Shell quality is mostly influenced prior to the egg being laid and the thickness is directly related to the amount of time the egg has spent in the shell gland.
The time of day in which that egg has been laid also determines the thickness; generally the earlier in the day, the thicker the shell. It is obviously strongly influenced by the rate of calcium deposition also.
Darker shelled eggs tend to have better shell quality than lighter shelled eggs. This is likely to be a result of the birds’ health being compromised and so the best nutrients in the feed are keeping the bird alive, rather than a healthy bird utilising its feed to the full potential. Pale eggs can also be caused due to hens being exposed to too much sunlight. Unfortunately, why too much sun affects the pigmentation on the surface of the egg is unknown.
Quite an obvious cause of compromised shell quality is the presence of disease. IB will generally cause rough shelled eggs, discolouration and wrinkling of the shell. IB affects every portion of the reproductive tract and will also affect the egg quality inside (watery whites), as well as out. IB causes the shell gland cells to degenerate and distort which causes the misshapen eggs. Pale eggs will usually be seen two to five days after exposure to IB, as the virus will affect the uniformity of pigmentation.
Management is a key factor influencing shell quality. The shell constitutes for 11% of an egg. Generally, the rule of thumb is ‘bigger the egg, thinner the shell’. As a result, it is very important to pay close attention to feeding and lighting programmes. Whilst we are still seeing a high demand for large eggs, it is imperative that we manage that egg size and do not let it run away with us. The longer it takes to extend the daylight hours from 10-16, the more sexually mature that hen will be when she comes into lay, and therefore the larger the egg she will lay. Following this, it is then important to weigh eggs on a regular basis and change diets accordingly. This is something that CMC are very happy to assist each producer with.
Shell thickness and strength will deteriorate with age. The hen will lose some of her ability to mobilise calcium from the bone and therefore less able to produce calcium carbonate needed for shell formation. This mobilisation of calcium can decrease to less than 50% after 40 weeks of age.
If the birds come under stress, this causes secretion of acidic cells which therefore damages the cells lining the oviduct and uterus. In cases of extreme stress, calcium deposits will be seen on the surface of an egg along with misshapen eggs.
As a result, there are many factors which can affect shell quality. It is a critical part of producing eggs as it can obviously have some strong financial implications if it is not kept on top of.