Bovine respiratory disease

Bovine respiratory disease (BRD) is the most common and economically devastating infectious disease affecting beef cattle in the world. It is a complex, bacterial or viral infection that causes pneumonia in calves which can be fatal. It also affects many other species of feedlot animals like sheep and pigs, but is most prominent in calves. The infection is usually a sum of three codependent factors: stress, an underlying viral infection, and a new bacterial infection. The diagnosis of the disease is complex since there are multiple possible causes and cattle are reluctant to display any indications of pain.

The disease manifests itself most often in calves within four weeks of weaning, when calves are sorted into groups of roughly 10–15 in number, and sold to different feedlots via train, tractor trailer, and truck. Because of this, BRD is most commonly referred to as "shipping fever". It is not known whether the stress itself, co-mingling, or travel conditions are at most to blame, and while studies have identified general stressing factors like transport and cold weather conditions, there is still no conclusive evidence on more specific factors (e.g. distance, transport mode, temperature, or temperature volatility).