A commonly asked question is how to determine the cause of pneumonia in a clinically affected case. A reply can only be accurate if supported by laboratory investigation, as IBR can look like pasteurella pneumonia, hoose can resemble viral pneumonia and, the early case, with just a fever, could be caused by a range of diseases. So where does pneumonia start or finish? Should a farmer take a chance and hope that cases won’t arise? Or should they vaccinate against just IBR, as it is a once-off shot that might provide enough protection? We will look at some of these questions with a view to formulating a best approach to the three Cs – the cause, consequences and control – of the most common killer of nearly all ages of cattle in Ireland – respiratory disease.