The eggshell is riddled with pores which allow oxygen to enter the egg and carbon dioxide to exit. Eggs need to loose weight during incubation and water vapor also leaves the egg through the pores.

The cuticle, the outer layer of the eggshell is the first defense of an egg. It helps prevent water and contaminants from entering the pores.

The environment that the egg encounters within the first few seconds after it is layed is critical. At this time the egg is wet and its pores full of fluid. If the shell comes in contact with a dirty surface the film of water on its surface provides the ideal route for bacteria, viruses or fungi to enter the pores and move inside the egg. Once the contents of an egg are contaminated, cleaning and disinfecting the shell will not remove the problem. So good nest hygiene and prompt collection of eggs are crucial.

Backyard flock hygiene

Prevention is the best control to reduce the number of dirty eggs.

• Most eggs coming from nests should be clean if the nesting materials are kept clean.
• The production of floor eggs can be minimized if the flock is trained early to use its nest boxes by adding a few fake eggs.
• Eggs should be gathered at least once a day or more often. The longer eggs are left in nests, the more likely they may be broken or dirtied. For poultry, nests should be cleaned once a week to remove dirty litter and manure, and replaced with clean bedding materials. More often for waterfowl.

Even under the best conditions, some dirty eggs may still result. Dirty eggs should be placed in a separate container so they don’t contaminate clean eggs.

So should eggs be cleaned before setting in an incubator?

Not necessarily. In many cases you could do more harm than good for a couple of reasons:

• All sanitizing procedures will remove the outer cuticle from the egg as well as the dirt and may leave the egg at greater risk from bacterial contamination.
• Any cleaning procedure incorrectly followed can contaminate the egg rather than sanitize it.

Cleaning procedures

Cracked eggs should be discarded if possible and should not be wet cleaned.

Dry cleaning with abrasives is an option for lightly soiled eggs but you run the risk of breaking the egg. It is time-consuming and weakens the cuticle. The fine dust created by abrasion can also be pushed down into the pores, partially blocking them and causing respiratory problems particularly towards the end of incubation.
Dry cleaning doesn't work very well to clean up eggs that have been smeared with the contents of broken eggs in the nest.

If you choose to use abrasives to clean the eggs, remember to sanitize them from time to time in water with bleach, and to allow them to dry fully before use to avoid the same issues as wet cleaning.

Wet cleaning is more complicated. Poor practice has given egg washing a bad name because it can cause more problems than it was designed to solve.

The basic issue is that dirty eggs are covered with bacteria, which have trouble getting through the shell so long as it remains dry. As soon as the shell is wet, they pass through the shell more easily.

Soiled eggs may be cleaned using a brand egg wash solution such as Brinsea Incubation Disinfectant Concentrate following the manufacturer’s instructions but it is essential to wash eggs in solution which is significantly warmer than the egg otherwise dirty water will flow inwards through the pores and contaminate the inside of the egg. If you cool the egg, the contents shrink slightly, causing a partial vacuum inside which tends to pull foreign matter into the egg.

Ideally eggs should be washed in a solution at (105°F - 41°C) and rinsed in another solution also at (105°F - 41°C) before being set to dry on a clean surface. Thereafter they should only be handled with clean hands.

Egg washers with thermostatic control are available to ensure the solution is maintained at the correct temperature.

Problems to watch out for:

Washing solution too hot (over 122°F – 50°C) and immersion for too long can damage the embryo. The egg contents will warm considerably and the egg will take some while to cool after it is removed from the solution. The embryo temperature may reach such a level that it starts developing but not at a rate that can be sustained long enough for normal development. Particular care should be taken with small eggs.

Washing solution too cold (under 104°F – 40°C). The air the pores will contract and pull some of the washing solution inside the egg. The embryo may be damaged by the solution itself or if the solution is inactive by bacteria.

Washing all the eggs in the same solution. You should wash the cleanest eggs first leaving the really dirty eggs for last. It is always best to change the solution regularly rather than trying to add more disinfectant to an already dirty solution.

Wearing gloves. Rubber gloves can be slippery when wet and can easily get contaminated. It is preferable to use freshly washed hands to handle eggs.

Conclusion

Any sanitizing procedure will weaken the egg’s natural defense against contamination and should only be undertaken with great care.

For small scale production:

• Heavily soiled eggs should be discarded if possible.
• Unsoiled eggs are better handled as little as possible and not sanitized before incubation.
• Soiled eggs can be carefully dry cleaned or, if wet cleaned, only washed in solution significantly warmer than the egg.

For more information on egg handling procedures before incubation please refer to
our storage and handling guidelines because the quality of a chick all depends on the quality of an egg.