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Issues in Avian Nutrition: Part I
By Tom Roudybush
For Exotic Bird Report Volume 5 Number 1 (3/1/1993)


There are areas of avian nutrition which are on the cutting edge. The data we have available point us in a direction without giving us the outcome of traveling that way. Below I present my conclusions based on the directions to which the data are pointing from my perspective. Please be aware that the direction that we as nutritionists move may change when more data become available. This is my view of where we are now and where the data seem to lead us and not a detailed outline of the future.




Birds regulate food intake with respect to energy density. That is, birds eat primarily to regulate the amount of energy they ingest. Intake of any nutrient is, therefore, regulated by the energy density of the diet and the concentration of the nutrient in the diet. A diet which is high in energy, ie. high in fat, must also be high in all other essential nutrients to be adequate. For example, a diet containing 20% protein and 3.75% fat was found to be adequate for growth in cockatiels (1). To maintain the ratio of protein to calories in the diet, more protein needs to be added to the diet as fat is increased and carbohydrate is decreased. Fat yields about 9 calories per grain when metabolized while carbohydrate yields only 4. When the amount of carbohydrate nears zero and the amount of fat reaches 60%, protein needs to be increased to 30% of the diet to maintain adequacy. This is a factor of 1.5 and is the same number by which all other essential nutrients need to be multiplied to maintain their original calorie:nutrient ratios.




Obesity is caused when energy intake exceeds energy utilization over a long period of time. The key to overcoming obesity is to increase energy utilization, decrease energy intake or both. The most effective way to overcome obesity is to do both. Moderate exercise which reduces appetite, both increases energy expenditure and decreases energy intake. It is one of the most effective changes which can be made in a weight reduction program. How increased exercise may be achieved varies with the situation, but a separation of the sources of food and water that forces the bird to move between them may be effective. Diversions which engage the bird in activity may also be effective. Other important steps in weight loss all regulate energy intake. There are a variety of steps which can be useful under various conditions. These include:


1. Regulation of food intake by offering a measured amount of food. When more than one bird is present, dominance of one bird may deny other birds access to the food. This can sometimes be overcome by offering food in more than one place.


2. Changes in food composition to reduce caloric density. Birds can consume and digest only a limited amount of food. If the caloric density is reduced to a low enough level, only a limited amount of energy can be consumed in a period of time. This limits the energy intake of the bird. This can be achieved by removing high energy food items from the diet and increasing rich sources of required nutrients.


3. Decrease fat in the diet. This has the dual purpose of limiting total energy in the diet and reducing the fat. Dietary fat is directly available for storage in fat tissues. When fat is eaten, it can be absorbed and deposited directly into fat storage cells. If the same amount of energy is ingested as carbohydrate or protein, it must first be converted to fat for storage. Since there are metabolic inefficiencies in the conversion of carbohydrate and protein to fat, equal amounts of energy ingested as carbohydrate or protein result in less fat storage than if the same amount of energy is ingested as fat.


In any weight loss program the bird must be closely monitored to assess the rate of weight loss and to determine whether any newly substituted diet is being consumed. This is best done by weighing the bird at regular intervals. Weight loss should not be more than three per cent of the bird’s body weight per week. Examination of the bird’s droppings is an easy way to determine whether the bird is eating. The dropping color may change, but the volume should be larger than the volume of the urine and bile combined from a fasting bird. In flocks it is difficult to assess the condition of individual birds. Unless birds are caught and weighed at regular intervals, some weaker or less adaptable birds may starve either from competition for food or from failure to consume newly introduced diets. Careful observation of the flock and removal and individual care of the poorer birds may be essential to prevent mortality.




Controversy surrounds the requirement for calcium in the diets of birds under maintenance conditions. Levels as high as 1.0% of the diet have been recommended, but no published experiments support this recommendation. In the Nutrient Requirements of Poultry even growing birds are fed as little as 0.55% calcium and non-laying birds are fed as little as 0.5% calcium (18). Non-laying hens maintained calcium balance on as little as 0.02% calcium (3). Male chickens maintained balance on even less though the authors concluded that 0.02% calcium was adequate for maintenance (4). Until more data are available a maintenance level of 0.1% calcium appears to be adequate.


For egg laying the level of calcium required in the diet has been stated over a wide range. There, however, is no evidence for a requirement of more than 1.0% calcium in most cage and aviary birds. Cockatiels fed 0.35% calcium were found to maintain shell thickness and conductance and egg production compared to birds fed higher or lower levels of calcium (5). In birds laying large numbers of eggs a level of 0.35% calcium is recommended to maintain bone integrity if laying cannot be stopped.


For growth 0.9% calcium appears to be adequate if balanced with 0.6% available phosphorus. There are no experiments on this though many birds have been raised on 1.0% calcium without morbidity.


Calcium is toxic during growth at levels only slightly above the requirement in birds which have been tested. Levels of 1.2% (6), 1.35% (7), and 2.5% (6) have been shown to result in poorer performance than lower levels in growing chickens. Calcium at 2.5% (6) resulted in high morbidity and mortality in pullets between 8 and 20 weeks of age. From these data it appears that the calcium intake of growing cage and aviary birds should be limited to no more than 1.2% of the diet unless specifically indicated by unique conditions.



Iron storage disease is a frequently observed but poorly understood syndrome. One effective treatment, bleeding, is usually used in conjunction with low iron diets. The cause of excess iron storage and a less invasive treatment have not been elucidated.


Iron excess in the liver is called hemosiderosis if there is no alteration of tissue morphology and function and hemochromatosis if the iron accumulation alters either the appearance or function of the cells or tissues involved (12). Iron excess, usually as hemochromatosis, has been observed in a number of species (13, 14, 15, 16, 17) and remains a problem in many pet and zoo birds. Diets with less than 100 ppm iron are recommended, because most affected birds had been consuming diets in excess of 100 ppm iron. Since practical diets with less than 100 ppm iron are difficult to formulate, this observation may prove to relate to what diets are available rather than what is needed to prevent excess iron storage. Even 100 ppm iron is in excess of the 60 to 80 ppm (18) required for growth in poultry. Corn, a major constituent of poultry diets, contains 300 ppm iron. If this level of iron were the major cause of excess iron storage, major die offs of birds fed corn based diets should have been seen. This has not happened in flocks fed diets containing 250 to 300 ppm iron for ten years. Other primary causes of excess iron storage need to be considered. Some possibilities are stresses related to disease exposure (immunologic stress 19, 20, 21); crowding; and nutritional stress related to periodic starvation associated with diet changes (22), since the disease occurs with a high frequency in recently imported birds (23). Periodic starvation has been associated with excess iron storage in the livers of reindeer (22). Immunologic stress may prove to be a factor in iron metabolism since the sequestering of many trace elements occurs after infection with coccidia in poultry (19, 20, 21). Another stress which has been shown to be associated with increased iron stores is intoxication with heavy metals (24).


With our present level of understanding of iron storage disease it appears that nutrition is, at best, a minor player in the disease. Stress factors as mediators of iron metabolism need further investigation.




1.   Roudybush, T.E., and Grau, CR.: Food and water interrelations and the protein requirement for growth of an altricial bird, the cockatiel (Nyniphicus hollandicus). J Nutr., 116:552. 1986.

2.   Shane. SM.. Young. R.J. and Krook, L.:Renal and parathyroid changes produced by high calcium intake in growing pullets. Avian Diseases, 13:558, 1969.

3.   Rowland, L.O., Jr., Sloan, DR.. Fry, J.L., and Harms, R.F1.:Calcium requirement for bone maintenance of aged non-laying hens. Poul. Sci. 52, 1415, 1973.

4.   Norris, L.C., Kratzcr, F.H., and Lin, A.B.: Effect of quantity of dietary calcium of maintenance of bone integrity in mature white Leghorn chickens. J. Nutr. 102, 1085. 1972.

5.   Roudybush, T.E.. Grau, CR. and Limberg, L.A.: Unpublished observations.

6.   Scott, ML., Nesheim. MC.. and Young, R.J.,: Nutrition of the Chicken. ML. Scott and Associates. Ithaca, NY, 1969 p 276.

7.   Smith, H. and Taylor. J.H.: Effect of feeding two levels of calcium on the growth of broiler chickens. Nature, 190, 1200, 1961.

8.   Urban. L.:Chicken feeding trials with diets containing sufficient phosphorus and increasing calcium carbonate. Nutr. Abstr.. 30:691, 1960.

9.   Smith, H. and Taylor, J.H. Effect of feeding two levels of dietary calcium on the growth of broiler chickens. Nature, 190:1200. 1961.

10. Fangauf, R.,Vogt. H., and Penner. W.:Studies of calcium tolerance in chickens. Arch. Geflugelk..25:82, 1961.

11. National Research Counsel: Mineral Tolerance of Domestic Animals. National Academy of Sciences, Washington. D.C. 1980.

12.      Lowenstine, L.J.: Nutritional Disorders of Birds. In Fowler, ME.: Zoo and Wild Animal Medicine. Pg. 204, W.B. Saunders Company. Philadelphia. 1986.

13. Griner, L.A.: Pathology of Zoo Animals. San Diego: Zoological Society of San Diego, 1983.

14.      Lowenstinc. L.F. and Petrak, ML.: Iron pigment in the livers of birds. In Montali. R.J. and Migaki, 0. (eds.) The Comparative Pathology of Zoo Animals. Smithsonian Institution Press, 1980: pp 127-135.

15. Taylor, J.J.: Iron accumulation in avian species in captivity. Dodo, J. Jersey Wildl. Preserv. Tnist. 21: 126-131, 1984.

16  Kincaid, AL. and Stoskopf, M.K.: Passerine dietary overload syndrome. Zoo Biology. 6: 79-88,1987.

17. Taylor, J.J.: Iron accumulation in avian species in captivity. Dodo, J. Jersey Wildl. Preserv. Trust. 21: 126-131, 1984.

18. National Research Council: Nutrient Requirements of Poultry. National Academy of Sciences, Washington, D.C. 1984.

19. Bafundo, K.W., Baker, D.H. and Fitzgerald, P.R.: The iron-zinc interrelationship in the chick as influenced by Eimeria acervulina infection. Poultry Sci. 63: 59, 1984.

20. Bafundo, K.W., Baker, D.H. and Fitzgerald, P.R.: Elmeria acervulina infection and the zinc-cadmium interrelationship in the chick. Poultry Sci.63: 1828-1832, 1984.

21. Bafundo, K.W., Baker, D.H., and Fitzgerald, P.R.: Zinc utilization in the chick as influenced by dietary concentrations of cadmium and phytate and by Elmeria acervulina infection. Poultry Sci. 63: 2430-2437, 1984.

22. Borch-Johnsen, B. and Nilssen, K.J. : Seasonal iron overload in Svalbard reindeer liver. J. Nutr. 117: 2072-2078, 1987.

23. Clubb, Susan, DVM. personal communication.

24. McDonald, S.E. and Lowenstine, L.J.: Lead toxicosis in psittacine birds. In Proceedings of the 25th International Symposium on Diseases of Zoo Animals (Vienna) Berlin: Akademie-Verlag. 1983: pp. 183-196.