Good quality chicks from disinfected eggs

As a central link between multiplication and production level, the hatchery has to ensure the best potency of production for the level below. Egg disinfection is a means of reaching that goal. This is a non-sufficient but compulsory part of the chick quality, and as such it has to follow accurate guidance, starting at the farm already.

By Dr Vincent Turblin , CEVA Animal Health, France

Nowadays, good cleaning and disinfection practices are widely acknowledged as part of the optimisation of the viable day old chick (DOC) production in a hatchery. Good egg hygiene has often proven to improve the viability and the quality of the DOC. Indeed, a strong bacterial penetration through the egg shell will affect several aspects in hatching quality, like early embryonic mortality, egg yolk infection, DOC mortality before hatching, besides a significant higher mortality and heterogeneity of the chicks during the first week of age.

Vertical and horizontal
Clearly, various micro-organisms can contaminate the hatching eggs in different ways. Vertical contamination will involve the reproductive tract of the hen, including the last part of it which is shared with the digestive tract (the cloaca). Thus, this vertical transmission of the pathogens could be pedagogically divided into two different ways of contamination of the hatching eggs:

· Transovarian transmission, in which the micro-organism is already located in the ovules even before the ovulation. SP and SG are probably the most well known examples of this kind of transmission.

· Contamination of the surface of the eggshell and thus penetration of the pathogen into the hatching egg. It occurs either during the oviposition through the contact with the cloaca of infected hens or immediately after through contact with contaminated faeces and litter. SE and ST can be considered as examples of such ways of vertical transmission.

Source inside hatchery
Horizontal contamination needs a source inside of the hatchery; a kind of reservoir from which air, water or manipulation of the eggs will spread the micro-organisms to the hatching eggs by direct contact. This is the case for E.coli, Pseudomonas and Staphylococus.

It is important to consider that the environment of the laying house will deeply influence the shell cleanness. Even the quality of the digestion of the hens can also interfere with the quality of the egg (contamination aspect besides all the other nutrition transfers to the DOC). Indeed, after oviposition, those eggs non-contaminated vertically will still remain susceptible to the health status of the breeder flock (Salmonella) and to the pressure of bacteria responsible for hatching-egg putrefaction like Pseudomonas, which will be enhanced in diarrheic flocks.

Bacterial penetration
An intact cuticle is commonly acknowledged as an efficient barrier against penetration. Nevertheless, the immature cuticle of freshly laid eggs could be easily penetrated. Moreover it has to be considered that these freshly laid eggs will be in contact with tough materials on the nests or even the hens themselves can cause scratches on them, so it is a critical stage in bacterial penetration. Besides, there are thousands of pores on the egg shell which are essential for exchange of gases. Most of them are covered by a cuticle preventing liquid and bacterial penetration, but several others are not and thus allow the penetration of micro-organisms into the eggs.

Furthermore, it has also to be considered that, after the oviposition, eggs will switch from a 40°C temperature to an ambient one. During this process, they will dry and cool down, creating a pressure gap through the egg shell. In order to balance inside and outside pressure, the air will be “sucked” through the pores and therefore increasing the bacterial penetration (Figure 1). As a result, the production of healthy hatching eggs is the result of strict sanitary prophylaxis managing of all the steps, from the breeder stage to the hatchery itself.

How to disinfect hatching eggs
Immediate application of the sanitiser as soon as the eggs are collected is of utmost importance. Failure to apply the sanitiser in a timely manner will give the opportunity to the bacteria to penetrate into the hatching eggs through the pores of the eggshell, thus reaching the shell membrane. Inside the eggs, the microorganisms will not be exposed to the sanitiser any more and, during the incubation process, they will find the ideal condition to multiply in the egg’s interior. Therefore, the disinfection aims at destroying the microorganisms before they enter into the egg.

Choosing the disinfectant
The disinfectant used, in itself, must fulfil different requirements: to have a broad spectrum (to be able to destroy a wide range of micro-organisms, from Gram -ve to Gram +ve and moulds), to be active at a low concentration, as safe for human users as for eggs, chemically stable, without any corrosive action on metals, and comply with local regulations. Moreover, it is necessary to take into consideration that different factors will influence the activity of a disinfectant such as the kind of surface and its status, the bacteriological and physico-chemical properties of the dilution water, the concentration and the temperature. Each family of disinfectants has its own characteristics and their activity spectrum is relatively specific.

According to the terrestrial animal health code of the World Organization for animal health, there are three major ways of egg disinfection: fumigation, spraying and dipping.

Proper fumigation procedure
Clearly, only exposing the hatching eggs to formaldehyde is not enough to sanitise them. In a proper fumigation procedure, five different factors have to be taken into consideration: concentration of formaldehyde, temperature, humidity, time of exposure and circulation of the gas. No consensus is really established currently on the optimum concentration of formaldehyde required. Usually, three levels of concentration have been used and two different methods have been adopted. As the formaldehyde gas rapidly loses its efficiency in low temperatures and dry atmosphere, the control of these two parameters is critical. In that way, the temperature and the relative humidity inside of the chamber should be kept between 24°-38°C and 60-80%, respectively.

To complete the procedure, the time of exposure to the disinfecting agent should be 20 minutes. Moreover, it is crucial to circulate the gas in order to make sure that surfaces of the egg shell will have contact with the disinfecting gas. After this procedure, the gas should be expelled in a safe way.

Safety measures critical
Finally, in order to ensure the efficacy of the whole process, the hatching eggs should be placed on wire racks, in wire baskets or on cup-type egg flats stacked in a manner that will permit air circulation and exposure to the formaldehyde gas.

Nevertheless, during the fumigation process, safety measures are critical and must be followed carefully. Some of these precautions include avoiding the use of plastic or polyethylene containers as the heat generated by the chemical reaction could set fire in those materials. Besides, to avoid possible fire hazards, the containers should slope outwards. It is also important to use containers large enough so that the two chemicals occupy no more than one quarter of its total capacity (volume). Preferably, the container should have a capacity of at least ten times the volume of the total ingredients. Furthermore, the operator is advised to use a mask in order to prevent irritation of the eyes and nose.

Alternative solutions
Even though formaldehyde has always been used as the product of choice for a long time, it remains the disinfectant of choice for hatching eggs. In the hatcheries, no embryonic mortality is observed under good practices of use. Moreover, used as fumigation, formol vapours show real efficacy to destroy microorganisms on the shell, the box, the hatching machines or every material used (only if, obviously, they are previously cleaned). Another explanation is nevertheless its relative efficacy in presence of residual organic matter. Besides, it seems that few cases of resistance of micro-organisms against formol have been found.

However, research is no longer focusing on this molecule since, in some more regulated countries, it will belong to the past as the International Agency for Research on Cancer (IARC / WHO) pointed out this molecule as carcinogenic for human beings. Several countries are thus looking for alternative solutions for egg disinfection, to replace the undesirable characteristic of this disinfectant, but keeping its efficacy.

Requirements for spraying
As for any disinfecting procedure, the spray method has to follow some requirements in order to properly sanitise the eggs:

· Selection and dilution of the disinfectant: besides some other criteria related to the activity of the disinfectant (Table 1), do not use any compound which can impair the exchange of gases through the eggshell.

· Correct application: to kill as many organisms as possible, the disinfecting solution has to be applied in a manner which will thoroughly wet the shell surface. Undoubtedly, this is one of the limitations of this method of disinfection as it depends on the proper spraying and, at the farm level, it is not unusual to find that the bottom of the eggs were not reached.

· In very cold weather, in order to avoid any thermal shock, it is advisable to heat up the water before preparing the disinfecting solution and spraying it on the eggs.

Very careful dipping
This method must be carried out very carefully. The temperature, for the reasons seen before, has to be monitored strictly to avoid any risk of a temperature shock. Especially after dipping dirty eggs, the dirtiness remains in disinfectant solution and it can induce:

· lower activity of disinfectant

· contamination of other batches of eggs

In order to avoid these problems, a pre-selection of the eggs before dipping is required (do not dip dirty eggs) and change the disinfecting solutions often (at least once a day).

Implications of improper sanitising
Proper selection and use of a sanitiser is essential for good sanitation management and can prevent additional problems in the hatchery, especially when the bacterial population on one eggshell can reach 300,000 CFU instead of about 300 on a sanitised shell. Since most incubators have greater than a 40,000 egg capacity, thousands of eggs and chicks could become contaminated if an infected egg explodes, breaks or becomes cracked inside the incubator. The proper practice of good management strategies will prevent microbial problems and aid in the production of quality chicks.

Hygiene measures during the handling of eggs and day old chicks
(source: OIE / WHO)

1. Egg handlers in the hatchery should wash their hands with soap and water and change to clean outer garments before handling hatching eggs received from the poultry farm.

2. Chick sexers and chick handlers must wash and disinfect their hands and change into clean protective clothing and boots before commencing work and between different lots of chicks.

3. Day old chicks or other poultry must be delivered or distributed in new chick boxes; or in used boxes made of suitable material which have been thoroughly cleaned and disinfected or fumigated.

4. The chicks should be delivered directly from the hatchery by personnel wearing clean, disinfected outer clothing. Outer clothing should be changed or disinfected between each delivery.

5. The delivery truck must be cleaned and disinfected before loading each consignment of chicks.

Recommendations applicable to hatching egg hygiene and transport
(source: OIE / WHO)

1. The litter in the laying house should be kept dry and in good condition. The nest box litter should be clean and adequate in quantity.

2. Eggs should be collected at frequent intervals of not less than twice per day and placed in clean disinfected containers.

3. Dirty, broken, cracked, leaking and dented eggs should be collected in a separate container and should not be used for hatching purposes.

4. The clean eggs should be sanitised as soon as possible after collection.

5. The sanitised eggs should be stored in a clean, dust free room used exclusively for this purpose and kept at a temperature of 13-15°C (55°-60°F) and at a relative humidity of 70-80%.

6. The eggs should be transported to the hatchery in new or clean cases which have been fumigated or sanitised with a liquid disinfectant. The cleaning and disinfection of vehicles must be a regular part of the hatchery routine.

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