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This article was published in 1941
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
NUTRITION IN RELATION TO DISEASE IN POULTRY
L. HART. B.V.Sc., H.D.A.. Veterinary Research Station, Glenfield.
For normal health, growth and reproduction, poultry require a complexity of substances in their rations, including proteins, carbohydrates, fats, fibre, minerals, vitamins and water. These substances are necessary for other forms of animal life, but in view of specialised methods of production, deficiencies are more likely to occur in poultry.
Proteins are composed of amino acids, and in order to obtain a wide range of these it is necessary to supply protein in more than one form, and to include animal protein, such as meatmeal, fishmeal, milk products. Protein requirements vary with the class of bird, the optimum amounts being:
Birds 1-6 weeks, 17 per cent. protein.
Birds 7-12 weeks, to 15 per cent. protein.
Birds 13 weeks to maturity, 13 per cent. protein.
Laying hens, 16 per cent. protein.
These figures are for the complete ration, and where any system other than all-mash is followed, the amount of protein in the mash must be increased. Deficiency of protein results in poor growth and lower egg yield, and may precipitate an outbreak of cannibalism.
Fibre is necessary to provide bulk to ensure the normal functoning of the digestive system, but as in the fowl this is not designed for handling large amounts of fibre. Foodstuffs containing excessive amounts are unsuitable. Several workers have shown the value of fibre in preventing cannibalism, excellent results being obtained by the inclusion of oat-hulls to the level of 11 per cent. of fibre in the ration.
Salt is essential for growth and production. The addition of 1 per cent. of common salt to the ration will supply requirements, and where meatmeal or dried milk is included in the ration the addition of 0.5 per cent. probably will be ample. Deficiency of salt interferes with the utilisation of digested food and retention of calcium and results in poor growth, susceptibility to disease, retarded sexual maturity in young birds, while in laying hens there is decrease in body weight and in egg production. Large amounts of salt are toxic, but in chickens the mortality is not excessive until the salt level rises above 5 per cent. Birds dying from salt poisoning exhibit a large haemorrhage at the base of the heart, intense congestion of kidneys, slimy mucous membrane of proventriculus, and small intestine and occasionally intense enteritis. In chronic cases there is a straw-coloured gelatinous exudate beneath the skin in the region of the crop and frequently in other portions of the body.
Calcium and Phosphorus.—Calcium is required in large amounts for skeletal development (ossification) and egg production. An average egg including the shell contains 2 gm. of Ca. Phosphorus is intimately bound up with Ca in bone formation. The factors concerned in producing satisfactory growth and calcification of bone are the Ca : P ratio, the absolute amounts of Ca and P, and the level of vitamin D. Salt is necessary to ensure Ca retention. In young growing birds departure from the optimum in any of these factors will produce rickets. Rickets is usually due, however, to deficiency of vitamin D. Whilst the optimum Ca : P ratio is variable, being influenced by the supply of vitamin D and the level of Ca and P In the ration, the ratio should be about 2 : 1, and in growing mashes up to 2.0 per cent. Ca and up to 1.0 per cent. P should be present. Laying birds require additional amounts of Ca supplements, such as limestone or oyster shell, to provide material for shell formation, avoiding sources containing large amounts of magnesium, as this interferes with assimilation of Ca. Failing this, Ca is withdrawn from the skeleton, and as this process is prolonged a "rachitic" condition, in reality osteoporosis, develops.
Manganese is an essential "trace" element, a deficiency of which causes perosis or slipped tendon." An excess of P may also cause perosis, and excess bonemeal may bring it about. The condition occurs in birds from 3-8 weeks old and is characterised by slipping of the Achilles tendon from the groove at the point of the hock, which causes the leg to be twisted laterally. One or both legs may be affected, and once the condition develops it is not possible to effect a cure. Although chickens may be affected it is much more common in turkey chicks. In the latter, addition of manganese to the diet will not entirely prevent the condition, but recently choline has been found to prevent it. The presence of 50 p.p.m. of manganese in the ration is sufficient to prevent perosis in chickens, but high Ca P rations raise the manganese requirements (4 ozs. manganese sulphate per ton of feed is ample). Deficiency of Mn in the ration of the laying hen results in low egg production, and high mortality of embryos.
Magnesium disturbs the Ca and P metabolism, and materials such as dolomitic limestone, which contain appreciable amounts of Mg., are to be avoided as mineral supplements.
Fluorine.—Even small amounts exert a detrimental effect. The clotting time of the blood is decreased and small haemorrhages frequently appear in the duodenal loop (rock phosphate contains deleterious amounts).
Iodine is essential and in its absence goitre develops. Only small amounts are needed, and no cases have come to our notice in this country.
Vitamins.
Vitamin A is essential for life and is supplied to poultry mainly as greenfeed which contains carotene, a precursor of vitamin A. Deficiency causes definite symptoms and lesions and results in lowered resistance to respiratory diseases. Day-old chickens fed on a ration deficient in vitamin A grow at a fairly normal rate for 3-4 weeks. Then there is cessation of growth, staggering gait, drowsiness and ataxia, emaciation and weakness. Some birds develop xerophthalmia. In laying hens deficiency of vitamin A results in lowered egg production and the birds become dejected. Areas of diphtheresis develop in the mouth and "pustules" may be seen on the back of the pharynx. A nasal discharge may be present, the eyes become swollen and there is a profuse watery discharge. A white caseous exudate distends the conjunctival sacs. On post-mortem examination "pustules" are seen on the walls of the pharynx and often extending down the oesophagus. The larynx may be occluded with a caseous plug and a good deal of caseous exudate may be present in the trachea. The kidneys and ureters are distended with urates and the bursa of Fabricius is distended with caseous exudate.
The provision of adequate supplies of vitamin A brings about recovery in a remarkably short space of time, in all but the cases in extremis. Young chickens require 700 units vitamin A per pound of food consumed, whilst laying hens require 2500 units per pound of food. In the latter, provision of good quality greenfeed at the rate of 5-8 lb. per 100 birds per day will fulfil requirements. Where greenfeed is not available some supplement such as cold liver oil should be used. A good sample of cod liver oil contains 1000 units vitamin A per gm., and thus 1 per cent. added to the ration should be more than ample. If symptoms are present it is advisable to feed 2 per cent. for a week or two, and in advanced cases to dose the birds individually.
Such supplements should be mixed with the mash on the day of feeding, as vitamin A is rapidly destroyed by oxidation. Also the oil should be kept tightly stoppered.
Vitamin B—The factors of the B complex which are of main concern in poultry nutrition are thiamin (antineuritic), riboflavin (curled toe paralysis+), pantothenic acid (chick antidermatitis factor), and pyridoxine (growth). Under our conditions the two factors with which we are mainly concerned are riboflavin and the filtrate factor (pantothenic acid).
Riboflavine—Rich sources of this substance are yeast, liver meal, milk products, and greenfeed. Deficiency in breeding hens results in poor hatchability. Symptoms of deficiency are seen in young growing chickens and most cases develop between the 3rd-10th week. Onset is sudden, the birds have difficulty in using their legs, sink on to their hocks, and the toes twist inwards and curl up (flexion). In turkey poults the toes and shanks become swollen and oedematous, the skin cracks and fissures and "corn-like" swellings may appear on the plantar surface of the feet. On post-mortem examination there is marked enlargement and oedema of the sciatic nerves and yellowish colouration.
In early cases administration of riboflavin brings about recovery in 2-4 days.
Pantothenle acid.—Rich sources of this are yeast, liver meal, milk products and molasses, whilst grain and mill offals contain a fair amount. Deficiency results in dermatitis. As most substances rich in riboflavin are also rich in pantothenic acid, both substances are likely to be lacking in the event of a deficiency, and thus curled toe-paralysis and dermatitis will be present together.
Vitamin D is necessary for the proper assimilation and utilisation of Ca. Under natural conditions where birds are run in open yards with access to sunshine no supplement is required. When sunlight is not available, such as with chickens in battery brooders, some vitamin D supplement is necessary, and in its absence rickets develop. Chickens in the absence of sunlight require at least 20 units per 100 gm. feed. whilst breeding hens under similar conditions require 80 units per 100 gm. feed for maximum hatchability. A good sample of cod liver oil contains 100 units vitamin D per gm. and thus 1 per cent. added to chicken rations will be ample to ensure proper calcification of the bones provided there is sufficient Ca and P in the ration, the Ca : P ratio is right and there is not an excessive amount of magnesium present. Symptoms do not usually appear till thickens are two to three weeks old. There is retardation of growth and the gait becomes unsteady and proppy. The beak becomes soft and deformed, the costochondral junction become enlarged, and finally the chickens are unable to stand. On post-mortem examination the bones are found to be soft, the long bones bending instead of snapping between the fingers.
Except in the worse cases recovery takes place following exposure to sunlight or supply of vitamin D supplement.
Vitamin E (a-tocopherol) is present in wheat germ and under ordinary conditions there will be no deficiency. In the absence of vitamin E from the ration a condition known as encephalomalacia develops. Symptoms appear usually 3 to 5 weeks after hatching and consist of ataxia, coarse tremors, retraction or twisting of head, prostration, stupor and death. Lesions are confined to the brain and consist of oedema, necrosis and haemorrhages, and are usually macroscopic.