Infectious Bronchitis infection in breeders can have a very negative influence on production, hatchability and chick quality. Often an increase of the number of poor egg shells is observed, together with discoloration of the egg shells and a loss in internal quality of the egg.
But sometimes the discoloration is not caused by IB but by contamination of the feed with coccidiostats, especially Nicarbazin. This will also cause a drop in hatchability due to an increase in early embryonic motality and is therefor sometimes mistaken for IB infection.
To distinguish between IB and Nicarbazin contamination we can take swabs for testing on virus or blood for testing on antibodies, and/or we can take feed samples or egg samples to test for the presence of Nicarbazin. This allows us to get a clear answer to the cause of the problems.
However, if we check the eggs we can already have an indication for the possible cause of the problems. IB will create discoloration of the eggs and make the eggs more variable in color, where Nicarbazin results in a number of paper-white shells where the other eggs on the trays have a normal color.
IB will also cause shell malformations, thin shelled eggs and especially sand-heads (eggs with a surface that feels like sandpaper if you rub your finger over it). Nicarbazin doesnt change the structure of the shell, only the color. So the presence of some white eggs in the egg mass without feeling rough egg shells or seeing an increase in malformed eggs shells is more likely due to Nicarbazin than to IB infection. On the other hand, Nicarbazin can cause "mottling" of the egg yolk, which is not observed with an IB infection.
Last but not least, Nicarbazin contamination gives embryonic mortality very early in the incubation process, usually at 24-48 hours (which is often recognized as poor fertility as the embryo is difficult to detect in a break out), where IB has a wider range of negative effects: fertility, embryonic mortality and chick quality are affected.