IB is a very well known disease in our poultry world, both in broilers and egg producing birds. In breeders and layers it results in problems with production, shell quality, fertility/hatchability and day old chick quality. Although in egg producing birds it does not result in high losses, the impact on production can be very costly. A strict bio-security protocol and adequate, tailor made vaccination program are essential for controlling the disease.

When the disease attacks birds at a very young age (typically in the first week of life) it can also result in so-called false layers in production. The virus at that very young age damages the oviduct which prevents the organ from normal functioning when the birds come in production. A typical sign for these false layers is an accumulation of fluid in the oviduct. At this moment we think that there are perhaps also "milder" forms of false layers, that are not characterized by a massive amount of fluid in the oviduct but might as well give problems with production and fertility.

To prevent the disease from creating that damage at such a young age it is important to vaccinate breeders and layers at the hatchery or directly on arrival at the farm. However, not all the IB strains are equally resulting in false layers. The Massachusetts type strains are much less related to false layers than strains like QX or 4/91. This means that if there are false layer type problems observed in breeders or layers in production, we might consider to add a 4/91 type strain in the vaccination program, either at the hatchery or on arrival as day old chick at the farm. Because of the relatively low cost of the vaccine and the huge economical risk if some birds will develop "false layer" type of lesions, it might be a consideration to include 4/91 in the day old vaccination schedule (hatchery or farm) even if no obvious signs in production has been observed in previous flocks. Once the damage occurs, it cannot be repaired anymore.