First quality eggs must have first quality shells. First the egg must have a strong shell to withstand transportation and packing. Second, a clean shell. Thirdly, and perhaps most important in the UK, a uniform brown colour.
The third of these is often the hardest to achieve and pale shells can be a particular frustration to producers.
The eggshell – what is it?
From the hen’s point of view, the purpose of the egg shell is to serve as a protective covering within which the embryo can develop to a chick. Obviously, in the modern laying flock, table eggs are not fertile but the egg shell is still of considerable importance to the customer and hence producer. The egg shell is mainly formed from calcium carbonate but also contains several trace elements including phosphorous, potassium, magnesium, sodium, zinc, manganese, iron, copper, boron and aluminium. All these nutrients must be supplied by the diet for optimum shell production.
The shell is formed in the oviduct. The albumen or egg white is formed mainly in the magnum. Formation of healthy albumen is vital for good shell quality as the albumen must be sufficiently turgid to provide support for the shell and shell membranes which will be deposited on it. If the albumen is watery, then it is impossible for shell deposition to proceed in the normal way.
In the isthmus, the paired shell membranes are laid down on the albumen. The egg then passes into the tubular shell gland where calcium salts are deposited on the shell membrane fibres. The egg doesn’t spend long in this region of the oviduct but this stage is vital for good shell strength and formation as it is laying the ’foundations’ for the main part of the shell deposition.
In the shell gland pouch, the main bulk of the egg shell is laid down. The shell is made up of 95% calcium carbonate and 5% organic material. Pigment is added to the shell quite late in the shell formation process hence problems with poor pigmentation if, for any reason, the egg is laid prematurely. The final process in shell formation is the deposition of the cuticle and it is known that eggs with poor shell pigmentation may lack some or all of the cuticle layer.
The pigment colouring brown egg shells is protoporphyrin. White shelled eggs also contain this pigment but the level present is far lower.
Loss of shell colour- why?
Nutrition: Deficiency in any of the main nutrients including protein, minerals and trace elements required for healthy egg production can influence shell colour and formation. The trace elements zinc, iron, copper and manganese are all thought to be important in transport of pigment into the shell. It has been suggested that magnesium supplementation of a layer diet can improve shell colour.
Viral infections: There are numerous viral infections notably Infectious bronchitis, Infectious bronchitis variants, Newcastle disease, Egg Drop Syndrome and Avian pneumovirus (TRT) which can cause damage to the oviduct, resulting in loss of shell colour and/or misshapen eggs. The effect on shell colour may persist for some weeks, particularly following Avian pneumovirus challenge. The problems due to viral challenge can be minimised by using a comprehensive vaccination programme and by regular serological monitoring of your flocks to plan a rearing vaccination programme for future flocks based on knowledge of challenges on your farm.
Parasitic problems: Heavy infestation with roundworms or capillaria worms can adversely effect egg quality and may result in pale shells and poor internal egg quality, particularly pale yolks. This effect is most likely to be due to damage to the intestine resulting from the parasitic burden which will reduce absorption of nutrients required for optimum egg production. In heavy parasitic infestations, there is often associated low grade bacterial enteritis which can also interfere with uptake of nutrients. Regular worming of laying flocks should reduce the risk of parasitic problems. Red mite, when present as a very heavy infestation, may also contribute to shell quality and internal egg quality problems.
Drugs: The coccidiostat drug, Nicarbazin, if present in layer feed can interfere with pigmentation.
Age: An older flock will often produce paler eggs. Treatment with specific vitamin mineral supplements to help shell quality may be beneficial.
Stress: Anything which ’stresses’ the hen can interfere with shell production. Depending on the problem, the egg may be retained in the oviduct for longer than usual and extra calcium is laid down resulting in ’splashing’ seen on some brown eggs. If the opposite happens and the egg is laid prematurely, then pigment deposition will be reduced resulting in a pale shell. ’Stresses’ can be physical disturbance to the birds, eg hot air balloons, nutritional stresses or environmental. It is sometimes very difficult to determine what a particular stress factor may have been. Perhaps the answer is to have more ’laid back’ chickens!
Weather: Over the last few years there have been increasing numbers of reports of pale shelled eggs in free range flocks in sunny weather. Anecdotally, this seems to be worse in flocks with poor feather cover. This problem is apparently triggered by sunlight and resolves if birds are housed again.
To date, no definite explanation has been found for this effect. Suggestions include interference with synthesis of the shell colour pigment, shell pigment synthesis and egg shell formation being out of sync or possibly a link with nutrition if there is a variation in nutrient intake when birds are spending more time on the range. It is known that high environmental temperatures can cause a decrease in shell thickness and perhaps a reduction in pigment formation.
This is a most frustrating problem and one into which more research is required as a matter of urgency.
In summary, we do not have all the answers to the pale shell problem, particularly the sunlight related effect. We would welcome any thoughts from readers as to their theories on this interesting but infuriating phenomenon.
