It is well known that hygiene is critical for a succesful in-ovo vaccination process. When bacteria are contaminating the process and are injected in the egg, either into the ammnion fluid or in the embryo itself, the embryo will die very quickly, either already in the egg or in the first day(s) after hatching. 

It is therefore important to not only keep the machine and environment clean, but also to use only first grade eggs, without dirt or debris on the shell. The use of floor eggs should be avoided as it will be very difficult to prevent bacteria entering the egg during the process. 

However, some level of contamination can not always be avoided, as we are dealing with a high number of eggs and 100% control over the quality of the eggs is practically an illusion. 

To reduce the risk of bacterial contamination from the shell to the embryo, all in-ovo machines use a form of disinfection of the egg shell during the injection of the eggs, normally by spraying chloride on the top of the eggs just prior to the injection. However, the spraying of chloride just prior to injection does not give the disinfectant a lot of time to do its job. Normally it takes a while before the disinfectant effectively kills the bacteria, and when the chloride is sprayed just prior to the injection the reaction time is limited. 

It is therefore advisable to add one or two extra disinfection moments in the process of in-ovo injection. Depending on the actual situation one moment can be just after the egg trays are placed on the conveyor that brings the eggs to the injection unit, the other moment can be just before the eggs are entering the injection unit. 

So in practice it will mean that we place two disinfection units that spray either chloride or hydrogen peroxyde solution over the eggs when they pass, one just after the egg trays are placed on the belt and the other one just before the belt delivers the trays to the injection unit. If the situation doesnt allow two disinfection moments, it is good to at least install a disinfection unit just before the belt delivers the egg trays to the injection unit. On top of that, the normal spraying of the eggs by the injection unit with chloride should stay in place. 

By doing this, the disinfection system has more time to effectively reduce the bacterial load on the egg shells and with it minimize the risk of bacterial contamination of the eggs and reduction of the hatchability.