Practical avian nutrition (Proceedings)

Nutrition is the process by which birds and all other animals consume food items and utilize it in the body for growth, tissue replacement or repair and the continuance of life. Good nutrition is crucial in optimizing health and preventing disease. With companion birds, nutrition must have great prominence in an overall program of wellness and health.

To examine avian nutrition the topic can be approached from the standpoint of defining nutrients and listing their importance to the different aspects of the bird's cellular and metabolic functions. Many of these avian nutrition points are provided in this lecture presentation. An additional and perhaps more interesting way of learning about avian nutrition is to examine the practical aspects of feeding birds. By evaluating and considering the different types of diets fed, recommended and available, certain principles will become apparent, helping the avian client to provide the very best diet available.

There are several main types of diets which are typically fed to pet birds. Each diet has similarities, but it is often the differences which yield the greatest amount of information. The clinician should keep in mind that different diets may work well some situations, but not all. One must consider how a diet can fit into the client's lifestyle as well. There are five major diet types available to pet birds: seeds, supplemented seed diets, seeds with fruits and vegetables, table foods, and manufactured (extruded/pelleted) diets.

Seeds are often considered by some to be the natural diet for pet birds. Certainly, many birds eat seeds in the wild, but the seeds found in the pet store, unfortunately, are not the common seeds eaten in the wild. It is nearly impossible to provide pet birds with the food for which they forage in the wild. Birds in the wild are quite different from domestically raised birds. Pet birds do not have to search for their food, nor do they have the same need for high fat, high energy foods as wild bird. Pet birds simply do not have same pressures in the home environment as they would encounter in the wild.

Seed diets are sold as a common and inexpensive food to pet birds. Pet birds readily consume seeds and there is often no difficulty in converting a bird onto this type of diet. Simple seed diets may contain a few or several different seeds (they often have a proso millet base). If no supplementation is added to the diet, then a seed only diet is not adequate for pet birds. Seeds lack several key nutrients including vitamin A, vitamin D, vitamin B12 , calcium, several trace minerals, and essential amino acids (lysine and methionine in particular, two crucial protein building blocks). Several disease syndromes are directly related to these deficiencies and can be characterized simply by the physical appearance upon examination of the bird.

An example of a deficiency syndrome arising from a seed only diet can be seen with vitamin A. As the skin and tissues around the mouth, nares, eyes and gastrointestinal tract develop, essential vitamins are needed for normal growth. A seed only diet cannot provide that essential vitamin A or vitamin D either, because it simply is not present to be utilized. Consequently, abnormal tissues develop (such as blunted choanal papillae) which can lead to poor health and disease. Clinical signs of vitamin A deficiency in birds include hyperkeratosis of the nasal passages, oral mucosa, conjunctiva and respiratory tract. Retinal degeneration has also been documented with vitamin A deficiency.

Calcium is another important nutrient for birds. A seed diet contains very little calcium. Without adequate calcium bone development and integrity is affected. Female birds which are reproductively active on a calcium deficient diet often have egg or reproductive abnormalities such as soft-shelled egg production or egg binding. Providing essential nutrients in the proper ratio and amount is crucial as well for nutrient uptake. In the absence of vitamin D and the mineral phosphorus, the calcium is of little value. Seed diets are inherently high in fat which can lead to obesity, lipoma formation and hepatic lipidosis in susceptible species.

Fortunately most companies today provide some form of supplementation to their seed diets to improve the nutrient balance and supply the important missing nutrients. Several forms of supplementation are available. The way a diet is supplemented may affect its ability to provide the absent nutrients. Because birds' mouths are dry, with little saliva, a powdered vitamin and mineral supplement has inherent problems. Most of the powder on a seed shell or hull will drop to the floor when the bird cracks open the seed. Another way of providing a powdered supplement in the diet is to supply it in the water or on soft foods. This method also has problems. Vitamins tend to break down very quickly in an aqueous environment and when exposed to ultraviolet rays. These conditions make providing the correct dosage of vitamins and minerals difficult and potentially dangerous. The danger arises when these nutrients break down into inactive compounds in the water which increases the risk of bacterial colonization of the drinking water. Currently most manufactures today supplement the seed diet with a granule, pellet, nugget, or other form of solid supplement in the diet. If the bird consumes this added bit, it will receive the supplement. This concept, though, is based on the bird consuming this supplement and many pet birds do not ingest these supplements.

Some premium foods have been developed which provide a wide variety of dried fruits, vegetables, nuts and specialty seeds. Most of these diets contain some form of supplementation. Generally these diets are better than straight seed or supplemented seed diets because they increase the variety of food items available to the bird and decrease the number of higher fat seeds. A table food based diet is not recommended for pet birds as most people lack a balanced and nutritious diet. Table foods such as pizza, pasta and high salt items such as chips should not be fed to birds in large amounts due to the high fat and sodium content.

The ideal diet for most companion birds is a formulated (extruded nugget or pelleted) diet. There are many companies now that manufacture formulated foods for pet and zoo birds. This practice has been done for the past 50 years with canine, feline and poultry diets. A formulated diet undergoes processing to create an extruded product. This includes raw ingredients such as egg, corn, wheat, oats, amino acids, vitamins and minerals. A mash is created and cooked at very high temperatures. This extrusion process destroys most bacteria and produces a highly digestible and palatable diet. Pelleted diets are manufactured similarly to extruded diets, but at lower temperatures.

The advantage of a formulated diet is the bird receives a balances and complete balance of nutrients with a lower fat content than seed. Due to the longevity of most species, a formulated diet is the ideal option and will aid in maximizing health and reproduction for breeding birds. The greatest disadvantage to formulated diets is they require a conversion process. Birds such as budgerigars and finches may not recognize the food initially. Because these birds are small, with very high metabolic rates, they cannot go long without food intake. Caution must be exerted when trying to convert birds to these diets. A gradual conversion process over weeks to months is ideal for most birds. For most species a combination of a formulated diet (50-80%) is ideal along with fresh vegetables, fruits, legumes, and other appropriate fresh foods.

Our avian patients should have long, productive lives. Genetically they are programmed for lifespan of 10-30 years for small birds and 50 plus years for larger species. This makes the selection of an appropriate diet an extremely crucial one. The diet you recommend to your avian clients should be one which is both complete and balanced and will fit into the caretaker's lifestyle as well.

The science of avian nutrition dates back to 1890's with the discovery that chickens fed kitchen scraps developed paralysis similar to beriberi in humans. In 1896 polished rice fed to fowl and this duplicated the deficiency. The "vitamine" theory was developed in 1896 and in 1922 it was found that rickets in chicks could be prevented by Vitamin D3 in cod liver oil. Poultry were moved indoors for management and the move to indoor housing for poultry brought new problems. Chickens were no longer allowed free range to supplement their diets which led to deficiencies. "Complete" commercial rations for poultry were then developed.

Companion bird nutrition has virtually no tradition. In the last fifteen years progress has been made in the area of pet avian nutrition. As companion bird popularity increases, interest into researching nutritional needs has surfaced. There is still a relative lack of research information due to lack of funding, need to research "natural" diets, and difficulty in duplicating nutritional needs in captivity. The domestic chicken has been the model for avian nutrition and is the most studied animal nutritionally. The physiology of the chicken is similar to other avian species. Poultry nutrition information serves as framework for companion avian nutrition. Other information as to the nutritional needs of pet birds come from veterinary observations, aviculturalists' and rehabilitators experiences.

The understanding of current avian nutritional information is critical for each species. A proper diet is an essential element in the prevention of disease and maintenance of health and wellness. Proper nutrients support life by supplying energy, augmenting metabolism, transporting substances into the body, acting as structural components of the body. Essential nutrients required by body are needed to drive biochemical reactions necessary for life. The six classes of nutrients include water, carbohydrates, fats, proteins, vitamins and minerals. Essential avian amino acids include lysine, valine, methionine, phenylalanine, arginine, histidine, tryptophan, threonine, leucine, and isoleucine. Protein quality, not just quantity, is very important. The quality of the protein is determined by the amino acid profile. Seeds are deficient and lyseine and methionine are rate limiting amino acids. Clinical signs of poor quality protein include decreased growth and weight gain in hatchlings, slow or delayed molts with poor feather quality, decreased albumin/globulin ratio which lowers plasma pressure, which can lead to edema or ascites or decreased resistance to disease.

Vitamins are necessary for normal functioning of the body and regulate a variety of physiologic processes. Vitamines are divided into two classes: fat-soluble (A,D,E,K) and water soluble (B-complex, C). Many avian patients are moderately deficient in several vitamins. Deficiency of multiple vitamins can make clinical diagnosis difficult. Seed diets are deficient in all vitamins except choline and are severely deficient in vitamins A and D3.

Minerals are a very small but significant part of the avian diet. Minerals are responsible for structural integrity and egg production (calcium and phosphorus) and maintenance of acid/base and body fluid balance (sodium, potassium, chlorine). Trace or microminerals serve as components of metalloenzymes and drive a large number of biochemical reactions. Minerals should be considered as a group because of their complex interactions. There is potential for harm when imbalanced. If intake level rises above the requirement, the excess absorbed or excreted also increases. The excess absorbed can bind to other minerals (preventing their absorption). This can lead to a deficiency and a negative feedback loop.

Calcium Homeostasis in birds is a complex process and is regulated and affected by vitamin D3, plasma calcium levels, phosphorus, parathyroid hormone, and calcitonin. Intestinal absorption can also be affected by protein content, certain compounds in the diet (phylate, oxalates, phosphates), and concentrations of free fatty acids. Calcium to available phosphorus ratio should be 2:1 for proper bone development and maintenance in birds. High production laying hens may require up to 10:1 ratio. With pet birds the calcium/phosphorus ratio should be lower (2:1).

Calcium deficiency can lead to stiffness in gait, lameness, limb deviations, fractures, decreased bone density, egg binding, and/or seizures. In companion avian patients hypocalcemia is a common clinical condition in female birds on seed based diets with a recent history of egg production. Chronic egg producing birds are at greater risk for developing clinical signs associated with low blood calcium levels.

Calcium excess (levels over 1%) can lead to problems such as decreased utilization of proteins, fats, vitamins and other minerals. An excess can also lead to nephrosis, visceral gout and altered thyroid function.

Indequate sodium, chlorine, potassium in the diet rarely create distinct deficiency symptoms. Excesses may occur since they are often complexed in mineral supplements. Excessive levels result in decreased growth and appetite loss, increased water intake (polyuria), poor feathering and cartilage anomalies in chicks. Iodine deficiency can lead to goiter condition in budgerigars or other species. A mineral source provided in the cage will prevent this condition.

References

1. Hawley B, Ritzman T, Edling T. Avian Nutrition. In: Manual of Avian Medicine. Olsen Glenn, Orosz Susan. Mosby Publishing, St. Louis, Missouri, 2000, pp 369-390.

2. McDonald D. Nutritional Considerations Section I. In: Clinical Avian Medicine, Harrison & Lightfoot. Spix Publishing, Palm Beach, FL, 2006, pp 86-107.

3. Harrison G, McDonald D. Nutritional Considerations Section II. In: Clinical Avian Medicine, Harrison & Lightfoot. Spix Publishing, Palm Beach, FL, 2006, pp 108-140.

4. Stanford M. Calcium Metabolism. In: Clinical Avian Medicine, Harrison & Lightfoot. Spix Publishing, Palm Beach, FL, 2006, pp 141- 151.

5. Brue, R. Nutrition. In: Ritchie, Harrison, Harrison. Avian Medicine: Principles and Application. Wingers Publishing, Lake Worth, FL, 1994, pp 63-95.

6. Macwhirter P. Malnutrition. In: Ritchie, Harrison, Harrison. Avian Medicine: Principles and Application. Wingers Publishing, Lake Worth, FL, 1994, pp 842-861.

7. Roudybush TE. Nutrition. In: Avian Medicine and Surgery, Altman, Clubb, Dorrestein, Quesenberry. W.B. Saunders Co., Philadelphia, PA, 1997, pp 27-44.