BVD, or Bovine Viral Diarrhea, is a viral infection that affects cattle. It is caused by the Bovine Viral Diarrhea Virus (BVDV), which can lead to various health issues in infected animals, including respiratory problems, reproductive failures, and gastrointestinal disorders. The virus can be transmitted through direct contact with infected animals or contaminated environments. There are two main forms of BVD: the acute form, which causes sudden illness, and the persistent form, where animals carry the virus without showing symptoms. Control measures include vaccination and biosecurity practices to prevent the spread of the virus within herds.