Skip to: main navigation | main content | sitemap | accessibility page



Call +44 (0)1392 872932

Understanding the Shell

Suzy Ackerley BVMedSci (Hons) BVM BVS (Hons) MRCVS

Poor shell quality can limit flock productivity and shorten a production cycle. From “hair-line” cracks to completely absent shells, without a fully intact structure, an egg cannot be sold for maximum worth. The diets of most commercial layers are supplemented with calcium at a rate of 3.8-4%. Vitamin D3 and phosphorus are important ingredients too. These are typically supplemented at a rate of 3000IU and 0.45-0.5% respectively. Vitamin D3 is especially important because it facilitates the uptake of calcium into the body.

Most flocks will receive something in the form of pro-active supplementation for shell support. Various in-feed formulations are available. Some producers opt for in-water preparations instead. Others only choose to support shell quality if or when there is an obvious abnormality. The physiology governing shell quality and formation is multi-factorial. For this reason, “treatment” or “supplementation” can be challenging and unrewarding.

Table 1 lists factors influencing shell quality. It is a very complex interaction of pathways. Shell largely consists of calcium carbonate and of the 25 hours taken to produce an egg, 20 of these are spent on building the shell. Up to half of the dietary calcium is used for shell production and this should provide most of what is required for this process. However, the bird can draw upon calcium stored in bone when necessary. This happens when intestinal calcium supplies are either sub-standard, or the absorption process is not working correctly.

Table 1: Factors influencing shell quality

Temperament (flightiness)

A good proportion of shell is formed during the night, and it is important that the bird has eaten enough to ensure enough food is available within the intestine at this point. However, it is important to remember that physical disturbances, such as heavy red mite infestation, can significantly interrupt rest periods and negatively impact upon shell quality.

Ideally, the bird works to balance calcium uptake from the intestine and bone, in a way that avoids bone depletion. Osteoporosis occurs if this process is imbalanced. This is difficult to reverse in a commercial setting. Shell quality support should be timed so that birds do not draw on skeletal calcium reserves more so than those in the intestine. By 40 weeks of age, most flocks should be receiving shell support product(s). This is often well before any changes in shell integrity and strength are detected, but as we have already discussed, shell formation is a multi-factorial process, and does not respond that quickly or efficiently to reactionary interventions.

Intestinal health has a significant impact on shell quality. Any flock suffering with loose droppings could be suffering a relative deficiency in the components required for good shell quality. Rapid gut passage of nutrients does not allow enough time for absorption across the intestinal wall into the bird’s bloodstream. Equally, an inflamed mucosa (lining of the intestine) will impede the absorption of necessary nutrients from the diet. Worm infestations further complicate the picture because of the low-grade inflammation they cause, but also because they can directly compete for essential nutrients, which are then unavailable for maintaining a healthy bird.

Once in the bloodstream, nutrients required for shell production are carried on proteins. These proteins are produced by the liver. The liver must be in good working order to make these. Managing shell quality can therefore be seen as part of the holistic management of the bird, as healthy intestinal and liver function is key not only to metabolism, but immunity too. We know immunity naturally wanes as the bird ages, and this is relevant to shell formation and structure because certain diseases such as Infectious Bronchitis (IB), Avian metapneumovirus (APV), Mycoplasmas (MG/MS) and Egg drop syndrome (EDS) are more likely to infect birds. All of these diseases directly affect egg production as well as shell quality, meaning that fewer, poorer quality eggs are laid. The effect of disease upon shell quality can be more profound in flocks that are not receiving support for shell quality.

Research has shown that supplementation with calcium and vitamin D3 can increase egg production, as well as improve food conversion, immune function, egg mass and shell quality. It is therefore worthwhile investing in the shell, for reasons other than maintaining good shell quality. A few factors must be considered when deciding on the type(s) of supplementation required, bearing in mind that each flock is different, and that is why relying on standard ration formulations alone can be a false economy.

In-water supplementation can quickly be administered and is useful at times when treatment for poor shell quality is required. Most applications are either continuous or are applied over several days each week. This can make water sanitisation and the co-addition of other products, such as wormer, particularly challenging. In-feed applications are more popular and can facilitate a more consistent delivery of product. Some products can slightly alter the taste of the ration; limestone and oyster are calcium-based, and some producers notice a brief change in feed consumption, due to a change in palatability when transitioning onto these products. Limestone is particularly economical, but bear in mind quality can vary, especially when sourced from multiple suppliers. Other in-feed products supplement the vitamins and minerals necessary for maximised calcium absorption and function. Some even contain ingredients that will directly support intestinal health. In practice, a combination of product types seems to work best, especially when used at the appropriate time; calcium and vitamin D3 supplementation with intestinal health support products.

As with most things, planning is key, and managing shell quality is no different. Application earlier in the production cycle (given the trend for longer-lived flocks) is most beneficial. This can be tailored accordingly once egg size and peak production have been established. Feedback from the packer provides some objective insight into shell quality, but technology is now in existence that easily facilitates shell strength testing on-farm. Measuring shell strength is a useful way of assessing how well competing products work, and therefore helps tailor choices more precisely, whilst also facilitating a cost-benefit analysis more easily. Shell support products vary considerably in price, so understanding which products your birds benefit from most, is a key factor in managing flock finances.

In summary, there are many factors influencing the shell, most of which work over an extended term. Therefore, correcting abnormalities in shell quality can be challenging, so a planned approach to managing shell is necessary, especially in the longer-lived flocks. Recognising that shell quality is not just a direct result of “shell supplements” is crucial when choosing the right product(s) for your flock. Appreciating that shell quality positively correlates with overall bird health, particularly that of the intestine is crucial to understanding how best optimise egg quality for each flock.

Originally written for The Ranger magazine.

Browse by category