Bovine viral diarrhoea virus (BVDV) is one of the most economically and welfare-significant cattle pathogens globally, with persistently infected animals serving as long-term virus reservoirs and suffering unique welfare consequences.
Persistently infected cattle are born destined to experience compromised health throughout their shortened lives. Their immunotolerance to BVDV means they cannot mount an immune response to the virus continuously replicating in their tissues. They grow poorly, have reduced disease resistance, and face the eventual risk of developing mucosal disease — an inevitably fatal condition characterised by severe ulceration of the mouth, oesophagus, and intestines, causing extreme pain before death. From a welfare perspective, the identification and humane euthanasia of PI calves at birth is the most compassionate management option, preventing years of compromised health and the inevitable suffering of mucosal disease. This is simultaneously the welfare-optimal and disease-control-optimal outcome.