It is principally of viral origin and the following viruses have been implemented in disease. [[Bovine Respiratory Syncytial Virus|Bovine respiratory syncytial virus (BRSV)]], [[Bovine Parainfluenza - 3|Parainfluenza- 3 (PI3)]], [[Bovine Viral Diarrhoea Virus|Bovine viral diarrhoea virus (BVDV)]], [[Bovine Adenovirus|Adenoviruses]], [[Bovine Coronavirus|Calf coronavirus]] and [[Infectious Bovine Rhinotracheitis|Bovine herpes viruses]]. | It is principally of viral origin and the following viruses have been implemented in disease. [[Bovine Respiratory Syncytial Virus|Bovine respiratory syncytial virus (BRSV)]], [[Bovine Parainfluenza - 3|Parainfluenza- 3 (PI3)]], [[Bovine Viral Diarrhoea Virus|Bovine viral diarrhoea virus (BVDV)]], [[Bovine Adenovirus|Adenoviruses]], [[Bovine Coronavirus|Calf coronavirus]] and [[Infectious Bovine Rhinotracheitis|Bovine herpes viruses]]. |