MANUPULATION OF EGG CONTENT (QUALITY & NUTRITION) IN COMMERCIAL LAYER POULTRY FARM
Nutrition and egg quality
Egg content can be manipulated by nutrition. The major changes that can be brought through nutritional manipulation are egg number, egg size, egg shell quality, yolk pigmentation and enrichment of eggs with fatty acids; vitamins and minerals.
Egg size
Egg size is expressed as weight of the egg. The factors that affect egg size include protein and amino acids profile, balancing of amino acids, and levels of dietary minerals, vitamins and linoleic acid, and strain and age of the birds. Increasing protein level up to 20%with balanced amino acid level in diet increases egg size progressively, and about 1% larger egg can be achieved for every 1% increased protein content up to
20% CP level. Deficiency of protein decreases albumin content of egg and egg size. Therefore, selection of protein level in diet to achieve optimum egg size is a point of economic consideration depending upon market premium for larger eggs. Birds respond to increased methionine concentration in diet (up to 0.40%) by increasing egg size. Low level of vitamin D3and high level of calcium may result in reduced egg size. Linoleic acid influences egg size but not number of eggs produced. The requirement of linoleic acid is 0.5 to 1.5%. Birds provided maize in diet (30% or more) do not require attention for linoleic acid contents in diet, as its content is sufficient in maize (2.20% linoleic acid) and also in sorghum (0.8 to 1.1%) or pearl millet (0.84%) based diet. However, wheat (0.5 to 0.6%) based diets require special attention for linoleic acid contents. Certain unidentified factors normally present in diet also improve egg size. Egg size is low initially at the points of lay, increased gradually to second phase of egg production (about 50-55weeks) and then reduced with age. Tranquilizers have been reported to increase egg size.
Egg shell quality
The nutritional factors affecting egg shell quality include certain minerals like calcium, phosphorus, magnesium, chlorine and zinc, and vitamin D3. The different calcium sources and vitamin D3have beneficial effect on egg shell quality. Deficiency of vitamin D3and calcium causes production of thin-shelled eggs. Phytase may help to maintain egg shell quality for a lower dietary phosphorus level. Manganese deficiency cause egg shell thinning. The addition of much common salt (beyond 0.3%) is associated with thinning of shell wall and decreased broken strength of egg shell. Chloride of common salt decreases bicarbonate level in blood. The maximum level of chlorine thus be 0.14% in diet. A positive influence of manganese chelates on egg shell quality has been observed. Though the deficiency of magnesium is not common, but thin and brittle shell may occur due to deficiency of magnesium. The problems of shell quality have been the major concern especially during summer. In older birds too the egg shell becomes thinner. Certain sulphonamides cause thin shell. The diseases like infectious bronchitis and Ranikhet disease may lead to poor shell quality.
Internal egg quality
The concentration (% or g/100g of shell less egg material) of protein and major amino acids are protein, 12, lysine 0.82, methionine 0.40, cystine 0.26, arginine 0.80, iosleucine 0.84, leucine 1.02, •threonine 0.66, tryptophan 0.25. Accordingly, a 58 g of egg, provides 7 g of protein, 5 g of fat, 0.45g of lysine, 0.36 g of methionine + cystine, 0.44 g of arginine, 0.36g of penylalanine, 0.13gof tryptophan. The amino acids, vitamins and minerals content of the eggs can be improved by manipulating their dietary concentration. The iodine concentration can be increased by adding its suitable supplement (potassium iodide or iodate). It is fact that the vitamin content of eggs depends upon the dietary vitamin level, and poultry diet supplementation has been considered as a means of egg, vitamin enrichment for human nutrition. However, vitamin incorporation in eggs has evolved for the benefit of poultry rather than human. Riboflavin is increased easily in egg if fed through l iet in additional quantity. The level of vitamin E in egg increases as its concentration in diet is increased. However, the efficiency of vitamin E and beta-carotene incorporation is low (15% for vitamin E and 0.3%for beta-carotene), but it is higher for vitamin A. The feed ingredients especially agro-industrial byproducts or non-conventional feed sources have no adverse effects on egg quality. However, feeding of cottonseed meal, containing gossypol, to laying hens may cause in production of olive-green to dark brown egg yolks. Reports indicating the response of some breeds to high dietary fat levels, which revealed strain related differences for egg mass, Haugh unit, percent egg yolk, albumen and shell. Another important concern is yolk pigmentation i. e. to obtain a safe and constant yellow colour of the yolk. The presence of yellow xanthophylls in the diet is essential to avoid the risk of discoloration. The egg yolk colour can be maintained either by providing at least 30% maize (yellow) in diets, adding 3 to 5% of good quality leaf meal (Lucerne meal, spinach meal, Leucaena leucocephala] subabool leaf meal, berseem leaf meal), marigold powder, dried faecal pellets (5%) of goat browsing on green leaves or by supplementing xanthophylls (22 mg/kg diet). Some synthetic pigments are substitute of xanthophylls. But it is always better to have natural pigments than the’ synthetic pigments.
Designer eggs
There are growing public concern over consumption of eggs being high in cholesterol (200-300mg) and poultry meat with more of saturated fatty acids and cholesterol. It may be of economical advantage for the producer to market eggs with low cholesterol and meat with low fat. Numerous, including nutritional factors have been demonstrated to alter cholesterol deposition in egg. Cholesterol content of egg yolk may be altered by about 25% through manipulation of dietary fat/ energy and cholesterol. Dietary fiber and administration of certain drugs also reduces yolk cholesterol concentrations but only marginally. However, it will be commercially viable only when egg cholesterol is reduced (50%) to a level of 125 to 150 mg/ egg. Another approach has been to let the hens lay eggs enriched with omega-3 fatty acids (n-3 polyunsaturated fatty acids, docosohexaenoic acid and icosapentaenoic acid), due to the beneficial effect of the polyunsaturated fatty acids (n-3) on human health. Higher intake of polyunsaturated fatty acids (PUFA) decreases the risk of heart diseases and strokes, and also exerts immunological and neurological effects. These eggs should also have lower omega6/omega-3 ratio than the normal eggs, which is beneficial for consumption. The dietary PUFA are readily incorporated into eggs. The main sources of PUFA are fish oil, linseed, millets and sea algae. The sea algae are the best sources for producing omega-3 fatty acid enriched eggs. Moreover, their PUFA content is more stable and in more active form that in the plant oils. The cereals such as corn, barley and oats are also rich in linolenic acid. The combination of animal (fish oil) and vegetable oils viz. rapeseed, linseed oils is also effective. Egg enrichment in n-3 fatty acids results in higher rate of oxidation that could be controlled by the antioxidants such as alpha-tocopherol. Therefore, adequate amounts of alpha-tocopherol should also be supplied to obtain eggs with adequate antioxidant protection of PUFA that prevents the unwanted oxidation and the related health problems. The supplementation of diet with 200mg vitamin E per kg feed may reduce fatty acids (n-3) oxidation.