Susan E. Orosz, PhD, DVM, Dipl ABVP (Avian), ECAMS
Veterinarians are commonly asked questions relating to avian nutrition and make clinical judgments regarding nutrition in avian patients with various disease states. However, nutrition is often only touched upon in the veterinary curriculum and rarely are avian species discussed. The following information focuses on the information that veterinarians need to know to improve their quality of care to their avian patients, particularly psittacine species.
What Are the Nutritional Feeding Strategies of Psittacine Birds?
The types of foodstuffs consumed in the wild are used as a tool to classify groups of animals for helping to determine the nutritional requirements. Generally the birds within the Order Psittaciformes [parrots] are considered to consume plant-based foodstuffs and are classified as florivores, or animals that eat seeds, fruits, nuts, bark, roots and berries. Within this category, further sub-classifications can be made including granivory (eats primarily seeds and grains, like budgies and cockatiels), frugivory (eats primarily fruit, like many of the macaws, e.g. green-winged macaw), and nectarivory (nectar eaters like lorikeets and lories). Yet many parrots cross over these artificial lines and consume a much larger variety of foodstuffs. An example is the scarlet macaw (Ara macao), which is classified as a frugivorous-granivorous (grain and fruit-eating psittacine). In addition to the basic classification based on general foods eaten, ingredients consumed vary over time depending on nutrient availability, sex of the bird, and by age.1 However, there are some species that have a very limited diet, like the glossy-backed cockatoo (Calyptorhynchus lathami), which feeds almost exclusively on seeds from a single species of tree in the bird’s native environment.
Table 1. Feeding strategies and common diet ingredient of wild psittacine birds. (Table adapted from Koutsos, et al.1)
Species Name Feeding Strategy Common diet ingredients Time spent feeding*
Blue and gold macaw
Florivore Seeds, fruits, nuts NR
Florivore Seeds, nuts, berries,
Frugivore Fruits, palm nuts, seeds NR
Frugivore fruit (85% from palm fruit) NR
Frugivore-granivore Fruits, nuts, bark,
Granivore Seeds NR
Granivore Seeds (prefers soft,
young overmature, hard seeds)
Granivore Palm nuts
(50% lipid content)
Omnivore Seeds(primarily sunflower),
*NR indicates not reported.
Nutrients are defined as the components in the diet that provide the energy to maintain life and provide the precursors for the synthesis of the structural and functional macromolecules, such as lipids (i.e., fats), proteins, carbohydrates and water. Micronutrients are the smaller components that comprise the diet and include vitamins and minerals. Essential nutrients are required for optimal health. They may be needed for metabolism and may not be produced by the body in sufficient amounts to meet metabolic demands. The components of the nutrient requirements are well known in some of the domestic galliforms like chickens and turkeys. Essential nutrients are required in similar proportions with these species and for this reason have been used as a model for parrots.
The physiology of a particular parrot species determines its nutrient requirements. Requirements are determined for three physiologic states: basal, maintenance and total. The basal requirements are those needed to maintain basic life functions, that is, those needed to replace losses inherent in being alive. The maintenance requirement is the amount of nutrients needed for basal functions including the activity of finding and consuming food, interacting with other animals, and maintaining body temperature. The total energy requirement is the combination of all requirements for life and its stages including growth, reproduction, and molt.
It is very important to understand the principles behind how nutrient requirements are determined, particularly with companion species of birds. As previously mentioned, few nutrient requirements have been looked at scientifically, so they are often based on the best guess from those derived from galliforms.
The problem with companion birds is that their requirements are often not well established. The Association of Avian Veterinarians [AAV] worked with a panel of experts in diverse areas of avian nutrition to provide general recommendations for psittacines and passerines (so-called soft billed or perching birds like canaries and finches). These values were the best collective guess to start the discussion on nutrient requirements in these groups of birds.3 As avian veterinarians, we realize that individual pet bird species have differing needs based on our clinical impression over time, and the natural behaviors of their wild cousins. Additional concerns exist about feeding whole-food diets in mammals, and providing foods that allow our companion birds to exhibit their natural foraging behaviors. These concerns are adding to a better understanding of the parrot’s nutritional needs.
Birds in the wild do not necessarily select adequate diets nutritionally, although they appear to be able to balance their energy needs, amino acids and calcium, but not their needs for other requirements.1 Birds in captivity do not appear to select appropriately, either. For example, a self-selected diet in African grey parrots (Psittacus erithacus)4 resulted in a diet that was deficient in a total of 12 dietary components consisting of vitamins, minerals and amino acids. A recent dietary approach was to provide a formulated diet (pelleted or extruded mixture) that provides all of the required nutrients above the estimated requirements. This approach has greatly improved the health of companion birds over an all-seed diet, but there are some shortfalls. There is concern about the lack of variety for species that often have a huge selection of food items in the wild; and these diets offer no opportunity for birds to display their innate foraging behavior.
As we learn more about ways to provide foraging opportunities, things will change in how companion birds are fed. Presently, the addition of vegetables and fruits to the diet for variety and for enrichment suggests that nutrient dilution may occur. Theoretically, that would require that the diet be reformulated to increase the non-energy portion of the diet to reduce this problem. However, this problem becomes more of an issue when the bird is eating a smaller portion of the formulated diet than the table foods offered. The reason that this may not be observed commonly is that most of the domestic fruits and vegetables are predominately water.
Protein & Amino Acids
Protein levels consumed must meet the nitrogen requirements for that species in its housing condition and life stage. Growing chicks require greater amounts of protein especially hatchlings. Hens laying large clutches of eggs also require larger amounts of protein than those at maintenance. Birds within a dietary strategy (e.g., granivorous) that have an increased body size also have higher protein requirements than smaller bird species.
Feathers compose the largest portion of the protein requirements of birds. In budgies, feathers equal 28% of the total body protein. Molt results in increased protein needs, and these needs differ from those required for the general body. Feathers are enriched with amino acids. Molt is also expensive energetically as the bird loses insulation during that period, consequently requiring increased energy to maintain his body temperature.
High-protein diets have been assumed to lead to gout in birds, but this supposition has not been supported by research. Adult male cockatiels, when fed diets with up to 70% crude protein for 11 months, maintained their body weight and general body condition without evidence of kidney damage. It would appear that sudden changes to high-protein diets might lead to possible nephritis (inflammation of the nephron, the functional unit of the kidney) or gout.1 However, there is no research at present that indicates that this hypothesis is valid. But sudden changes are not recommended.
Vitamins A, D, E, and K are fat-soluble vitamins, and their excretion is more problematic than the water-soluble ones. Vitamin A is the vitamin that is more likely to be deficient in both captive and wild birds, as the amount contained in foodstuffs can be quite variable. Inadequate levels of vitamin A can, for example, cause the fundamental cells of the respiratory and GI tracts to change morphology so they can no longer function properly.9 Birds deficient in vitamin A exhibit signs of anorexia (lack of appetite), poor conditioning and increased susceptibility to infection.10
Vitamin-D activity is found in a group of related vitamins including vitamin D3, vitamin D2 and other metabolites. Birds are able to synthesize vitamin D but require an adequate amount of sunlight to do so. Because most companion birds do not have sufficient ultraviolet exposure for vitamin-D production, they need a dietary source of vitamin D. Vitamin D has hormonal actions, as it regulates calcium and phosphorus metabolism including bone mineralization and eggshell formation. Vitamin D-deficient hens lay eggs with thin shells and develop softening bones and resulting fractures. Overdoses in vitamin D are associated with increased mobilization of calcium with soft tissue mineralization. Recent unpublished data suggest that increased levels of vitamin D can also result in kidney failure (D. Phalen, unpublished data, October 2003).
Vitamin E consists of 2 groups of compounds with antioxidant activity and they act with enzymes to stabilize and protect the cell membranes. These enzymes require some of the trace minerals including zinc, manganese, selenium, and iron for proper function. When deficient, the absolute requirement of vitamin E increases, demonstrating that many of the nutrients are linked. Deficiencies of vitamin E result in a number of symptoms that relate to cell membrane dysfunctions, including neurological signs.
The mineral required in the largest quantity is calcium. It is necessary for bone mineralization and eggshell calcification, as well as proper nerve conduction. The calcium requirement(s) for psittacine species have not been determined, but the maintenance requirement for chickens is 0.1% of the diet. Many of the seeds consumed by companion birds are less than 0.03% of the diet, suggesting that the requirement is larger than 0.05%. African grey parrots are particularly prone to hypocalcemic (low calcium) seizures. This problem seems less apparent clinically when birds eat at least half of their diet as pellets because vitamin D3 is provided. African greys may have a higher requirement for exposure to unfiltered sunlight. Sunlight is needed to convert the inactive form of vitamin D to the active form or the active needs to be supplied in some food on a regular basis.
The requirement for growing parrot chicks in unknown, but they would be expected to require a similar ratio of calcium to phosphorous ratio (between 1.4:1 and 4:1), assuming the vitamin-D levels are adequate. Calcium deficiency occurs when there is too little calcium or the active form of vitamin D, or too much phosphorus in the diet. The lack of calcium and the active form of vitamin D in all-seed diets is the underlying problem with egg binding in female cockatiels.
Formulated diets for parrots consist of pellets, extruded pellet-appearing foods, and whole grains and/or seeds with pelleted material added to balance the entire product (e.g., Nutri-Berries™ and AviCakes™). There are some seed-based foods where a pellet is added to balance the seed mixture, or a vitamin/mineral mix that is coated on the outside of the seed. All of these products may be considered “balanced” from a nutritional point of view.
True pellets are made by grinding a variety of grains based on the manufacturer’s recommendations. Vitamins and minerals are added to the mixture to make the final product nutritionally balanced. Grinding reduces particle size to make it easier to produce a homogenous mixture. This process is used so that the bird is unable to pick out and eat only the components of the food that he likes. By grinding and mixing the food, it ensures that the bird receives this balanced diet.
Nutri-Berries™ and Avi-Cakes™ utilize whole grains and seeds that are mixed with a pellet that balances the product before it is stuck together. These products are similar to pellets except that the ingredients are not ground up, run through high heat and then pressured into the pellet shape.
Other seed products (a.k.a., “seed mixes”) put pellets into the mixture to balance the entire product. This would require that the bird eat those pellets along with the seed to receive a balanced meal; unfortunately, few parrots do. Some of these products have the seed coated with vitamins and minerals to balance the entire product. The coatings are often colored and are applied to the seed hull; however, the vitamin and mineral intake from the coatings is markedly reduced once the bird de-hulls the seeds.
This information will hopefully help avian veterinarians, technicians and bird owners to better understand the important components of avian nutrition. The values that are used as requirements are just a starting point for determining the needs of a diverse group of birds classified as psittacines. Many aviculturists have learned through trial and error that some species are not successful in captivity without certain food items. These nuances need to be added to the body of knowledge to provide improved health and well being for these magnificent creatures.
Acknowledgments: The author thanks the Lafeber Company for its support of this manuscript.
Disclaimer: Dr. Orosz is the veterinary consultant for the Lafeber Company. new
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