Contamination of Hatching Eggs

Poor hatching egg sanitation can be a major cause in loss of hatchability and chick quality. Every effort should be made to ensure that hatching eggs are kept as free as possible from risks of contamination from the time of egg laying until the chicks are pulled from the hatcher.

There is no such thing as a sterile eggshell. Eggs removed from the oviduct have some bacteria. More bacteria are picked up on the shell when the egg passes through the cloaca where the urinary and intestinal tracts also enter. From 300 to 500 bacteria may found on an eggshell at the time of lay.

Then, every surface the egg comes in contact with can further inoculate the shell surface. It is very important to maintain clean nest litter to prevent further contamination. Remove fecal material from the litter and replace the litter about every two weeks. The condition of the floor litter will influence the amount of filth the hen brings into the nest on her feet. Eggs laid on the floor will have thousands of bacteria even if the shell appears to be clean.

Table 1 shows the relationship in shell surface contamination with subsequent two-week chick mortality after hatching. Compare the two week chick mortality percentages. Slightly soiled eggs resulted in more than double the chick mortality as nest clean eggs and for dirty eggs the two week chick mortality more than quadrupled that of chicks hatched from nest clean eggs.









After an egg is laid, it begins to cool. During the cooling process the egg contents begin to shrink producing internal suction. This is one of the more opportune times for the bacteria on the shell surface to penetrate.


Egg's Natural Defense Against Bacterial Penetration

The egg has some natural defense mechanisms to reduce bacterial penetration. The shell itself provides some protection. Although the normal eggshell will have about 8,000 pore openings, most of the pores are too small in diameter for bacteria to penetrate. However, there are always some pores large enough to accommodate penetrating bacteria. Shell quality and thickness are two very influential factors which affect penetration. E.F. Sauter and C.F. Peterson demonstrated that shell quality has more influence than time for bacteria to penetrate (Table 2).

The cuticle on the surface of the eggshell is the best natural barrier to penetration. However, there is variation in cuticle thickness even on the same egg and the ability of the organisms to penetrate varies according to cuticle thickness.

The inner and outer shell membranes provide additional barriers. Many times bacteria will penetrate the pores of the shell and get trapped between the outer and inner shell membrane and go no further. This is no consolation because these bacteria can infect the embryo as it pips through these membranes and the shell. Plus, after hatching these infected membranes are exposed to the healthy chicks in the hatching tray.

The albumen provides a somewhat effective control over contamination. The albumen has a high pH in which most bacteria cannot survive. The yolk membrane (vitelline) does not prevent bacterial contamination.


Methods of Hatching Egg Sanitation

Management that encourages the production of nest clean eggs is probably the best form of hatching egg sanitation. Many producers choose to go the extra step by providing other means of sanitation. Whichever method is chosen, the critical factor is time. The earlier the eggs are sanitized, the better. Bacteria have been reported to penetrate an eggshell in less than 30 minutes after lay.

Sanding, buffing, and wiping hatching eggs are not good methods of sanitation. Sanding and buffing will remove at least part of the cuticle resulting in eggs that are more susceptible to penetration. The sanding process itself may actually grind the bacteria further into the shell. The general rules for sanding, buffing or wiping is that to: never exceed one wipe to remove material on the shell; and don't do it.

Fumigation with formaldehyde gas has been an effective method of hatching egg sanitation. The procedure is to generate a 3X dose of formaldehyde in an air-tight egg holding cabinet or room for 30 minutes. The formaldehyde provides excellent bacterial kill on contact and it is very easy to fumigate a large number of eggs at a time.

One of the deficiencies of formaldehyde fumigation is that it cannot be administered as soon after lay as some other methods of hatching egg sanitation. Another is that its use is now restricted in the US by the Occupational Safety and Health Administration as a possible carcinogen. Other countries are beginning to restrict the use of formaldehyde.

Hatching eggs may also be fumigated with ozone provided by ozone generators. This method, to date, has not been widely used.

Hand-spraying hatching eggs with a disinfectant is sometimes a moderately effective measure. Solutions of quaternary ammonia, formalin, mixtures of quaternary ammonia, and formalin or phenols have been used for egg sanitation. Some of the drawbacks for hand spraying include low pressure, incomplete shell surface coverage and no temperature control for the disinfectant. All disinfectants work better when the solution temperature is high (>110ºF or >40ºC). Additionally, those eggs with adhering organic matter are not properly sanitized with hand spraying.

A few decades ago, immersing hatching eggs in a vat with heated disinfectant was used to sanitize hatching eggs. Although the procedure was shown to be very effective, it did not work well on a mass basis. Many producers who tried this did not change the solutions frequently enough and caused more contamination than they prevented. The recommended time of immersion was five minutes and there were many instances when the eggs were left in the tank too long resulting in elevated yolk temperatures and lower hatchability. Leaving them in the disinfectant solution too short a time causes inadequate sanitation. The lack of proper temperature control was another major drawback. After repeated immersions the temperature of the solution would fall to ineffective levels. In short, immersion dipping proved to be a very ineffective and even harmful procedure for hatching egg sanitation and has resulted in a bias against hatching egg sanitation in the U.S.

Immersion dipping, if tightly monitored, is effective. There are parts of the industry where it is still in use as an effective sanitation procedure. It appears to be more effective when sanitizing the more expensive eggs such as turkey or primary breeder eggs. The reason for its success in these situations is probably due to the extra care in implementation that the more expensive eggs require.


Mechanical spray sanitation of hatching eggs

The turkey industry has been using mechanized spray sanitation for hatching eggs for many years. Mechanical egg washers are able to avoid the pitfalls (solution temperature, timed exposure, and fresh disinfectant solutions) commonly experienced with immersion dipping and hand spray sanitation. Earlier models of mechanical egg washers only sanitized one egg at a time and used brushes to aid in the cleaning process.

The broiler hatching egg industry has been reluctant to try mechanical egg washing because: a bias against wetting the egg even with a disinfectant due to earlier problems with immersion dipping; washing one egg at a time is not time efficient in broiler breeder flocks where many more eggs are produced each day than in the typical turkey breeder house; the value per egg of broiler hatching eggs is much less than with turkey eggs; and the fear of removing the egg�s cuticle protection by the brushes. The turkey industry favors hatching egg washing which offers some degree of cuticle removal with the washing with brushes. This may have provided more moisture loss during incubation. The broiler hatching egg industry has not shown a benefit for cuticle removal.

Currently, there are several models of mechanical egg washing machines that can wash one plastic flat of eggs at a time and do not use brushes. These machines have conveyors which are wide enough for plastic flats to pass through the wash and spray cycles. The spray is provided by nozzles placed above and below the egg flats. The temperature of the wash solutions are precisely maintained during washing (the machine will automatically stop when the temperature rises above or fall below the desired temperature range). The typical hatching egg washing machine will have at least two liquid tanks; the first containing a wash solution with a sanitizer such as chlorine or hydrogen peroxide, and the second will contain a disinfectant such as quaternary ammonium, phenol, or hydrogen peroxide. In the first tank, the wash solution (temperature 111ºF; 44ºC) is recycled after filtering and the metering in of additional sanitizer. In the second tank, there is no recycling, only a fine mist spray of the disinfectant solution.

These machines are very convenient for hatching egg production since flats of eggs can be sanitized immediately after collection and loaded directly into the hatching egg buggies before being moved to the egg storage room. They work well with both conventional and mechanical nesting systems.

Nest clean hatching eggs are passed through the machine once on high speed. Very few eggs will be more than three hours old at the time of sanitation, a considerable advantage. After the last of a collection of eggs has been run, most of the floor eggs can be salvaged by passing them through once on slow speed and then a second time on high speed. Floor and dirty eggs showing no adhering debris after washing can be sent to the hatchery as hatching eggs.

In a 12,000 hen broiler breeder flock field study in Georgia, salvaging most of the floor eggs through mechanical egg washing resulted in an additional case of hatching eggs being sent to the hatchery per week. Floor and dirty eggs are normally sold as commercial eggs with a value of about $5.70 per case while a case of hatching eggs is worth about $37.00 per case. During 40 weeks of production, salvaging an extra case of hatching eggs per week resulted in more than $1,000 in additional net income for the grower. The main benefit of mechanical egg washing, however, is not to salvage floor and dirty eggs but to improve sanitation of all eggs and flats entering the hatchery.

In the Georgia field study with a mechanical egg washer (Cox, N.A., J. S. Bailey, M.E. Berrang, R.J. Buhr, and J.M. Mauldin, 1994. Journal of Applied Poultry Research 3:234-237), both nest clean and dirty eggs exhibited reductions in shell surface contamination by more than 99% while hatchability performance remained unchanged (Table 3). Examination of sanitized and non-sanitized eggs through electron microscopy revealed that very little cuticle loss occurred due to the washing procedure and yolk temperatures were not elevated.

The main drawback to mechanical egg washing on the farm is its expense. For optimum results a mechanical egg washer would have to be placed in every breeder house. The mechanical egg washer could be used in the hatchery to reduce the expense of purchasing one for each breeder house, but the effectiveness is reduced dramatically because the hatching eggs are a few days old when they arrive at the hatchery. The shell surface bacteria have had plenty of time for shell penetration by this time. Some hatching egg buggy washers can be utilized for sanitizing whole buggies of eggs at a time in the hatchery. Again, the problem with this is that the sanitation does not occur early enough.

One incubator manufacturer has developed a process of hatching egg sanitation called perioxyperfusion. This process involves placing several trays of hatching eggs at the hatchery into a chamber under a strong vacuum. After the vacuum, the chamber is pressurized with ozone. Under this pressure the ozone will go inside the eggshell surface to kill microorganisms inside and outside the shell.

Mechanical washing of hatching eggs on the breeder farm deserves serious consideration by the broiler hatching egg industry now that all the disadvantages of earlier forms of egg sanitation have been addressed. Currently, 80% of the broiler chicks in the US are injected for Marek's disease in ovo and this technology has generated more interest worldwide. Improving sanitation in both the hatching eggs and the hatchery environment is critical in this situation because the eggs have been punctured and are even more susceptible to contamination.