iodine. Historically, this contributed to widespread iodine deficiency in people, with goitre once particularly common in New Zealand children.

Public health measures, including the iodisation of salt and later mandatory iodine fortification of most bread, were introduced to increase iodine intake in the human population.

The same environmental issue is relevant when considering bird nutrition.

Plants cannot provide significant amounts of a mineral that is poorly available in the soil in which they are grown. As a result, locally produced grains, fruits and vegetables should not automatically be assumed to provide adequate dietary iodine.

Why Iodine Matters to Birds

Iodine is an essential component of the thyroid hormones produced by the thyroid gland.

These hormones are involved in:

• Metabolism
• Growth and development
• Thermoregulation
• Reproduction
• Feather development and moulting
• Normal function of multiple body systems

When iodine intake is inadequate, the thyroid gland attempts to compensate by increasing its activity and size.

Over time, this can result in thyroid hyperplasia and goitre.

Some Birds Are Particularly Susceptible

Goitre is particularly well recognised in budgerigars, especially those maintained on predominantly seed-based diets.

Cockatiels may also be at increased nutritional risk when fed poorly balanced seed diets. Thyroid disease associated with nutritional imbalance has also been reported across a range of other avian species.

The important point is not that every bird in New Zealand requires additional iodine.

It is that diet matters enormously.

A bird eating a properly formulated pellet diet is in a very different nutritional situation from a budgerigar eating predominantly millet, or chickens receiving large amounts of scratch grain and household foods.

What Happens When a Bird Doesn't Get Enough Iodine?

Without sufficient iodine, the thyroid cannot efficiently produce thyroid hormones.

In response, the gland may enlarge as thyroid cells proliferate in an attempt to capture more iodine and maintain hormone production.

This compensatory enlargement is what produces a goitre.

Interestingly, a bird can have substantial thyroid enlargement while circulating thyroid hormone concentrations remain relatively normal because the enlarged gland is temporarily compensating for the deficiency.

Signs of Thyroid Enlargement and Dysfunction

The clinical signs associated with goitre and thyroid dysfunction vary depending on the severity of the condition and the structures affected by the enlarged thyroid.

Possible signs can include:

• Changes or loss of vocalisation
• Respiratory noise or difficulty breathing
• Reduced exercise tolerance
• Regurgitation or difficulty swallowing
• Weight changes
• Lethargy and reduced activity
• Poor feather quality or abnormal feather development
• Delayed or abnormal moulting
• Reproductive problems
• Reduced hatchability or increased embryo mortality

In severe cases, an enlarged thyroid can place pressure on surrounding structures within the body and become life-threatening.

These signs are not specific to iodine deficiency, so iodine deficiency should not be diagnosed from symptoms alone.

The Budgerigar Connection

One of the classic studies into thyroid disease in budgerigars was published by Blackmore in 1965.

In a captive population of approximately 400 budgerigars, thyroid hyperplasia was extremely common at post-mortem examination. Around 85% showed some degree of thyroid hyperplasia, and approximately 24% of deaths were attributed directly to the condition.

The nutritional problem was associated with the low iodine content of the predominantly seed-based diet.

Although this research is now decades old, it demonstrates just how significant nutritional thyroid disease can become when susceptible birds are maintained on iodine-deficient diets.

Seed-Based Diets Are Part of the Problem

Many commonly fed seeds and grains provide inadequate levels of several important micronutrients, including iodine.

This is one reason why an all-seed diet is not considered nutritionally complete for parrots.

Birds also cannot be relied upon to balance their own micronutrient intake simply by being offered a variety of foods. Selective feeding is common, particularly in parrots, and preferred foods are not necessarily the foods that provide the nutrients they require.

This makes the overall formulation of the diet important.

What About Goitrogenic Foods?

Another consideration is the presence of naturally occurring compounds known as goitrogens.

Goitrogenic compounds can interfere with iodine utilisation or thyroid hormone production.

Foods containing goitrogenic compounds include some:

• Brassicas, including cabbage, kale and broccoli
• Soy products
• Millet
• Flaxseed
• Rapeseed
• Peanuts

This does not mean these foods are inherently bad for birds or need to be eliminated from a balanced diet.

The greater concern is when a bird is already receiving marginal iodine and a large proportion of its diet consists of foods that may further interfere with normal iodine utilisation.

Again, the overall diet matters more than any individual ingredient.

Does Every Bird in New Zealand Need Iodine Supplements?

No.

This is an important distinction.

A bird eating an appropriately formulated commercial diet should generally receive iodine as part of that formulation. Adding additional iodine without considering what is already present can result in excessive intake.

Supplementation becomes more relevant when assessing birds consuming diets such as:

• Predominantly seed-based diets
• Scratch grain diets
• Poorly balanced homemade diets
• Whole-food diets without appropriate formulation
• Diets containing little reliable dietary iodine

The species, life stage, reproductive status and overall diet should all be considered before deciding whether supplementation is appropriate.

Diagnosing Iodine Deficiency and Goitre

Diagnosing thyroid disease in birds can be challenging.

The thyroid glands are located within the thoracic inlet and may not be palpable during a routine physical examination, even when significantly enlarged.

Diagnosis may involve a combination of:

• Dietary history
• Clinical signs
• Physical examination
• Radiographs or other imaging
• Thyroid hormone testing
• Response to appropriate treatment

Radiographs may sometimes demonstrate displacement or compression of nearby structures caused by an enlarged thyroid.

Thyroid hormone testing can also be difficult to interpret in birds. A compensating enlarged thyroid may continue producing hormone concentrations within the normal range despite underlying iodine deficiency.

Supplementing Iodine

When iodine deficiency or goitre is suspected, supplementation should be approached carefully.

Treatment may involve iodine supplementation at therapeutic levels for a period of time, depending on the individual bird and severity of the condition.

Lugol's iodine has historically been used in avian medicine, but concentrated iodine preparations can be dangerous if incorrectly dosed and should be used under veterinary direction.

For prevention, the simplest approach for many companion birds is an appropriately formulated diet that already contains adequate iodine and other essential micronutrients.

Birds maintained on seed, grain or homemade diets require considerably more thought to ensure their micronutrient requirements are actually being met.

The Takeaway

New Zealand's naturally low iodine environment makes iodine an important micronutrient to consider when evaluating bird diets.

That does not mean every bird needs an iodine supplement.

The strongest case for supplementation exists when a bird's species, diet and nutritional history suggest that iodine intake may be inadequate, particularly in birds maintained predominantly on seed or grain-based diets.

Rather than supplementing blindly, look at the entire diet.

A well-formulated diet should provide iodine alongside all the other vitamins, minerals, amino acids and nutrients a bird requires. When the diet cannot reliably provide that, targeted supplementation may have an important role.

For birds showing possible signs of thyroid disease, dietary assessment and veterinary investigation are appropriate before simply adding iodine to the diet.

By Sam Hurley and Jemma McLean

References

Blackmore, D.K. (1965). The pathology and incidence of thyroid dysplasia in budgerigars (Melopsittacus undulatus). Veterinary Record, 75, 1068 to 1072.

Koutsos, E.A., Matson, K.D. & Klasing, K.C. (2001). Nutrition of birds in the order Psittaciformes: A review. Journal of Avian Medicine and Surgery, 15, 257 to 275.

Loukopoulos, P., Bautista, A.C., Puschner, B., et al. (2015). An outbreak of thyroid hyperplasia (goitre) with high mortality in budgerigars (Melopsittacus undulatus). Journal of Veterinary Diagnostic Investigation, 27(1), 18 to 24.

Mann, J. & Aitken, E. (2003). The re-emergence of iodine deficiency in New Zealand? New Zealand Medical Journal.