Deficiencies of essential nutrients can arise for one of two reasons. Either the nutrient is not present in the food that the animal or bird is consuming, or the animal or bird has a physiological maladjustment preventing it from being able to utilise the nutrient, although it is available in the feed. This is known as a metabolic disease.
Essential nutrients are required for the bird to live, grow, reproduce and produce. In deficiency situations it is often difficult to know which nutrient is causing the problem. Usually feeding the nutrient as a supplement will give a quick response.
The balance of nutrients is also important eg Calcium (Ca) and phosphorus (Phos) or Copper and Molybdenum have to be present in certain ratios to each other. An excess of one will lead to a depletion of the other. Many vitamins, minerals and amino acids are pre-cursors, necessary for the production of another nutrient eg Carotene in green feeds is a precursor of Vitamin A.
A feed low in protein will cause poor feathering, feather plucking and cannabilism. Eggs have low hatchability and growth is retarded. A shortage of the amino acid tryptophan is linked to nicotinic acid deficit causing leg weakness. If protein levels are increased, birds will recover
With Vitamin D these are essential in bone formation. If any one of the three is deficient symptoms will arise, and it is often difficult to find out which of the three is deficient. Vitamin D is obtained from sunlight, so unless birds are housed with no access to sunlight at all, it is unlikely to be Vit D. In the tropics, phosphorus is often low in grasses and crops but this does not normally affect poultry. Calcium is the most likely of the three to be deficient. When Ca and Phos levels are low, the bird will draw on it’s own body reserves to supply the shortfall. As a result, by the time the problem is noticed, it may be too late to rectify it.
Deficiency symptoms include bone abnormalities, low feed conversion ratios, impaired fertility and drop or cessation of egg production.
The requirements of various livestock for Calcium and Phosporus are shown in the table below.
|CALCIUM %||PHOSPHORUS %|
As can be seen, the requirements in the laying hen, particularly for calcium are very high. The average egg contains 2g of calcium, mainly in the shell, but only 0.1g of phosphorus. If calcium is deficient in the feed, or if the Ca:Phos ratios are inbalanced, the hen will draw on her body reserves for a few days. Once these are depleted, egg laying will drop dramatically or cease. If the hen has not used up too many of her own body reserves, feeding Ca:Phos as a supplement will result in increased lay and weight gains.
Although not often seen, iron deficiency in laying hens is theoretically possible, as an egg requires 1mg iron. Commercial feeds will have an adequate iron supply and free range birds never suffer from iron deficiency as they get enough from soil and green feed.
Birds have a higher requirement for manganese than mammals. Most grains used in poultry feeds (maize, sorghum, millet) are low in manganese so it has to be added as a supplement. Excess calcium or phosphorus limits the uptake of manganese by the bird.
The most indicative symptom of manganese deficiency involves the long bones and tendons of the legs. The long bones twist and shorten and there may be arthritis of the joints, especially the hock joint. The Achilles tendon detaches from the joint and slips sideways, a condition known as perosis or slipped tendon. The bird is immobilized and unable to feed.
Perosis due to manganese deficiency.
In adults, egg production drops and eggs may be infertile and thin shelled. There is a high incidence of bone deformity in hatched chicks.
Control and prevention involves the feeding of manganese as a supplement, especially if Ca:P is in excess. Manganese can be fed in the form of oxide, carbonate, sulphate or chloride at a rate of 70 ppm (21 g per 100kg feed)
Sodium chloride (Salt)
Sodium is required at 0.1% of daily intake. The body is very efficient at conserving sodium, but when levels are very low symptoms of deficiency will show. These are inappetence, weight loss, increase in water consumption, drop in egg production and cannabilism.
Birds recover quickly when salt is added to the diet.
Salt toxicity (excess) is rare in poultry, as they can tolerate high levels – up to 1.5% of intake.
Zinc deficiencies are rare and usually found when feeds contain high levels of soya, groundnut meal and cottonseed. The oilseeds contain high levels of phytic acid, which binds with zinc, making it unavailable to the bird.
Symptoms of deficiency are retarded growth, anoerexia and lesions of skin and feathers. There may be a severe dermatitis of the feet, poor feathering, abnormal respiration and shortened, thickened long bones. Zinc deficiency should be suspected when birds are fed on plant sources high in phytic acid, calcium intake is high and skin lesions develop. Zinc can be fed as a supplement at a rate of 50 ppm.
Selenium and Vit E
The relationship between Selenium and Vit E is not fully understood, but it appears that in the case of a deficiency of one of these micronutrients, feeding of the other will effect a cure.
Vitamin E deficiency causes exudative diathesis in adults. There is a massive oedema on the breast, wing and neck. Subcutaneous haemorrhages makes the skin appear bruised with a blue/green colour.
If chicks are affected in the first weeks of life by Vit E deficiency they develop encephalomalacia, or crazy chick disease. This is a nervous condition, apparently caused by haemorrhages in the brain. The chick will show loss of co-ordination, muscle tremors, torticollis (twisting of the neck) followed by renal failure and death.
Supplementary feeding of selenium (at 0.2-1 ppm) or Vit E (at 40 ppm) will prevent these disorders.
Selenium toxicity is rare. Chicks from hens having excess selenium show impaired development and may hatch eyeless, or with the upper beak missing. Hatchibility of eggs is greatly reduced.
Vitamin A (precursor carotene)
Carotene is found in green feeds and is necessary for the formation of Vitamin A in the body. Symptoms of deficiency include severe respiratory symptoms, coughing, pneumonia and infertility. Symptoms can be reversed by the supplemental feeding of Vit A or by feeding green feeds.
Vitamin B5 Niacin or Nicotinic acid
Maize is a poor source of Vit B5 so deficiencies may arise where maize is the main feed source. Symptoms are dermatitis, inflammation of the tongue and perosis due to severe bowing of the legs.
Riboflavine (Vit B2)
Deficiency results in slow-growing weak chicks, diarrhea and in severe cases paralysis and death. In chronic cases the toes curl up giving the claw a fist-like appearance.
Treatment is 100micrograms daily of riboflavine.
Pantothenic acid (Vit B3)
Maize is a poor source of Vit B3. Symptoms of deficiency are emaciation, dermatitis, crusts form at the angle of the beak, on the eyelids and feet.
Deficiency is rare as choline is found in most feeds. Symptoms are poor growth and slipped tendons (perosis)
As biotin is found in commercial poultry feeds, deficiency symptoms are rare. Affected birds have a dermatitis around the eyes.