Eggs are remarkable objects, from a good source of food right through to an incubation chamber. The eggshell and membrane hold the content of the egg, protect the egg from damage, and helps keep out bacteria. Keeping out bacteria is very important for our health and the health of any developing chicks.
It takes approximately 20 hours for a shell to form around the membranes. It is made up of a protein scaffold mixed with calcium carbonate crystals making up approximately 96% of the shell. The shell is deposited onto the membranes (along with pigment) in a region of the oviduct called the eggshell gland. The cells lining this gland are very similar to the cells lining the trachea (windpipe) and the kidney. This means that respiratory diseases such as Infectious Bronchitis, which attack the respiratory tract, can cause damage to the eggshell gland in the oviduct resulting in poor shell quality and lack of pigment i.e. a hen that normally lays brown eggs will lay pale/white shelled eggs.
CAUSES OF POOR/PALE EGG SHELLS
There are a number of causes of pale/poorly shelled eggs:
- Respiratory Diseases(IB, Newcastle Disease, Avian RhinoTracheitits virus/ART,Mycoplasma) can damage the egg shell gland causing poor shell quality. This is the most common cause of pale eggs and poor egg shells. If your chickens have abnormal shells then look closely for signs of Respiratory Disease. Most of these diseases are viral and antibiotics may have a limited effect on the problem. The birds may recover but a full return to their former glory cannot be guaranteed. If you want to determine which disease has cuased the problem then a blood test can be carried out. If you have a large flock you may wish to vaccinate.
- Bright sunlight in the summer can cause pale shelled eggs, however the exact reason for this phenomenon is still widely unknown. Keeping birds enclosed for several days can reverse this.
- Laying cycles – chickens coming into or out of lay will take a few days before their oviducts start to function properly causing poor quality abnormal shells. This can lead to thin shelled eggs. Furthermore, as the bird goes through her cycle, her oviduct loses its tone leading to oddly shaped eggs.
- Calcium or vitamin D3 deficiency can cause poor shell quality but this is rare. If the birds are on a good diet with some crushed oyster shell they should not have diet related egg shell problems. However, if you suspect that this is the problem then you can supplement the birds with vitamin D3.
- Stress can cause abnormal egg shells. If the bird is stressed (e.g. due to a predator attack), then the egg’s passage through the oviduct can be halted and extra shell can be added sometimes causing a ridged waist.
- Genetics – bear in mind that genetics can give a variety of shell colours from green shelled Legbar eggs to brown speckled Maran eggs to white shelled Leghorn eggs.
How to Improve Shell Quality
- Vitamnin C (Ascorbic Acid):Ascorbic acid is essential for synthesis of organic matrix (tropocollagen) of eggshell. Ascorbic acid alleviates the ill affects of heat stress by reducing the plasma cortisone level in the bird. Ascorbic acxid is a factor in the absorption of Vitamin D to the active hormonal metabolite ‘Calcitriol’ (OH)2D3), which stimulates intestinal absorption of calcium and thus elevates plasma calscium to a level that supports normal mineralisation of bones.
A dietary level of 250 mg ascorbic acid/kg diet of moulted hen improves the egg production and eggshell quality by enhancing intestinal calcium absorption or by resorption of bone Ca mediated through 1,25 (OH)2D3) production.
- Sodium bicarbonate (NaHCO3):Hens aged 30 weeks fed with 1% dietary NaHCO3and housed at 32ºC either in conventional or intermittent lighting programme had improved eggshell breaking strength. The improvement in eggshell quality was more in the group with intermittent lighting programme. Supplementation of NaHCO3 to laying hens at high temperatures is a means of improving eggshell quality as hens consume the additional bicarbonate during the period of active shell formation.
The addition of sodium bicarbonate or purified sodium sesquicarbonate, has shown to elevate the dietary electrolyte balance, improved acid-base balance and has a positive effect on eggshell quality.
- Aluminosilicates:Results indicate as much as 40% improvement in egg specific gravity and 2.2% improvement in feed conversion by the addition of 0.75% sodium aluminosilicate to layer diets. Shell quality increased in summer but not in winter. However, care must be undertaken while selecting composition and ion exchange capacity of silicates.
- Minerals:Zinc, Manganese and copper are compounds involved in the metabolic process of eggshell formation. These trace minerals work as co-factors of enzymes involved with shell matrix formation. Carbonic anhydrase, which is zinc dependant, stimulates calcium carbonate deposition for eggshell formation. Polymerase enzyme, which is dependent on manganese, forms the shell glycoprotein matrix or foundation.
Supplementing the diet with highly bioavailable minerals like mineral-amino acid complexes increases the eggshell weight and eggshell thickness. Copper affects the synthesis of shell membrane by activity of copper containing enzyme lysyl oxidase.
Dietary supplementation of zinc methionine improved the shell breaking strength. There was no improvement in shell quality where zinc sulphate was supplemented to approximate zinc concentration of zinc methionine.
- Calcium:Provide extra calcium to the older hens @1g/bird in the form of oyster shell over and above normal requirement in summer months. Maintain the desired particle size of calcium source at the time of shell formation. The minimum size of calcium source to improve gizzard retention is about 1 mm. Solubility and absorption of calcium source must be major criteria. Magnesium content of calcium source must be as low as possible. Organic calcium is also a good option.
- Chemicals:Injection of Indomethacin 4hr or 16hr post-entrance of egg into uterus delays oviposition and prevents premature expulsion of some soft shelled and shell less eggs. Chemotherapeutic agents like salicylic acid, aspirin reduce body temperature of laying hens during heat stress thereby alleviates its ill effects.
- Management:Reducing egg breakage at farms requires constant attention to management details and proper equipment maintenance. Some methods to reduce the percentage of broken eggs are:
- Provide cushioning of some type at the front of egg collection area of the cages. This will soften the impact of eggs rolling on to the collection wires and reduce the incidences of hairline cracks. Be sure that cushioning is positioned correctly to receive the eggs from the cages.
- Collect the eggs at least twice a day and more often if possible. Eggs rolling down the cage floor have an increased chance of being broken if there are several eggs already in the collection area.
- Maintain egg collection wires/trays in good condition. Examine them regularly for sharp edges, any foreign objects and for excessive wear and tear of the wire mesh/trays.
- Ensure that eggs do not pile up; dead birds protruding from the cage often block the egg flow to the collection area and causes spilling of the egg on the floor.
- Routinely check the quality and condition of the egg trays in which the eggs are collected from the cages.
- Train egg collection workers for carefully picking the eggs from the cage area and gently placing them in the collection trays without slowing down the collection process.
- Be sure that ventilation is well maintained and fans, if any are working properly during hot weathers. Try to provide constant ambient temperature as far as possible.
- Reduce sound, activity and movement of workers inside the layer houses as much as possible to reduce disturbances to the birds.
- Procure good quality feed ingredients devoid of contaminants, adulterants and mycotoxins and provide wholesome water at all times to the birds.
- Reduce flies, and rats causing annoyance to the birds.
- Check size, specific gravity, shell thickness routinely and if any change is observed, try to correct it by various means.
Though precise statistics are not available, the economic loss due to poor eggshell quality is estimated to be 2 billion dollars being at very conservative (assuming 150 million commercial layers and each bird losing @ 10 dollars/bird/ year due to cracked eggs). The above amount excludes the hatching eggs by breeding birds. These eggs have already been paid for the cost of production, so any successful effort to market a higher percentage means more net returns for the egg producer. The future of egg industry will go together with producer to innovate and supply quality eggs at reasonable cost.
Maintaining eggshell quality is a complex activity. it is impossible, even with current knowledge, to correct all eggshell quality problems. We can, however, make significant reductions in the number of eggs lost due to poor shell quality. This can be accomplished if one realises that no single factor is usually responsible for egg breakage. Many factors are known to be related with eggshell quality including, flock health problems, management practices, environmental conditions, breeding and adequacy of nutrition.
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