Dirty eggs and broken eggs are the main causes for egg rejection. In breeding hens, the percentage of dirty eggs should not exceed 1-2%. The objective is to reduce the percentage of dirty eggs to the minimum, to be able to discard this type of eggs instead of incubating them.

The obtention of clean eggs is a relevant issue for the egg industry, as it allows to sell the commercial eggs, where the eggshell quality, including colour and cleanliness, is essential to access the market.

Obtaining a clean egg is also of great importance in breeding hens. When dirty eggs are incubated, the chances of producing a viable chick are reduced, since the microbial load is high.

This article discusses the different causes of dirty eggs appearing in laying and breeding hens, either producing in cages or in soil.

Causes of dirty eggs

There are multiple factors that may cause the appearance of dirty eggs. These factors are often interrelated, being the most important ones:

• Training process of the pullets and hens to lay in the nest.
• Age of the hen.
• Nutrition
• Sanitary status
• Facilities: environmental conditions, nest, litter, feeding and drinking system
• Management and hygiene plan

• Training process of the pullets and hens to lay in the nest

An incorrect learning on the use of the nest to lay may result in an increase of eggs laid in the litter and, consequently, a greater probability of internal contamination of the egg.

Eggs laid in the litter should not exceed 2-3%. At the beginning of the laying period, this percentage may be higher, but this problem must have been solved in the laying peak.

• Age of the hen

Hens may have a greater number of dirty eggs at the beginning of the laying phase due to a higher percentage of eggs laid in the litter, since they are still learning to lay in the nest.

It should also be noted that, as the age of the birds progresses, the quality of the shell decreases, becoming more fragile and porous. Dirty eggs laid at the end of the laying cycle are more porous, so they are more likely to be internally contaminated.

• Nutrition

There are different nutritional factors which can lead to a lower consistency of the stool. Nutritional disbalances or sudden changes in feed may cause a non-pathogenic diarrhea that dirt the egg.

The first factor is the composition of the diet, since certain cereals, rich in non-starchy polysaccharides, such as rye, increase the viscosity of the diet. Higher viscosity of the intestinal content favours the appearance of pasty faeces, which may stain the cloaca and the egg.

A sudden change in the formulation can also produce an intestinal imbalance that affects the consistency of faeces.

Additional factors that should be considered are a high inclusion of mineral salts or a product rich in monosaccharides, which may lead to excessive water secretion in the gut and the appearance of watery stools.

• Health

Watery faeces are usually related to agents that cause dysbacteriosis or intestinal lesions, such as stress situations (i.e.: sudden temperature changes), mycotoxins, or some infections with digestive processes, whether of bacterial origin, such as necrotic enteritis, viral origin, such as rotavirus, or protozoan origin, such as coccidiosis.

These infectious agents may be previously present in the facilities due to incorrect disinfection and cleaning, but they can also access the farm due to incorrect handling of operators and visitors, or because of poor microbiological quality of feed or water.

• Facilities

1. Environment

Any disruption in the environment can lead to laying out of the nest and higher probability of dirty eggs appearance.

Poor ventilation of the facility, with strong air flow areas, may change the laying area to outside the nest. The same occurs when lighting is not properly located, as hens find dark areas in the litter which are used as a nest.

1. Nest

Poor condition of the nest or unattractive nests may favour eggs laid in the litter and dirty eggs.

1. Litter

Excessive litter provides an alternative space for laying and increases the risk of the egg contamination.

In addition, a poor litter status will dirt hens feet. The dirt in the feet will be transported to other parts of the farm, like the nests, and will increase the incidence of dirty eggs.

1. Feeding and drinking system

When there is a reduced number of feeders or drinking fountains, or their space is not enough for all animals in the farm, there will be an increase in competitiveness to access to feed or water. Therefore, animal will sacrifice its access to the nest to be able to drink and feed, increasing the risk of laying in the ground and egg contamination.

The location of the drinking and feeding system may also block the access to the nest and cause the same effect mentioned above.

Inadequate maintenance of the drinking systems, and the consequent loss of water, can moisten the litter and favour the contamination of eggs laid in the litter, a part from dirtying the feet of the animals.

1. Hygiene and handling

High density in the farm may compromise the access to the nest, increasing the probability of laying in the litter and the risk of egg contamination.

A bad litter status will have an effect on the nest, the mats and the tape, and eases the egg to get dirty. In addition, it facilitates the survival and subsequent transmission of multiple infectious agents, which can affect the digestive system and aggravate the situation.

Preventive and corrective measures

A combined approach should be planned, in order to work with measures for each determining factor, which will help to obtain better results than if only one measure is taken. Therefore, the prevention of this phenomenon should be based on each of the possible causes mentioned.

• Training process of the pullets and hens to lay in the nest

It is important to teach birds to use nests to avoid the presence of eggs in the litter, potentially dirty.

Before starting the laying period, if there is a mechanical collection system, it is recommended to run the system several times a day so that the birds become familiar with the noise and avoid any fear to enter the nest.

An operator should walk inside the facilities several times a day, at least 4 times, especially at the beginning of the laying period. The operator will make the hens climb to the slats, will place inside the nest any animal laying in the litter and will collect eggs present in the litter. It should be noted that hens lay the eggs in areas where there are already laid eggs, thus, eggs should be removed from the litter to avoid accumulations.

When the percentage of eggs laid in the litter is greater than 2-3%, possible causes should be reviewed and solutions applied to solve the problem.

• Animal age

Training of the animals during the start of the laying period will reduce the rate of eggs laid in the litter at the end of the production period, when eggshell is more fragile and porous and eggs are more susceptible to contamination.

• Nutrition

As mentioned, diarrhea derived from nutrition is not pathological, so animals do not need medical treatment, but the formulation must be carefully reviewed. There are different nutrition-related measures that can be taken to reduce the risk of dirty eggs.

Regarding feed ingredients, inclusion of cereals rich in non-digestible fiber should be reduced, or they should be replaced by cereals with a lower percentage of non-digestible fiber, such as corn or wheat. When there is no alternative source of cereal than rye or other cereals rich in non-digestible fiber, enzymes can be added to increase the digestibility of this type of cereals. In addition, a gradual transition must be made between different feed formulations.

• Sanitary status

Biosecurity and hygiene measures should be applied in the farm to prevent the proliferation of infectious agents, as well as monitor the microbiological quality of feed and water, in order to avoid digestive infections that may change the consistency of faeces and dirt the egg. After an outbreak, the correct elimination of the agent must be ensured to avoid recurrence of the disease between batches.

It is advisable to inclue support measures to ensure adequate intestinal health of animals, such as the administration of probiotics or products of plant origin that maintain the balance of the digestive flora and intestinal integrity, as well as the use of mycotoxin binders to prevent damage to the digestive mucosa.

• Facilities, cages

1. Environment

Intensity of the lighting and ventilation must be correct and homogeneous in the facility, to avoid dark or warmer areas that can be an alternative area to the nest.

The control of temperature and ventilation will also prevent stress situations that alter the intake of food or water and lead to dysbiosis and diarrhea.

1. Nest

Obtention and maintenance of a good status of the nest is essential to ensure hens are not laying in alternative places. Nests must be attractive to females and have a wide entrance to facilitate the access of animals. Eggs laid outside the nest have a higher risk of contamination and becoming a dirty egg.

Nests should remain closed until first eggs are laid. Once in the laying phase, they must remain closed while the lights are off, to prevent birds from sleeping in them. Thanks to this method, hens relate the nest as a suitable place only to perform the activity of laying.

1. Litter

Alternative places used for laying in the litter should be removed. Excess of litter material should be avoided, especially at the beginning of the laying phase. When laying in the nest is ensured, more litter material can be included.

1. Feeding and drinking system

Assessment of the behaviour of hens during feeding should be performed, in order to identify any possible issue regarding space in feeders or blocked access to the nest.

If possible, feeders should be raised when not in use to avoid problems of access inside the nest. In breeding hens, it is also necessary to evaluate where male feeders are placed. It is advisable to place male feeders away from the nests area, to prevent them from blocking the access to the nest.

Investment in new materials in the facilities must have prior proper advise to prevent the new measures from being detrimental to production.

1. Hygiene management and plan

An adequate density of animals, according to the space in the facility, must be ensured.

Nests, mats and tape should be cleaned and disinfected regularly.

Litter should be kept dry to prevent hens from dirtying the mats and nest with their droppings. Ventilation system and drinking fountains should be checked frequently to ensure that the bed does not get wet.

Conclusions

It is essential to produce clean eggs to access the market, as well as to obtain chicks of good quality.

Main factors to consider when assessing the incidence of dirty eggs are: eggs laid in the litter and consistency of faeces. There are many possible issues causing these two factors, and they are often connected to each other: management and hygiene, facilities, nutrition or sanitary status of the batch.

Therefore, many approaches can be performed to solve the problem. A combination of measures to avoid laying in the litter and to ensure proper intestinal health is the best way to achieve the desired goal.

It is of great importance to train hens to lay in the nest, in addition to offering adequate facilities, both in design and hygiene, a controlled environment, a correct density of the animals, a quality and balanced feed, as well as a good preventive medicine plan to avoid any infectious process.

In breeding hens, monitoring of the quality of the chicks in the hatchery will allow a continuous evaluation of the efficacy of the plan and the application of additional measures to solve the critical points if needed.