By Rick Kleyn, MSc (Agric), Nutritionist, Avi-Products
Vitamin and minerals make up only a small part of the average avian diet, yet they play a key role in the well being of the bird. This is probably most true in the case of breeding birds, where deficiencies in these key nutrients will cause a reduction in fertility in both males and females, a reduction in hatchability as well as reduction in the viability of the progeny. In this the first of two articles on the subject, mineral nutrition in breeding birds will be dealt with.
It is well documented that mineral deficiencies will impact on birds in many ways. If a diet is deficient in one of these minerals, it is unlikely that birds will breed in a normal manner. On the other hand, an excess of a mineral can be even more debilitating and can easily lead to the death of a bird, as is evidenced by sodium (salt) toxicity.
In broad terms mineral nutrition is characterised by a number things. Firstly, there is a complex set of interrelationships that exist between the different minerals in the bird. This is largely as a result of the fact that in order for minerals to be absorbed by a bird, they first need to be transported across the gut wall, mostly by what is know as a carrier protein. The different minerals are believed to compete for these proteins, which is why an excessive level of a mineral can and does inhibit the absorption of another. Perhaps the best know of these interactions is that exists between calcium and phosphorus.
The second outstanding feature of mineral nutrition is that birds only tend to absorb what they actually require. This is well illustrated by figure 1, which shows how zinc absorption drops off after a certain level in the tissues is achieved. Clearly, the percentage of Zinc absorbed from the diet is dependent on the level of mineral in the diet. As similar pattern is know to exist for most minerals in the diet.
All animals have bodily reserves of minerals, which can be built up and then drawn upon in times of need. Mineral toxicities occur when these “stores” exceed normal levels, and the manner in which this occurs is dependant on both the levels in the diet and the duration that they are fed the diet. The key “upper” and “lower” for minerals for chickens are shown in table 1. It should be remembered that this list is not comprehensive, and nutritionists can’t be sure if the minimum levels for chickens would be adequate for all classes of bird. We know for example, that turkeys have far higher mineral requirements that other types of poultry, and there is a possibility that diets formulated for chickens may well be deficient in one of the key minerals for other species.
Figure 1: Effect of increasing dietary intake on true absorption of zinc in Japanese Quail.
Table 1: Minimum and maximum tolerable levels of minerals in chicken diets (all in ppm) (Source, NRC, (1994)).
It is important to remember that not all sources of a mineral are equally available. In the first instance, animals can simply not digest some mineral sources. For example, nearly two thirds of the phosphorus contained in plant material occurs in phytate form. Animals do not posses the enzymes know as phytase required to break down these molecules, so all phytate phosphorus simply passes through the bird without even being digested. Secondly, not all forms of mineral are used in the body with the same efficiency. As an example, Iron Oxide (which we know as rust) can’t really be utilised by birds at all. Iron Sulphate is a far better source of iron, while it has been shown that the organic forms of iron, such as iron proteinate are the most available source of all.
It should be borne in mind that in the wild, birds will select dietary items so as to meet their requirement for a specific mineral. Wild ducks have bee shown to increase their intake of animal foods, particularly crustaceans, at the onset of the breeding season so as to increase their bodily reserves of calcium.
From a breeding bird perspective, it is important to appreciate that the mineral status of the laying female determines the amount of each mineral transferred to the egg and the mineral stores of the hatchling. In the case of precocious birds (birds that are fed by the parents), parental diet is of great importance in maintaining the mineral status of the young.
The most important minerals are what are known as the macro minerals (Calcium, Phosphorus, Sodium and Potassium). These are likely to have an impact on the general viability of the breeding flock, and any deficiency will manifest itself in clinical symptoms fairly quickly. The micro minerals on the other hand (Zinc, Copper, Manganese, Selenium and others) are less likely to play “visible” role in breeder flock well being, but they play a vital role in breeding results as will be seen later.
Of the macro minerals calcium and phosphorus are the elements of specific concern. These two minerals are essential for skeletal integrity, various regulatory roles in the body and eggshell formation. They share a carrier mechanism (a metaloprotein) for normal absorption, which only functions normally in the presence of Vitamin D3. If an excess of either calcium or phosphorus occurs in the diet, the uptake of the other is severely inhibited. For example, if too much limestone (the traditional calcium source) is added to a diet it will lead to an effective phosphorus deficiency. By contrast, too little calcium will also have a direct impact on the bird in that deficiency symptoms will occur. There are a variety of symptoms, which would include rickets, soft bones, muscular problems and perhaps most importantly soft shelled eggs.
Calcium deficiency is an extremely common problem in pet birds. Not only are the seeds which are often fed deficient in calcium, but the fatty acids present in the oil of seeds such as sunflower seeds combine with calcium to form insoluble soaps, even further decreasing its absorption.
Fortunately for most aviculturalists the bird is able to build up a calcium reserves within the medullary or soft part of the bones. This is complicated somewhat by the fact that small birds lay proportionally larger eggs. In addition, precocial species generally lay larger eggs than similar sized altricial species. It is estimated that there is enough calcium in the birds own body reserves for a clutch of 10 eggs in the case of a hen, but only for about 5 eggs in the case of a Zebra Finch. For larger clutches, some additional calcium is required in the diet.
If, for example, you feed Avi-Plus Parrot and Parakeet at the correct levels (i.e. at 25% of the total diet) you should not have to add any additional calcium or phosphorus to the diet as the product contains adequate levels of these minerals. If on the other hand you reduce the proportion of the product in the diet, you may well need to supplement it in some way. Feeding high levels of calcium alone (in the form of additional limestone) may in fact have a deleterious effect on the bird, as it is essential that Calcium and phosphorus be offered to birds in the correct proportions. We at Avi-Products were mindful of this when we developed Avi-Cal, and if you fell that you simply have to boost the calcium status of your birds, please use this or another balanced product.
Overfeeding of calcium can and does occur under practical avicultural conditions. For example, commercial layer pellets, which are widely fed to pheasants and waterfowl, contain in excess of 3% calcium. Whilst this is perfect for breeding adults, it is far too high for young chicks, and if care is not taken to offer the chicks a separate diet, rickets and other problems may well occur.
The one way of overcoming the overfeeding of calcium is to allow the birds free choice. Rather than mixing any supplement into the diet, offer it separately.
It is beyond the scope of this article to go into detail on each of the micro minerals fed too birds. However, there are a few well-documented problems that occur in birds when they do not receive adequate quantities of minerals, and these are discussed below.
The enzyme, tyrosinase, which is responsible for the production of melanin, is copper containing. This induces pigmentation defects of the eggshell, and eggs from copper deficient females are often infertile and have defective shells due to defective collagen in the shell membrane. Zinc is an all-important mineral. Diets that are zinc deficient cause a sharp drop in food consumption. This in turn cause impairs the number of eggs the female will lay. In quails and pheasants, maternal diets that are deficient in zinc give rise to chicks that are weak and have laboured breathing.
Many birds in captivity do not have access to soil and they can become iron deficient. In some species this can be seen in a reduction of the colour of red and black feathers. Iron-deficient females lay eggs that undergo embryonic mortality, due to anaemia in the later stages of development.
A deficiency of phosphorus will lead to embryonic mortality during the last trimester, whereas a deficiency in manganese, particularly in the case of the diet of the adult birds in the case of proceal birds will lead to skeletal abnormalities such as slipped tendon, which leads to skew legs.
Other minerals have been shown to have a direct impact on the humoral immune system of the bird. For example, it is know that zinc is required for good progeny immunity. Manganese is also implicated in immune response. In recent work in farm animals it has been shown that by boosting the selenium, which is a natural anti-oxidant, the immune status of the progeny is improved.
How minerals effect male fertility is unclear. It is know that zinc boosts the production of viable semen in male birds and other animals. The anti-oxidative effect of selenium has also been shown to boost male fertility in poultry. Adding selenium to the diet is not something that should be “tried at home”. The quantities used are measured in parts per billion but toxicity occurs at levels as low as 5 parts per million, thus making selenium the most toxic of all minerals. It is probably safe to assume that a deficiency in any of the minerals in likely to have a direct impact on sperm production and motility.
In order for the bird breeder to benefit from this latest research regarding selenium’s impact on chick viability as well as it’s benefit on male fertility, all Avi-plus products have now been supplemented with a highly available (and safe) source of organic selenium.
The Avi-Plus range of products all contains adequate levels of both the macro and the micronutrients. These levels comfortably exceed the estimated minimum requirements established for poultry, and would be adequate for all pet birds. However, the mineral levels nowhere near the dangerous or maximum permissible levels that have been determined for poultry. If Avi-Plus products are fed in the diet in the recommended manner, there is little likelihood that the bird breeder wills ever experience fertility problems as a result of a nutrient deficiency. The minute any balanced product is diluted using full fat soya or any other ingredient, the levels of minerals that the birds consume may well drop below the optimum and the breeder can expect sub-optimal fertility and hatchability.
Micronutrient Nutrition of Breeding Birds: Part 2, Vitamins
In the previous article in this series I discussed the importance of minerals on breeding birds. In this issue the Vitamins mill be dealt with. Vitamins are truly micronutrients and their inclusion in the diet is measured in parts per million or less in the final diet. They are organic substances that are metabolically essential to the bird and the exclusion of a single vitamin from the diet can and does have dramatic effects. Mostly birds are unable to synthesis their own vitamins as they lack the necessary biochemical pathways. For this reason dietary vitamins are particularly important in their role in fertility, hatchability and chick quality.
Before I go into a lot of detail about specific vitamins, there are some general aspects of vitamin nutrition that need to be discussed.
1) Vitamins are split into two distinct groups, the fat-soluble vitamins and the water- soluble vitamins. The fat-soluble vitamins include the following; Vitamin A (Retinol), Vitamin D, Vitamin E and Vitamin K. All of these vitamins require some body fat for their metabolism. They are often present in plants as pro-vitamins, which are quickly converted to the true vitamins in the body of the animal. They are easily stored in fat cells and any excesses are excreted through the faeces.
The water-soluble vitamins are mainly needed for normal energy metabolism in the body, although we are becoming increasingly aware that they also play a role in protein metabolism. The important vitamins in the water-soluble group are as follows; Vitamin C (Ascorbic acid), Pyridoxine (B6), Thiamin (B1), Riboflavin (B2), Biotin, Pantothenic Acid, Folic Acid, Niacin, Vitamin B12 and Choline.
Apart from vitamin B12 birds are not able to store any of the water-soluble vitamins in their bodies, and therefor require all the water-soluble vitamins in their diet daily. Vitamin C is the exception in that most species are able synthesise it themselves. When a feed contains excess levels of the water-soluble vitamins they are excreted in the urine. For this reason, it is important that birds receive the correct level of these vitamins on a daily basis. A single large dose once a week will only end up on the floor. It is precisely for this reason that humans are advised to take a vitamin tablet every day.
The significance of the difference between the classes of Vitamins is very clearly illustrated by work published by Prof. Steve Leeson form the University of Guelph in Canada. In this experiment, single vitamins were deleted from the diet of breeding hens, and were then reintroduced 15 weeks later. It is important to note firstly just how dramatic an effect the deletion of a single vitamin can be, particularly the water-soluble vitamins. Secondly, it is of interest that fertility returned to normal after 4 weeks, implying that no permanent damage was done.
Table 1: Hatchability of eggs produced by caged breeders fed diets devoid of supplemental vitamins (% fertile eggs)
2) All vitamins, be they natural or synthetic are subject to degradation (oxidation) over time. High temperatures, UV radiation (sunlight), oxygen and moisture exacerbate this. Keeping food refrigerated or frozen helps, but research has shown that even the vitamin levels in frozen meat drop with time. It is essential therefore to use fresh vitamin sources at all time.
It is true that the ingredients we use to feed out birds do contain vitamins. The levels vary considerably from batch to batch as influenced by the growing conditions of the crop. It is also true that not all of the vitamins that occur in natural ingredients are available for use by animals. A good example of this is that almost all of the niacin found in cereal grain is unavailable to birds as it is bonded to other components in the form of niacytin. For this reason, nutritionists tend to ignore the vitamins that occur in natural ingredients, and add the entire requirement in terms of supplementation.
3) Determining the level at which any animal’s diet should be supplemented with vitamins is a matter of debate amongst nutritionists. It is known that issues such as life stage (i.e. breeding) stress, parasite infestation, and infectious diseases also greatly increase the bird’s requirements. In addition, manufacturing processes such as extrusion and the time the product is likely to sit on a shelf are also important. In figure 1, the process that is followed is graphically illustrated. The NRC figure is the standard used by nutritionists to indicate the level at which deficiency symptoms no longer occur.
Figure 1: Optimum vitamin nutrition for animals (after DSM)
NRC Recommended level
4) It is important that we realise that as with the minerals, it is possible to feed birds too much. In work done in America on Bobwhite Quail, varying levels of vitamin A were offered to breeding birds. The results of this work are shown below.
Figure 2: Effects of vitamin A on survival and reproduction of captive Bobwhite Quail
It is of particular interest to note that for all parameters measured, a steady response was observed until a feeding level of about 8000 IU/kg was reached, at which point little improvement was noted. Perhaps of more interest, was the fact that a depression in hatchability was observed when levels exceed 12000 IU/kg.
Average Animal Response
In the case of breeding birds, there is a very clear relationship between the dietary vitamin levels and their concentration in the eggs of chickens. All of the vitamins have an impact on reproductive success and it is beyond the scope of this article to address the effects of each of the vitamins in turn, however there are some important issues that need to be raised. If you would like to do more reading on this subject, “Comparative Avian Nutrition” by Kirk Klasing covers the topic in great detail.
Vitamin A is the most likely vitamin to be deficient in either captive or wild birds. Plants do not contain Vit A itself, but rather a variety of carotenoids, which are the precursors of Vit A, and the levels that exist in most plants are extremely variable. High levels of Vit E (a natural anti-oxidant) have been shown to improve chick quality and boost humoral immunity. However, it has been shown that high levels of Vit E in the diet inhibit Vit A uptake and that if the Vit A levels are reduced, the uptake of Vit E improves.
Birds are able to synthesis Vit D in the presence of UV light. It has been shown that 15 minutes of normal sunshine per day will enable a laying hen to produce adequate amounts of Vit D. It is only under artificial lighting conditions that there is insufficient UV light and the bird needs to be supplemented.
Each of the B vitamins is essential to the production of healthy young, and it can be seen from table 1 just how sensitive to reduced levels of these vitamins birds are. Riboflavin (Vit B2) deficiency is know to result in classical curled toe paralysis, while a deficiency of biotin can lead to abnormal beaks (know as parrot beak) and deformed down (club down).
The entire Avi-plus range of feeds contain vitamin levels that are all well into the “optimal” range of supplementation. We have taken the losses in extrusion, together with a longer storage time than normal poultry feeds into consideration. As with is the case with the minerals, if you feed Avi-plus products in the recommended manner you will never need to supplement your diets with additional vitamins. If the inclusion of Avi-plus is reduced through adding additional seeds to the mixture, then there is a chance that you may dilute the amount of vitamins fed to your birds on a daily basis. If our products are mixed with any other ingredients we are no longer able to guarantee the adequacy of the diet.
The supplementation of avian diets is something that needs to be done with care, and it is often problematic in the case of captive animals and birds, many of whose lives are shortened by over-supplementation of nutrients. The most common toxcities that occur are Vitamin A and Selenium. Both of these nutrients accumulate in the body and compromise the animal and its immune system. If too much vitamin A or selenium are consumed, the animal could die of toxicity. The interactions of minerals and vitamins alone would frighten most individuals if they had the facts at hand! Some animals cannot metabolically handle the additions, where as others cant.
Toxicities, and deficiencies for that matter, may arise for a number of reasons. Firstly, care should be taken not to use “too” many supplements all doing the same thing. Not only is the chance of toxicity increased, but also if both products are deficient in a nutrient, they will not prevent a deficiency from occurring. Secondly, it is essential that some form of accurate measurement be used when using a supplement. A “pinch” is simply not good enough. It is for this reason that products such as Avi-Products Avi- Sup Twin Pack are sold with the very clear recommendation that 5 g be used per kg of soft food.
There is an important aspect that needs to be added to the discussion on vitamins and mineral supplementation. This is best illustrated by an experiment that was conducted by Angel and Balsam in 1996. These workers fed 123 pairs of parakeets, four different diets. These were complete breeder diets containing 13, 18 and 25 percent protein, and a control diet, which was a mixture of seeds (white millet, canary seed and hulled oats), supplemented with both vitamins and minerals. The complete diets were identical apart from their differing protein levels and were supplemented with vitamins and minerals in the normal way. The breeding results that were achieved are shown in the table 2 below.
Table 2: Breeding performance and growth of parakeets.
The most important figure in table 2, is the number of babies weaned per pair of parakeets. In scientific terms we would say that there was no significant difference between the 3 different complete diets and that a complete diet containing 13.5% protein was adequate and allowed the birds to achieve their normal production. The supplemented seed mix, containing 13.4% protein resulted in a highly significant reduction in performance. Seed mixtures tend to be deficient in amino acids, and despite the fact that vitamin and minerals were supplemented, this did rectify the shortfall. The lesson to be learned from this experiment, is that if the diet is fundamentally unsound (imbalanced), no amount of supplementation with vitamins or minerals will help