Nutrition plays a major role in the performance of layer birds. Feed management is the most important practice to achieve egg production at the right time, maximum peak production, long standing peak production, standard egg size, good cull bird weight and reduced feed cost per egg. Body weight should be taken every week from 1st week to 18th week of age, the birds with less body weight should be separated and special care must be taken to those birds to get uniformity in flock. The birds fed with standard feed prepared as per nutrient specifications will attain recommended body weight. The nutritional requirements of birds will vary depending on the breed, age and climatic conditions. So, feed formulation should be prepared as per the nutritional requirement of birds. In summer, the feed intake is less and the feed formulation will be revised as per the feed consumption.
Carbohydrates, proteins, fats, vitamins, minerals and water are main nutrients in poultry layers that are discussed as follows.
Cereal grains such as maize, bajra, broken rice, rice polish, jowar, ragi, de-oiled rice bran (DORB) and wheat bran, etc., are some of the carbohydrate sources used in layer diet. Most of the carbohydrates of cereal grains occur as starch, which is readily digested by poultry. Other carbohydrates occur in varying concentrations in cereal grains and protein supplements. These carbohydrates include polysaccharides such as cellulose, hemicellulose, pentosans and oligosaccharides such as stachyose and raffinose, all of which are poorly digested by poultry. Thus, these dietary carbohydrates often contribute little to meet the energy requirement of poultry and some adversely affect the digestive processes of poultry when present in sufficient dietary concentrations.
The vegetable protein sources are soya bean meal, sun flower cake, rapeseed meal, cotton seed cake, ground nut cake, guar meal, til cake, and distillers dried grains with solubles (DDGS), etc. Animal protein sources are fish meal, meat and bone meal, blood meal and feather meal etc. Proteins are polymers that are composed of alpha amino acids, which are linked together by peptide bonds. Proteins are broken down and hydrolyzed in the digestive system into amino acids. Then, after absorption, the amino acids will be assembled and metabolized to form proteins that are used in the building of different body tissues. They also serve vital metabolic roles as blood plasma proteins, enzymes, hormones and antibodies, each of which has a specific role in the body. The concepts of digestible amino acids, ideal amino acid ratios, use of synthetic amino acids and feed consumption-based formulations must be considered to get excellent result in layer flocks and saving in feed cost.
“Fat” or “oil” is another source of energy. Besides supplying energy, the addition of fat to animal diet improves the absorption of fat-soluble vitamins, decreases pulverulence, increases diet palatability and the efficiency of utilization of the consumed energy. Furthermore, it reduces the rate of food passage through gastrointestinal tract, which allows a better absorption of all nutrients present in the diet. The digestion of fat produces less body heat (fat has a relatively low heat increment), which is useful during periods of heat stress. Vegetable oils such as soya oil, rice bran oil and animal fat such as tallow are used as the energy sources.The presence of food in the duodenum stimulates the secretion of cholecystokinin, which induces the contraction of gall bladder and secretion of the pancreatic juice, making the chime. Colipase binds to the oil-water interface and produces the emulsion. Afterwards, triglycerides undergo hydrolysis under the action of the pancreatic lipase and micelles are formed by monoglycerides, diglycerides and free fatty acids. Micelles are absorbed through intestinal villi.
Vitamins are present in the feed raw materials such as corn and soy, but these are insufficient for the birds. Therefore, vitamins are supplemented as vitamin premixes in feed. Vitamins have been divided into two groups based on their solubility in fat solvent or in water. Thus, fat-soluble vitamins include vitamin A, D, E and K. While, vitamin B complex and vitamin C are classified as water soluble vitamins. Fat-soluble vitamins are found in feedstuffs in association with lipids. The fat-soluble vitamins are absorbed along with dietary fats, apparently by mechanisms like those involved in fat absorption. Water soluble vitamins are not associated with fats. Commonly used vitamins in layers are fat-soluble vitamins such as Vitamin A, D3, E and K. Water soluble vitamins are Vitamin B1, B2, niacin, pantothenic acid, pyridoxine (B6), biotin, folic acid, Vitamin B12, choline, Vitamin C, carnitine and inositol. Classical added choline levels used for layer diet are usually around 250ppm, but for an efficient action on liver, 500 to 1000 ppm of added choline is recommended. Vitamin B12, folic acid and vitamin E improve the liver condition.
DEFICIENCY OF VITAMINS:
The deficiency of vitamins and its affects were described by Simon as follows: Vitamin-A deficiency:
Vitamin A deficiency in chicks leads to poor growth, feathering and in advanced cases ataxia (inability to stand), xerophthalmia (dry eye) and chronic purulent conjunctivitis. Deficiency of vitamin A in layers causes deterioration in internal egg quality and a high prevalence of blood spots.
Vitamin-D3 deficiency: Vitamin D3 deficiency will lead to rickets in immature flocks, swelling of joints, depressed growth and poor feathering. In mature laying birds, deficiency of Vitamin D3 results in osteomalacia characterized by decreased skeletal density, production drop and reduced egg shell quality.
Vitamin-E deficiency: Vitamin E deficiency in chicks leads to encephalomalacia, transudative diathesis and muscular dystrophy.
Vitamin-K deficiency: Vitamin K deficiency leads to subcutaneous hemorrhages that are noted on the head and beneath the wings.
Vitamin-B1 (Thiamine) deficiency: Vitamin B1 deficiency in 10 to 20 days old chicks comprises incoordination and an abnormal retraction of head (star gazing). Vitamin-B2 (Riboflavin) deficiency:
Vitamin B2 deficiency leads to curled toe paralysis, low growth rate, poor feathering and low egg production. Biotin deficiency: Affected flock demonstrates poor growth, feathering and elevated mortality. The principle sign comprises dermatitis of the feet and skin, adjacent to the angle of the beak.
Minerals are classified into 2 types:
Macro Minerals: Macro minerals are required in large amount in the diet. Calcium, chlorine, magnesium, phosphorus, potassium, sodium and sulfur are macro minerals.
Micro (or) Trace Minerals: Micro minerals are needed in very small amount in the diet. Manganese, zinc, iron, copper, iodine, selenium, cobalt and chromium are micro minerals. The mineral content in the soil is becoming deficient because of continuous usage of land and intensive cropping. Trace mineral contribution from raw materials are not sufficient to fulfill the breed requirement because of the increased production performance of birds. So, trace minerals premix is supplemented for enhanced performance of birds.
DEFICIENCY OF MINERALS
Steeven Leeson detailed about the mineral deficiency in poultry as follows: Calcium and phosphorus imbalance: Deficiency of either calcium or phosphorus in the diet of young growing birds results in an abnormal bone development and lack of normal skeletal calcification. Rickets is seen mainly in growing birds, whereas, calcium deficiency in laying hen’s resulting in a reduced egg shell quality and subsequently osteoporosis. This depletion of bone structure causes a disorder commonly referred to as “Cage Layer Fatigue”. If calcium level is low in feed, the feed consumption will be of more helpin proper egg shell formation. Generally, 65% marble grit of 2-4mm size and 35% lime powder is used in laying phase feed.
Magnesium deficiency: Natural feed ingredients are rich in magnesium; thus, deficiency is rare. Magnesium deficiency in laying hen’s results in a rapid decline in egg production. Potassium deficiency: Affects osmoregulation. Sodium deficiency: Deficiency of sodium leads to lowering of osmotic pressure and a change in the acid-base balance in the body. It also leads to cannibalism, reduced egg production and poor growth in layers. Chloride deficiency: Deficiency of chloride causes ataxia with classic signs of nervousness and often induced by sudden noise or fright. Manganese deficiency: In layers, deficiency of manganese causes perosis, reduced egg production and egg shell thinning. Zinc deficiency: In young chicks, signs of zinc deficiency include retarded growth, shortening and thickening of leg bones, enlargement of hock joint, scaling of the skin especially on the feet, poor feathering, loss of appetite and in severe cases mortality. Whereas, in layers it results in lowered egg production. Iron deficiency: Deficiency of iron causes severe anemia. Copper deficiency: Deficiency of copper leads to ataxia and spastic paralysis. Iodine deficiency: Iodine deficiency results in goiter. Selenium deficiency: Deficiency of selenium in layers leads to lowered egg production and adverse effects in feed conversion.
Water is one of the most important nutrient in a laying flock. Hence, shortage of water for few hours results in reduced egg production. Water softens feed and carries it through the digestive tract. As a component of blood (90% of blood content), water carries nutrients from the digestive tract to cells and carries away waste products. Water also helps in cooling the bird through evaporation. Birds do not have sweat glands, so their heat loss occurs in the air sacs and lungs through rapid respiration. There is no precise quantity requirement for water because there are several factors that affect the amount of water a bird needs: age, body condition, diet, temperature, water quality and humidity.
While preparing the feed formulation, proper raw materials, cost and availability of raw materials must be considered. Feed formulation should be based on the age of the birds, nutritional requirement of the breed and feed intake of the birds. The nutrients in the feed raw materials should be utilized efficiently through proper digestion and absorption of nutrients by using emulsifier and enzymes.
by Dr. S R Prabakar, Kemin Industries South Asia