Minerals in our bird's nutrition !

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.

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.
An article by By Rick Kleyn, MSc (Agric), Nutritionist
source :. http://spesfeed.com