Analysis on the Requirement of Calcium and Phosphorus for Laying Chickens

2021-03-25 Back to List

The macro mineral elements contained in chicken body tissues and eggs are calcium, phosphorus, potassium, sodium, sulfur, magnesium and chlorine. Some of these elements are important chicken feed making raw materials that constitute chicken body tissues, such as calcium, phosphorus, sodium, potassium, and chlorine, together with phosphate and carbonate to maintain a stable internal environment, such as regulating the body's acid-base balance and the penetration of various parts of the body. Therefore, in order to maintain chicken body health, normal physiological functions, growth and development, meat production and egg production, various macro mineral elements must be supplied to chickens.

1.Calcium

Calcium is an important component of the bones and hard tissues of the chicken body. More than 90% of the total calcium contained in the chicken body is present in the bones. The calcium in defatted bone accounts for about 1/3, mainly composed of calcium phosphate, about 10% of calcium Contained in soft tissues, it plays an important role in maintaining the excitability of muscles and nerves and the normal coagulation process. The calcium requirement of laying hens is 4 to 5 times that of non-laying hens. 

The egg content contains a certain amount of calcium, and the main ingredient of the egg shell is calcium carbonate. An egg contains about 2.28 grams of calcium, and each egg needs to supply about 4 grams of calcium. Although the calcium stored in the marrow bones of laying hens can be supplied to form eggshells, its storage is only enough to form 6 eggs, and the amount of calcium lost from eggs by hens is very considerable, the total amount of calcium excreted throughout the laying season It can reach 500 grams, which is about 20 times the hen's reserve when she starts laying eggs.

Therefore, the laying hens must always be supplied with sufficient calcium from the feed. When there is a lack of calcium in the feed, the hen's egg production rate and egg hatching rate will be reduced, and the production of sand-skinned eggs, thin-shelled eggs, and soft-shelled eggs will increase significantly. According to reports, the minimum feed calcium concentration to ensure a good egg production rate is 2.25%. There are also reports that feed calcium content above 2.8% can meet the highest egg production rate, and high-quality eggshells can be obtained above 3%. 

The calcium in the feed is absorbed The rate is 50%~60%. It is generally believed that the daily intake of calcium for laying hens should not exceed 4.5 grams, and the appropriate calcium content of feed should be 3.5% to 4.0%, not more than 4%. Supplying 1/3~1/2 of the calcium requirement in granular calcium (limestone granules or shell gravel) can make the hens get a good supply of calcium within 24 hours a day, which is beneficial to improve the quality of eggshells.

Too much calcium in the feed is also disadvantageous. The digestive tract of 1 to 3 weeks old chicks is extremely sensitive to the calcium level of the feed, and the high calcium level raises the intestinal pH to 6.5 or even higher. At this time, manganese forms an insoluble complex and cannot be absorbed. Zinc also combines with phytic acid to form a complex that cannot be used by chickens, and the absorption of phosphorus is also blocked. After 21 days of age, young chicks can tolerate high calcium levels, but high calcium should not be used because high calcium will inhibit the development of glands or organs (mainly parathyroid glands) that control the calcium feedback mechanism. Controlling the feed calcium in the young period to a level that can only meet the needs, generally 0.8%~1.0% will allow these glands and organs to develop normally, so that the young chickens will grow into layers and enter the laying stage. Calcium needs to be mobilized from the bones. When the eggshell is formed, the body can be controlled by it.

Feeding high-calcium feed to growing chickens can cause kidney disease, visceral gout, fallopian tube stones, growth retardation, delayed sexual maturity, and increased mortality. The adverse consequences will continue until the laying period. According to reports, feeding excessive calcium to growing hens can cause "latent" kidney damage, which can develop into urolithiasis when the hens mature. Therefore, laying hen feed should not be given to young hens before 14 weeks of age. Too high levels of calcium in layer feed will reduce egg weight. For every 1% increase in feed calcium, egg weight will be reduced by 0.4 grams. The high concentration of calcium and phosphorus in the feed can significantly reduce the absorption rate of manganese and cause the poultry to develop tibial phrenia or tendinopathy. There have also been reports of excessively high calcium supply causing massive prolapse of laying hens.

2. Phosphorus

Phosphorus is a mineral element second only to calcium in the chicken body. It is the main raw material for chicken bones. About 80% of the total amount of phosphorus in the chicken body is present in the bones. The other phosphorus is contained in the soft tissues and constitutes some of the soft tissues. The components of the buffer system in substances and body fluids, and have an effect on the body's metabolism. Therefore, a certain amount of phosphorus must be contained in chicken feed. When the phosphorus in the feed is severely lacking or the availability of phosphorus is poor, it will quickly cause the chicken to lose appetite, become weak, and die within 10 to 12 days. 

Laying hens showed decreased egg production, reduced egg weight, reduced hatchability, and osteoporosis. The feed must contain sufficient phosphorus before giving birth, and reducing the effective phosphorus will increase the kidney damage caused by excessive calcium. Each laying hen needs 400 mg of available phosphorus per day, and the content of total phosphorus and available phosphorus in the feed is generally 0.5% to 0.6% and 0.4%. According to reports, when the feed contains 0.30%~0.35% available phosphorus and 3.5% calcium, calcium can produce the best effect in terms of egg production and eggshell strength.

3. Calcium to phosphorus ratio

Compared with calcium, the requirement of phosphorus is lower. The content of calcium and phosphorus in the feed should be appropriate, and the best ratio between the two should be maintained. Too much calcium affects the absorption of phosphorus, and too high phosphorus in turn affects the absorption of calcium. The ratio of calcium to total phosphorus in the feed for growing chickens ranges from 1.1 to 2.2:1, generally 1.4 to 1.5:1. The ratio of calcium to total phosphorus in the feed for laying hens should be between 5 to 6:1. 

The phosphorus required to form eggshells is much lower than calcium, so layer hens rarely suffer from phosphorus deficiency under normal feeding conditions. An egg shell contains only 20 milligrams of phosphorus, while the yolk contains 130-140 milligrams of phosphorus. The total phosphorus content of an egg is about 160 mg. For a hen that lays 300 eggs per year, the amount of phosphorus deposited in the egg is about 41 grams. When the ratio of calcium to available phosphorus in broiler brooding and finishing feed was 1.75-2.22 and 2.5-3.0, the incidence of abnormal legs was the lowest.

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