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Avian Nutrition: Trends and Philosophies
Mark Hagen, M.Ag.
Optimum nutrition can be achieved with many different diets. However it is not easy and understanding some basic principles of the pro and cons of each food item as it relates to vitamins, minerals, proteins and fat is important when trying to make up a mixture of foods. Wild animals and birds are shown by their parents the right combination of sometimes very limited types of foods to meet their requirements for flight, growth, reproduction and living! These wild food items have been selected through thousands of years of evolution. In captivity they are under different conditions and eating different foods and we expect them to select the best combination immediately. But it is not necessarily better to feed what birds eat in the wild to those in captivity. Many plants in the wild contain secondary plant compounds or are very low in many essential nutrients. For instance the feeding of clay type neutralizing mineral supplements as found in the cliff deposits of Peru is not necessary to a captive Macaw eating foods grown for human consumption. Some Breeders have a romantic notion that captive diets which are complicated, labor intensive, using expensive ingredients are the most nutritious. Yet it is possible to feed easy to prepare, cost efficient diets which do not compromise proper levels of essential nutrients.
Rather than explain each essential nutrient such as vitamins, minerals etc. and what their role is in the physiology of birds, I would rather discuss how to get these nutrients into birds at optimum intake levels. Seeds were commonly the main staple food fed to pet birds and parrots. Some birds even breed on them. However optimum nutrition was rarely achieved and birds did not lay complete clutches, or live as long as they might have. The trend in America is to feed more legumes, pasta and formulated diets to Parrots and to significantly if not totally eliminate oil seeds from their diets. At least twelve different companies now sell formulated processed diets and my estimate is that at least half the breeding Parrots are being fed such commercial formulas rather that seed mixtures. Seeds can work well when properly supplemented and when fed at low levels forcing the bird to eat his veggies and other supplemented foods. Fruits and most vegetables make a good carrier for a water soluble vitamin/mineral supplement to add to a seed based diet. They do not contribute much themselves as they mainly contain high levels of water, some fiber, a few vitamins and some minerals in the case of dark leafy types. I personally do not like them because of sanitation, the work and cost involved in preparing them and cleaning up the wasted mess often left behind after birds have picked through them.
The most dramatic nutrient problem with seed based diets is not their deficiencies, which can be met with supplements, but their excesses of fat which can not be removed prior to feeding. Fat levels in the three most commonly eaten seed kernels are so high that these seeds are referred to as "oilseeds". Although safflower is a smaller and less palatable seed than sunflower, its fat content is, in fact, higher than sunflower. Birds may not like the bitter taste of safflower and tend to eat a larger variety of seeds when eating a diet based on it. High fat intake results in small compact stool and low water intake since water is a by-product of fat metabolism. Formulated diets produce much larger stool, especially lower fat pelleted diets where birds also drink more. The correct balance of calories in the total diet versus the needs of energy and growth by the bird is an important topic. Colder environments, larger cages, free flight cages and breeding activity, does require more energy. But the sedentary life of most cage birds together with the constant availability of food inevitably leads to over eating. This along with the consumption of oilseeds, nuts and other high fat foods limits the eating of other more nutritious foods, which includes formulated diets. Certain higher fat levels should not be considered totally bad. Even eight to twelve per cent fat in a formulated diet, is still one fifth the levels found in oilseeds. Sprouting seeds can reduce the fat levels and add some vitamins. The problem with sprouting is the risk of fungal contamination such as candida and the space and time needed to prepare the sprouts.
The caloric density of a diet is important because this is what determines how much food the bird will ultimately eat. Thus the energy level influences how much vitamins, minerals and protein the bird will receive on a daily basis from the ingested food. More pelleted food needs to be eaten by birds to maintain their weight, in fact almost twice as much as high calorie seed kernels.
Fat has more than twice the energy value per gram than protein or carbohydrates and this accounts for the energy differences. The cost of feeding a bird is not based on the price per kilogram of food but the price per kilo-calorie of digestible energy. Extruded foods are able to incorporate more efficient fat levels into the texture of the "kibble". Higher digestibility and slightly higher energy values are the trends in producing a very economical diet with excellent health maintenance. Pellets are made by adding a little steam and a lot of pressure to the ground up dry "mash" and squeezing it out of a large steel die. This process is more commonly used by farmers to produce low cost chicken and pig feed. Extrusion processing uses higher moisture cooking and is more commonly used for Human and Pet Foods. Much higher cooking temperatures are achieved although only for a very short period, but long enough to kill most pathogenic bacteria (which may be in some raw ingredients), gelatinize starches thus increasing digestibility and incorporating a larger variety of ingredients into the cooked matrix of the resulting kibble. There is no doubt that most extruded foods are more palatable than the same formula pelleted. Also pellets have a tendency to produce a fine powder when the bird bites into them leading to wastage. Extruded kibble tends to break into still edible pieces rather than explode into a powder.
The quality of protein, that is its amino acid balance and digestibility,
is as important as is the total level of protein in a diet. The larger
the number of different grains, legumes (beans), nuts and other protein
sources the better the balance of amino acids will be. So besides the
obvious palatability advantages of this mixture of ingredients, benefits
to protein quality also occur. The different amino acid profiles of these
various protein sources complement each other, resulting in a premium
protein of high biological value. Research at UC Davis found the amino
acid-lysine requirement of Cockatiels to be 0.8% and a total protein requirement
of 20% on the dry matter basis of the diet. This is very similar to the
Broiler poultry requirements, which we could then use as a starting point
for estimating parrot growth requirements. When comparing these estimates
for amino acids to the levels found in oilseeds it appears that all three
are low in lysine and methionine/cystine. Feather protein contains a higher
level of cystine and thus during maximum feather growth in a nestling
or molting in an adult, the relative requirement for cystine increases.
Parrots on a oil seed based diet develop poor feather structure and this
may explain it. Supplementing seed diets with lysine and methionine which
birds can convert to cystine greatly helps in beautiful
Many people look upon formulated diets as being monotonous and state "how could my bird live on one food alone". Yet some formulated diets contain a larger variety of ingredients and protein sources than what some birds end up eating out of an oil seed based diet. Some concern has been expressed over birds receiving too much protein and thus stressing nitrogen excretion organs (a by-product of protein metabolism). Remembering the total amount of protein consumed by the bird is dependent on the energy density of the food, we must therefore divide protein by the calories to get a meaningful comparison of various diets. This area of optimum protein to energy levels still needs a lot of research. It may be possible and better to feed relatively lower protein levels during much of the year. The availability of higher protein foods probably stimulates wild birds to breed but because we may be feeding diets with too high a base level, adding more nuts or switching to higher protein processed food does not achieve the same level of stimulation as in the wild. Such careful changes to nutrient levels can really only be achieved with properly formulated diets where the bird has little chance to select out a different level.
As mentioned, the high calorie nature of oil seeds limits their consumption and thus lowers the amount of amino acids available for growth of new feathers, muscles, etc. So, although oilseed kernels have a higher concentration (%) of protein, birds do not receive enough protein, which further explains the poor feather growth in birds eating oilseed based diets. And conversely, birds may be processing too much protein on pellet type diets as a by-product of having to consume more of these diets to meet their energy needs. The US based NRC uses the concept, of expressing required nutrient levels based on certain dietary energy values, for all animal nutrient requirement publications.
Fiber levels in seed kernels are much lower than what is declared on analysis statements on bags of mixed seeds. Since birds hull off the husks of seeds and nuts, these high fiber shells are not eaten by the birds but must be included in the whole seed bag analysis for packaging. This results in an under estimation of protein and fat and over estimation of fiber rendering the nutrient information on bags of seed meaningless. Selection by birds of the high calorie seeds and rejection of lower fat grains (which would balance out the fat) results in malnutrition and obesity. Formulated diets balance fiber with other nutrients in a pre-mixed kibble where birds cannot select out the higher fat ingredients. The mess around cages from high fiber hulls, a negative aspect of bird keeping, is also eliminated with a formulated diet. Food used as a play toy is wasteful and unhealthy. Giving wood, rawhide and rope chew toys is far better for the long-term health of birds.
Optimum vitamin levels are harder to determine and can easily be missed in the bird. Deficiencies of several vitamins may result in poor reproduction. Resistance to disease and general health are difficult to measure. How much more Vitamin A, E or C should be added to a diet before the cost is wasted or the bird receives too much? One way around this is to add forms of the vitamins that are safer. Pre-vitamin A or Beta-Carotene is an example, which the birds can then convert to vitamin A as they need it. Vitamin C may be required during stress or in babies and is a very fragile vitamin that breaks down quickly in foods. By using stabilized or chelated forms gives greater assurance the levels that are added are going to be received by the bird. One company warned users of their Vitamin E supplement to take it away from male Cockatoos once breeding began as they related excess E to aggression in male Cockatoos. Not having enough Vit E will lead to infertility but adding more than that required does not necessarily mean birds become violent to their mates! Adding more Vit E than that required by the bird will help act as a natural anti-oxidant in formulated diets, protecting fats from becoming rancid and other vitamins from being destroyed.
Excess Vitamin D3 has caused more problems in formulated and attempts at supplementing cafeteria style diets than any other vitamin. Yet this may be more due to the fact that the result, excess calcification of soft organs such as kidneys, could be easily found upon histopathology. An Avian Nutrition Committee was formed by the US based Association of Avian Veterinarians (AAV) to look at issuing some guidelines on nutrient levels in maintenance bird diets. I had the honor to be part of this process and one of the most important recommendations that we made was that Vitamin D3 levels should not be higher than 2,000 IU/kg of a Parrot's diet (Gross energy diet range 3200 - 4200 kcal/kg). There is no reason why we should see baby macaws die of a painful Vit D3 toxicity, even though some commercial interests may not want such open exchange of private food research data. (see Feed Management, Watt Pub., Feb 1998, Vol 49 #2)
Common problems in birds on seed based diets are poorly calcified eggs and egg binding, weak bones, thyroid and muscle contraction problems. These are all related to the lack of several minerals in seed kernels. Simply producing a supplement for seed based diets that contain a little of each essential mineral is ignoring the fact that some minerals may already be at high enough levels in seeds. Potassium and iron are two minerals which are found at good levels in seeds. Too much iron supplementation may cause liver disease in some types of toucans, mynahs and other softbills. A closer look at each mineral deficiency is needed to prepare a proper supplement.
It appears that phosphorous levels in most grains and oilseeds are sufficient. Some of the phosphorous is unavailable to the bird as it is bound up with phytic acid. The ratio of phosphorous to calcium needs to within a range of about 1:2, that is twice as much calcium versus phosphorous. Most mineral supplements for birds contain this ratio but, when combined with high phosphorus, low calcium seeds do not result in the correct dietary intake. Calcium levels in oilseeds are so low that African Grays, after just a few years on seed diets, may develop muscle tetany or other problems. These Grays would need emergency veterinary calcium supplementation as they have difficulty utilizing bone sources. Unfortunately, excessive calcium and its related nutrient vitamin D3 became a problem as breeders oversupplemented diets. In rapidly growing babies, calcium is deposited in soft tissue such as kidneys. Organ failure would result, illustrating the point that home made mixtures of food can be dangerous. Formulated diets that have strict quality control on nutrient levels are safer for birds especially with inexperienced pet owners.
Psittacosis is still a problem with some species but can be eliminated with long term feeding of a medicated pellet. This zoonotic disease can be found in sub-clinical carriers such as cockatiels. A pet store in New Jersey last year was sued by a customer who got sick from the bird they had bought there. Under USA product liability laws the customer was able to claim the pet store sold a defective product which caused him personal injury. The insurance company of the pet store settled out-of-court for $400,000.US. At HARI we have eliminated carriers of Chlyamidia, which causes Psittacosis, by feeding a formulated diet with a1% chlortetracycline premix added to the formula for 60 days. Other formula modifications need to be done such as higher anti-fungal levels (calcium propionate) and lower calcium levels. My point here is that formulated diets are our best answer to eliminating this disease from our aviaries. Adding drugs to drinking water is not the best way to eliminate this disease from a carrier.
It is true that we are at the early stage of understanding the nutritional and behavioural needs of captive birds. But we will only learn more about their specific needs for fat, proteins and vitamins if we know the composition of the diet we are feeding them and what the birds get from it. This is almost impossible to figure out when birds can pick through cafeteria style feeding methods. All the wasted food would have to quickly be collected and analyzed and subtracted from the presented food; the difference being what the bird ingested. In the 1980's when I was working on my Master's degree I tried this and could not come up with accurate numbers there was just too much waste. I was however able to set up a unique food hopper, feed shelled sunflower, and collect the pieces of kernel wasted by the birds, in this case Goffin's Cockatoos. The metabolizable energy value of sunflower seed kernel in these caged Goffin's was 6,201 + 282 kcal/kg when determined in an ad libitum total collection trial and 6,094 + 86 kcal/kg when determined by force feeding with total collection. The average daily existence metabolism for the Goffin's under caged maintenance conditions was 48 kcal/day/bird or 185 kcal/day/kg of bird. This is about 2.2 times the basal metabolic rate predicted from formulas. Knowing the energy needs of a bird and the energy value of a diet will ensure that enough of a nutrient is added or supplemented to that portion.
There are several different ways to switch birds to a formulated diet. Slowly decreasing the ratio of seeds to pellets makes for a messy conversion as the bird seeks out its oil seeds and throws the pellets on the ground. We have found it is better to use multiple bowls and allow the seed bowl to empty each day by feeding a lot less and always making sure the pellet bowl is full. Adding warm water and mixing in some sunflower kernel to the formulated diet improves the conversion. Moist food is more palatable to many birds, but spoils very quickly and should be replaced often, even twice a day. Slowly switch to the dry form once conversion has occurred. Questions of conversion rarely come up in America lately because most baby parrots sold to the pet trade are weaned onto formulated diets. We have found that this is easier than weaning to seeds supplemented with all kinds of soft foods. If the requirements for excellent growth and featheration are met then it would be difficult to say that the formula is not complete. So with tens of thousands of parrots having been raised on these diets we can worry less about knowing what the precise minimum requirement for each nutrient for each species of bird actually is.
Some ingredients used in formulated diets have been questioned lately. While soybeans are an excellent source of protein, in the raw state they do contain anti-nutritional factors which interfere with protein utilization. These are however destroyed and inactivated during processing. Science does not have all the answers, yet forces us to look at issues and questions in a structured manner (the scientific method) which allows some conclusion to be reached. Too often breeders change something in their husbandry and equate success or problems to that change. There are many variables which can influence failure or success; weather, sub-clinical (undiagnosed) disease, experience, stress and others. In order to more accurately judge a new supplement or food it is important to minimize these other factors. One way to more fairly judge a product or ingredient is to only give it to half the number of pairs of a species and to treat the other half as a control group to compare to. Keep an open mind and always question yourself "is there a better way?"
Check out the HARI web site at http://www.pubnix.net/~mhagen for references related to Avian Nutrition.