by D.M. Jones, U.K.
Director of Zoos, London and Whipsnade
From the point of view of their digestive system, parrots are a relatively homogeneous group of birds equipped to derive their nutrients principally from seeds and fruits. Adaptations of the bill in some species have evolved for probing, cutting and crushing, and the lories and lorikeets have "brush" tongues with which to extract nectar and pollen. It has been shown recently that many of these parrots inadvertently or purposely take in a considerable quantity of insect material, and it is likely, contrary to some popular opinion, that almost all species normally ingest some animal protein in the wild. This has an important bearing on feeding in captivity.
About half of the clinical cases involving parrots referred by veterinary practices to the Zoological Society's Veterinary Department are suffering from a deficiency of one or more nutrients. Traditionally, and presumably based on limited observations in the wild, parrots are often fed diets consisting almost exclusively of seeds. It is probable that many parrot keepers maintain their birds, apparently successfully, for many years on this type of diet. Although minor deficiencies might be shown if extensive laboratory analysis of tissues were possible, the bird eating such a diet would survive many years providing no other physiological insult in the form of changes in the environment, diet or the presence of a significant pathogenic organism was to upset this tenuous balance. It is unlikely that such a bird would be productive in terms of reproduction and the successful rearing of young birds.
In the wild, even small quantities of protein from an animal source would provide birds with essential amino acids which are not readily found in seeds or other plant material. In addition the selective activities of the bird in searching for food would enable it to take plant material with a higher protein content than that found in stored seeds. In addition to this, the vitamin content of all stored products deteriorates very rapidly and even if parrots are able to manufacture certain of the vitamins (and this is not known), the bird kept on a standard pet shop parrot mix could quickly become deficient, particularly in vitamin A.
The third potential nutritional problem resulting from this type of diet is a lack of calcium or phosphorus, or, more likely, an imbalance of the two. This is often exacerbated by relatively low circulating levels of vitamin D3, which the bird should be given in its diet. Theoretically, many birds are probably able to make their own D3 with the help of direct sunlight, but this is something which many pet parrots rarely see. Seeds are very variable in their calcium and phosphorus content, and by feeding predominantly one form of seed or another it is easy to create an imbalance of these two major minerals. Although abnormalities of the skeleton as a result of nutritional deficiencies are not common in parrots, they may be predisposed to in the egg-laying female. After a while the body's reserves of calcium become depleted resulting in thin-shelled eggs, longbone fractures and possibly disease of the nervous system.
It is not enough simply to have diets which are high in protein. Certain foods, notably of plant origin, do not contain some of the amino acids necessary for the structural components of living cells or for the complex enzymes needed for metabolism. Until we have a clearer idea of where exactly such birds obtain essential amino acids in the wild, it is a good policy to give captive parrots a small quantity of protein from an animal source as part of its daily diet. This might be given in the form of dairy products such as milk-based baby foods, Complan (Glaxo Limited), Farex (Glaxo Limited) or cheese, or a meat-based food such as lightly cooked beef, canned pet food or the expanded dried pellets containing meat meal which are now used extensively for laboratory and domestic carnivore diets. Certain poultry rations are also rich in protein of a high biological value, but care must be taken in the feeding of these diets and more will be said on this subject later. In the young bird, deficiency of any amino acids will lead to a reduced growth rate, inadequate muscular development and bone deformities. The development of feathers will also be impaired. The adult bird has a much lower requirement for amino acids, but any process involving structural regeneration is likely to be affected. Thus the principal sign of protein shortage in the adult is an inability of the bird to form new feathers after moulting. This probably the commonest cause of poor feather growth seen in parrots at the hospital at Regent's Park.
In order to lay a clutch of normal eggs, the female will have a seasonally higher requirement for protein, and as egg albumin is itself one of the best sources of all the essential amino acids, the bird will need these amino acids in the diet to produce the albumin. Protein cannot be used by the body for these many processes without an adequate energy intake as well. Simply increasing the protein levels is often not sufficient without ensuring that the animal's intake of energy rich foods, which in the case of psittacines will be complex carbohydrates, is also adequate. In practice the high content of seeds in the diet solves this problem.
The parrot derives the majority of its energy requirements from the carbohydrate in seeds, but as some of these seeds also contain oils, a part of the energy intake will be obtained from this source. An energy shortage is most unlikely to occur in the captive parrot unless the owner fails to provide sufficient seed. Most owners, particularly of the single pet bird, have a tendency to over feed with the result that birds store excess subcutaneous and intra-abdominal fat. This may ultimately lead to deposition of fat in the liver resulting in liver failure. Arteriosclerosis is also very common in psittacines, particularly ageing birds, but whether arterial disease can be directly linked to a high energy content of the diet has not been proven. Diets high in fat, in our experience, also led to fatty infiltration of the cardiac muscle with resultant heart failure and, while these problems are most commonly seen in show budgerigars, they do occur in other members of the psittacine family.
Stored foods are likely to have a low vitamin content. Although some fresh green foods may contain adequate levels of vitamins A and C, it is always wise to supplement the diet with a comprehensive vitamin supplement, either by using one of the prepared pelleted foods mentioned at the end of the paper or by using one of the well known paediatric drops obtainable for your local veterinary practice or chemist. Although we have at Regent's Park seen cases where a picture of general debility accompanied by nervous signs appears to respond to supplementation with B complex vitamins, by far the most important cause of problems in this category is a shortage of vitamin A. The most common lesion caused by this deficiency in parrots is a hyperkeratosis of the oral mucous membrane which is often accompanied by oral candidiasis and secondary bacterial infections, sometimes extending down into the oesophagus. These birds are usually in poor condition. In view of the fact that there has been a suggestion recently that an excess of vitamin A in the diet might predispose to the condition known as "French moult", the owner should be aware that over-supplementation with vitamins will also tend to produce problems. Our current recommendations for supplementation of vitamin A in parrots, based on experience and the known requirements for maintenance for poultry, are 200 international units per day for parrakeets, 400 units a day for African and Amazon parrots, and 600-700 units for the larger macaws.
Owing to the lack of research work carried out on parrots almost nothing is known about their susceptibility to other diseases which might be related to nutritional deficiencies. Iodine deficiency has been well documented in the budgerigar and thyroid lesions associated with lack of dietary iodine have been seen in other species of small parrakeets.
From the relatively small amount of scientific information that has been collected it is evident that many parrot owners are not giving their birds sufficient amino acids or fat soluble vitamins. There is also a general feeling, supported to some extent by observations in this laboratory, that the nutrient quality of many seeds now being used is not as high as it used to be. Furthermore, many batches of seeds are contaminated with moulds which are often not apparent to the naked eye but which become evident on microscopic examination. We do not yet know whether these moulds are toxin producers, but a mild degree of liver damage is frequently seen on histopathological examination of the livers of psittacines submitted for examination at Regent's Park and there is a possibility that these lesions may be caused by low grade toxic substances. In itself the degree of damage may not be immediately significant, but it may predispose the bird to other problems, notably an infectious disease which it would otherwise be able to resist. With the increasing human demand for high grade cereals, it is more and more likely that if parrot keepers have to depend on imported seeds for feeding birds the quality of these seeds will not be high. Seed importers selling directly to the trade carry out very little quality control and almost never examine the nutrient content of their products. This means that the possibilities of buying seed only from a known source under known growing conditions should be considered and that any dealer involved should be obliged to carry out quality control checks at regular intervals to cover the seeds' nutrient content, fungal contamination, and pesticide and heavy metal residues. This will undoubtedly increase the cost of such seed but, in view of the increasing value of many of the birds to which it is fed, this would be acceptable to most owners.
Although seeds will undoubtedly still form a major part of the diet of psittacines, the use of commercially manufactured foods should be considered because of their known nutrient content, the fact that they contain reasonable levels of animal protein, and that they are fortified with stabilised vitamins. The major human and animal food manufacturers are obliged by law to carry out the type of quality control needed, and initial trials with parrots using some of these diets suggests that many of them are quite acceptable given a period of adjustment. Keepers of the more specialised psittacines, although they may not be aware of the nutrient content of the products, are already using such materials, notably in the form of baby food and milk powder based products suitable for infants and convalescent human adults. Such products include for example Ovaltine (Ovaltine Limited), Complan, Farex and the Heinz range of baby foods.
Probably as a result of this, it is rare that nutrient deficiencies occur in these more "specialised" species. The majority of parrot owners are interested in the less specialised species and in the absence of more specific quantitative information it would be worth trying some of the pelleted foods available for domestic stock. Now that many different flavours, textures and pellet sizes are available for dogs and cats, it is worth trying some of these to establish which are the most palatable. Most of these diets have a protein content ranging from 20-35%, the higher levels usually being fed to cats and growing puppies. At the present time we have to assume that most parrots will require a diet containing about 18-20% protein for maintenance, rising to 25-30% for egg production and rearing of the young. If one third of the seed in the diets now being fed to parrots was replaced by an expanded pellet containing 25% protein this would probably ensure an adequate supply of essential amino acids for maintenance. Birds which were laying eggs or rearing young could either be given a higher proportion of the expanded pellet in the diet (up to one half of the dry food content) or a pellet with a higher protein level could be used. Fine "crumbs" made for rearing chickens might be used as an alternative in diets to provide the extra nutrients for successful reproduction, but this high plane of nutrition must be reduced as soon as young birds leave the nest because damage to the liver and kidneys may result from their prolonged use.
When using these products, the vitamin A content of the diet should also be checked to establish whether an additional quantity should be given. Your local veterinary practice can help you with these calculations.
Much of what has been said in the paper suggests that we have very little hard data on the nutrient needs of psittacines. Feeding these birds on diets whose component analysis is known would go a long way towards obtaining more quantitative information.
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