Soft or missing egg shells are quite common in older birds, especially high production hybrids and especially as they come out of lay for the season.
In younger hens, sometimes an egg stays in the shell gland for too long (see calcium coated shells) and the egg that follows it doesn't spend long enough. In these circumstances, the two eggs are laid closely together on the same day.
Thin egg shells can occur on hot days when the temperature rises. This is associated with a lower food intake and shell thickness will return to normal when the temperature drops and the food intake returns to normal.
A 'soft shelled egg' is one that has a membrane but no shell. Most people immediately think that Oyster shell grit (shown right) is what a hen needs if she is laying soft shelled eggs but a dietary deficiency can also be the cause of a ‘soft' shelled egg. Whilst chickens need calcium in their diet which can be provided by soluble grit (such as Oystershell) to form egg shells, sufficient calcium can usually be found in modern formulated poultry feeds.
Chickens need the correct level of protein in their diet as well as minerals and various other vitamins. Vitamin D3 (Cholecalciferol) for example is used for the metabolism of calcium and phosphorus so that they are able to form egg shells as well as strong bones. Vitamin D is found in Cod Liver Oil but they shouldn't normally need this if they are fed the correct formulated layers feed, are free range and have sunshine on their backs.
Soft shelled eggs laid once in a while are nothing to worry about. Hens that are at the start of their laying period, or have come to the end of it, often lay a soft shelled egg.
Wheat found in mixed corn typically contains about 10% protein. This isn't a sufficient amount for a hen that is producing eggs. Keep corn as a treat only. Feeding household scraps is technically no longer allowed by DEFRA but if you feed 'allotment scraps', they can be a bit of a mixed bag of what a hen needs so whilst this is a way to save on feed costs, scraps should not really exceed 25% of a hen's diet. Allotment scraps should be mixed with layers mash to make a crumbly mixture. The best way to ensure a hen is getting the correct diet is to use a balanced layers feed and then supplement this with greens and a vitamin and mineral drink that can be added to their water during the peak months of production.
If hens can be allowed to free range on grass or rough ground then this is much better than having to add top up vitamin and mineral drinks. They will be able to pick up a lot of the extra grit, vitamins and minerals they need and be a lot less prone to health problems as well as soft shelled eggs.
Some strains of birds can lay more soft egg shells as they age. This is particularly true of hybrid breeds that have been optimised to give as many eggs as possible during their first year such as the Bovan Goldline often found in ‘battery' farming. Once these birds reach 4 or 5 years old, you may find they start to lay eggs with soft shells. If you are keeping ex-batts then our section of Rehoming Ex-Battery Hens has a number of articles, specifically for ex-battery hens and their needs.
If diet doesn't seem to be the problem and soft shelled eggs are being laid regularly during the middle of a laying period, then there could be a number of reasons for this: