The presence of Mycoplasma hyopneumoniae.
A continual level of respiratory disease.
Primary or secondary infections associated with PRRS, influenza, pseudorabies and Actinobacillus pleuropneumoniae.
Heavy bacterial challenge.
The necessity for continual in-feed medication.
Variable and poor growth associated with respiratory disease.
Weaning to slaughter mortalities of more than 4%.
Finally, the cost of vaccination should be equal to or less than costs of the potential reduction in mortality and in-feed medication. Improvements in daily gain and feed efficiency become the bonus. In severely affected herds a cost benefit ratio of up to 5:1 has been achieved.
Field experiences indicate that all herds should vaccinate growing pigs from one week of age onwards.