by Dr Adrian Gallagher
The nutritional state of a bird is fundamental for good health and efficient aviary management.
In the past there has been very little scientific information on Avian nutrition, and what was available was mostly adapted from poultry as a generic feeding regime.
Feeding was an art form, with practices adopted and modified because of perceived benefits and hearsay.
Now, there is more information on nutritional practices which promote longevity and sustained reproductive success.
In the wild most birds are opportunistic omnivores i.e. they eat anything which is available e.g. vegetable, animal material, soil and mineral deposits. This is impossible to replicate in captivity. Also, this probably is not optimal nutrition as often birds live short lives and reproductive failure is common due to malnutrition.
Why is scientific information so scant?
In the last decade there have been many advances which will continue, however, it may well be decades more before we under-stand avian nutrition well.
Most scientific research has been done on poultry giving us a baseline with which to start, however, we are still learning about poultry nutrition after about 100 years of research.
Poultry are bred for production, so changes need to be made by growth studies and long-term feeding trials.
PSITTACINE DIETARY REQUIREMENTS
Tabled here are some general dietary guidelines for commonly kept Psittacine and Passerines. There are many exceptions. These guidelines are for maintenance within long-term feeding trials and may not be for optimum health.
They are not adequate for breeding, moulting, growth or disease states, but are a baseline with which to start.
I will discuss each nutrient briefly - all of these nutrients are essential for life.
This is not a nutrient as such, but is essential, which is why it is included in this section. It is required for cooling the body, for the many functions that occur inside and outside cells, for digestion and absorption of food and for elimination of wastes.
Hygiene is essential - water is easily contaminated by food and faeces and should be changed frequently. Bowls should be washed daily. "wet foods" i.e. > 20% water content should be treated the same way.
The following all have the potential to harbour large numbers of bacteria:
These can be contaminated within 4 hours in warm weather, therefore, should be removed frequently.
Dry processed diets e.g. pellets and crumbles often increase water consumption due to their dry nature, low fat and high protein levels. Expect moister droppings.
There have been very few studies on protein content for companion bird diets, however, I will discuss what is known.
Amino Acids are the building blocks of proteins. These make the DNA and RNA inside the cells.
Proteins are made up of a combination of 22 Amino Acids, 10 of which can’t be manufactured by the body and are deemed essential Amino Acids.
The usefulness of protein in the diet depends on its quality.
Factors affecting quality are:
In Cockatiels, growth studies to determine optimum Protein levels found the optimal growth and earliest weaning was achieved at a level of 20% crude protein.
10% - 15% resulted in stunting and some mortality.
5% resulted in severe stunting and 100% mortality.
25% levels gave good performance but behavioural problems e.g. meal refusal or aggression.
35% resulted in growth depression and aggression.
The only AA studies in aviary birds have been for Lysine. Best growth occurred between 0.8% - 1.2% Lysine. Less than .8% and over 2% caused growth retardation. Surprisingly no feather defragmentation was seen with Lysine deficiency in Cockatiels as is seen in poultry.
Animals and birds have no specific requirements for fats, but they do require essential fatty acids that make up the fat.
Linoleic acid is the most important. This FA can’t be synthesised in the body and must be provided in the food.
Vegetable oils are high in Linoleic acid e.g. corn, soybean, peanut - all 50%, Sunflower 60% and Safflower 70%. These FA’s are easily absorbed by binding with bile salts and broken down by Pancreatic enzymes.
Linoleic acid is required as 1% - 1.5% of diet. All seed diets would rarely fall short as there are ample fats in seeds.
Energy is necessary for all bodily functions and is derived from the metabolism of Protein, Fat and Carbohydrates.
Carbohydrates are very important because this is the only energy source the brain can use. These include starches, sugars and cellulose.
Lactose, the sugar in milk, is a poor energy source in avian species as they have no enzymes to break down the Lactose to useable chemicals.
Cellulose is the major fibre component of the diet and can’t be digested by the bird.
Fats are the most efficient source of energy, They are very easily absorbed and the method of storing energy in the body.
Birds eat to satisfy energy demands, so on a diet high in energy e.g. a high fat diet, they will eat less and therefore may not obtain the required nutrition from their diet.
These are nutrients essential for proper health and are generally only required in small amounts. I will present only an overview of their sources and functions.
There are two main groups of Vitamins:
Vitamin A - there are several forms of this vitamin all with different activities in the body. Birds don’t obtain Vitamin A from plants, but obtain its precursors, the Carotenoids. These are generally yellow/orange pigments of which B. Carotene is the most important.
Vitamin A is required for -
The liver stores Vitamin A and contains approx. 90% of the body’s Vitamin A. Excess Carotenoids in the diet do not cause toxicity as they are not converted to Vitamin A unless more is required, however, too much may cause the skin and fat to turn yellow.
Vitamin A is safe up to ten times normal requirement, however, above this level can cause cataracts and bony deposits.
Deficiency in Vitamin A is the most common Vitamin deficiency we see as dry seed is low in this vital vitamin. Birds on a high dry seed diet must be supplemented with Vitamin A or Carotenoids.
Vitamin D - there are two forms of this vitamin in the body:
Vitamin D3 is 30 to 40 times more potent than Vitamin D2 so Vitamin D2 is generally disregarded.
Vitamin D3 is synthesised in the body by exposure to U.V. light. 11 - 45 minutes per day of unfiltered light was enough to provide adequate Vitamin D3 to growing chickens.
Vitamin D3 precursors may be excreted by the preen gland and spread over the feathers. After exposure to U.V. light and conversion to Vitamin D3, these are re-ingested.
Vitamin D3 maintains the levels of Calcium in the body. Low Calcium, high Phosphorus diets will precipitate Hypovitaminosis D (Rickets).
Birds on low Calcium diets in sunny flights showed no signs of Rickets, yet birds on the same diet in shaded flights showed this disease. Birds in shaded flights may require added Vitamin D3.
Signs of deficiency in Vitamin D3 are similar to those of Calcium deficiency -
In young growing birds:
An excess of Vitamin D3 produces calcification of other organs especially the kidneys which can lead to Visceral gout and death. Macaws appear to be susceptible to high levels of Vitamin D.
Cockatiels given 4000 iu/day i.e. 4 times the requirement had high egg production for one year then a decreased reproduction rate. X-rays showed calcification of the kidneys. Males were less affected. All signs of excess disappeared when Vitamin D levels returned to normal.
Vitamin E - There are 8 forms of Vitamin E found in plants primarily in the germ and are most common in oily plants.
Vitamin E is an antioxidant which prevents the fats in the body becoming rancid. It works together with other minerals especially Selenium.
Vitamin E is absorbed freely in the bowel but requires proper liver and pancreas function for digestion. It is stored in the liver and in plasma in blood.
Plants high in oils provide adequate Vitamin E, but rancid fats e.g. wheatgerm oil left in wheat will use up this vitamin from the body and create a deficiency.
Vitamin K - this is the first of the water soluble Vitamins and is required for blood clotting. It is found in green plants and is also produced by bacteria in the bowel. Natural deficiencies have not been seen.
Deficiencies occur with Coccidiostates and long term antibiotic treatment which kill off the bacteria in the bowel.
Thiamine (B1) - This is freely available in most foods and requires constant uptake and is not stored in the body.
Deficiencies occur for a number of reasons:
This is uncommon in seed eating birds as seeds have adequate Thiamine but it can occur in carnivorous birds fed a sole meat diet or whole fish.
Honeyeaters around the Sydney area develop Thiamine deficiency in winter due to a change in diet to low Thiamine foods. In normal circumstances they would migrate, however, because of a high incidence of nectar bearing flowers but low pollen availability, and to some degree, well-meaning people feeding ill-balanced diets, they stay put instead.
Response to Thiamine injections is rapid, often within minutes.
Riboflavin (B2) - Occurs in plant and animal tissue especially eggs.
Deficiencies in chicks cause:
Deficiencies in adult hens cause:
Excesses don’t occur as this vitamin is readily excreted.
Niacin Occurs in all foods but is poorly absorbed from plants. Very high in animal products. No storage of this vitamin occurs in the body.
Deficiencies shown are non-specific:
This hasn’t been described in Psittacines.
Pyridoxine (B6) - occurs in plant and animal material and very little is stored in the body.
So far, this has been unknown in Psittacines.
Cockatiels raised on a diet deficient in Pantothenic Acid failed to grow contour feathers on chest and back and died at 3 weeks of age.
Biotin - is widely distributed in foods in low concentrations. It may be absorbed from bacteria production in the large bowel. Biotin is stored in the liver but is slow to be mobilised if needed.
Mycotoxins / fungal toxins in the diet affect Biotin up-take.
Deficiencies are as per Pantothenic acid.
Folic Acid - is common in foods and is produced by bacteria in the large bowel. This is important for AA metabolism and cell division.
Enzyme inhibitors are present in some foods and affect the uptake of Folic acid e.g. cabbage, oranges, beans, peas, Brewers yeast, however, these inhibitors are destroyed by heat treatment.
Deficiencies may occur with long-term antibiotic therapy and can show as:
Vitamin B12 (Cyanocobalamine)
This vitamin is produced by bacterial activity, and there is very efficient storage in the liver and muscle tissue.
Choline - whose natural sources are common, usually as Lecithins. This vitamin is found in all tissues of the body. Double the required amount produces signs of toxicity.
Cockatiels on a low Choline diet produced unpigmented wing and tail feathers but no bony deposits.
Vitamin C - is not required by most birds, only by highly evolved fruit eating birds such as the Willow Ptarmigan and Red Vented Bulbul. It is usually easily manufactured by the liver and is also found naturally in fruits, vegetables and animal products but not in seeds.
Absorption occurs in the small intestine. Less absorption occurs the higher the level of Vitamin C in the diet. This vitamin is required in the body as an antioxidant and also for Collagen production. Although not essential for Psittacines or Passerines, benefits have been shown by its addition to the diet during stressful periods e.g. moulting, egg production, growth, transport, disease.
Vitamin C is best given in fresh foods as it is unstable in manufactured products. It has also been shown to increase Albumin quality and eggshell thickness resulting in higher hatchability.
Deficiencies have not been seen in companion birds.