Could red skin be link to white eggs?

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The red skin developed by free range birds that have lost feathers could be a crucial link to the cause of white eggs.

This is the theory to emerge from a Defra-funded investigation into the white egg problem that blights the performance of hundreds of flocks every summer.

The new research work was carried out jointly by ADAS, the Scottish Agricultural College and the St David's Farm and Equine Veterinary Practice, based near Exeter.

The report points out that if just one per cent of eggs are downgraded as a result of white shells then in just three summer months that would involve 400,000 dozen eggs. The cost to producers would reach £150,000.

A wide range of causes has been said to lead to the problem including stress, disease, feather loss and exposure to sunshine or heat. But most of these ideas are confounded by the fact that there is one sure way to solve the problem—shutting the birds in for three or four days which, of course, means the eggs lose their free range status.

The researchers took a four pronged approach to trying to pin down the real cause. They carried out a major review of the scientific literature, gathered information from producers and vets, carried out shell colour monitoring at packing stations and studied conditions on seven farms which had a white shell problem.

Previous research shows that the colour of an egg shell is created by what are called porphyrins, derived from a parent compound called porphine. But just how and at what stage the hen applies this substance remains unclear. It has been established that a large proportion of the colour is contained in the cuticle.

But previous studies have also revealed what may be a significant side-effect of feeding the anti-coccidiostat Nicarbazin.

Within three days treated birds begin to lay white eggs. The effect disappears about three days after withdrawal, the same period of time it takes to solve a white egg problem by shutting birds off the range.

This effect, says the report, may therefore provide a clue to the mechanisms involved in the loss of shell colour.

"Published papers suggest," it says, "that whilst Nicarbazin does not affect porphyrin synthesis it may block chemical pathways and affect concentrations of porphyrin found in specific tissues in the body."

Which is where the skin colour comes in. All of the problem flocks studied had suffered feather loss and the exposed skin on the body, legs and around the eyes had "noticeably reddened". This is a phenomenon which has not been previously noted in cage flocks which have lost feathers, say the researchers.

Could this redness be the result of porphyrins being diverted to the body tissue instead of being used to colour eggs?

"The possibility that hens may be consuming range vegetation that contains naturally-occurring compounds which may exert the same effects as Nicarbazin cannot be ruled out," says the report. "However, partitioning of the porphyrin may naturally occur in some free range flocks when they are in direct contact with sunlight. The effects of viral disease and the rate of feather loss may be contributory factors.

"It may be hypothesized that a visual indicator of this process is the development of a reddened skin colour in free range hens that does not appear to develop in hens that lose feathers indoors."

Certainly the research was able to rule out many of the other theories for white shells. Corticosteroid tests did not suggest that stress was a significant factor, the breed of the birds appeared to be irrelevant and cuticle loss was ruled out. So was the possibility that white eggs are normally coloured eggs in which the cuticle is covered by a layer of white calcium phosphate.

Mycoplasma did not appear to be a factor and ART appeared on just two sites. No flock was in the grip of disease. However, evidence of variant forms of infectious bronchitis was "consistently high".

"An association between white eggs and variant forms of IB is already well documented," says the report, "and it is possible that these may have an effect upon the oviduct as well as on kidney function and possibly on the rate of feather loss."

The report suggests further research work to discover if the red skin theory can be proved. It says there is a need to establish whether the skin redness persists all year and if it is linked to biochemical changes involving porphyrins.

It also wants more investigations of feather loss and in particular whether the presence of variant IB early in the laying cycle may predispose birds to early loss of feathers.