What is herd disease?

There is no specific syndrome or infection called "herd disease", so this is a general term meaning "a disease affecting a population of animals". In this context, a herd disease is any disease affecting a herd, which in the United States is generally a collection of ruminants, of which the only domestic species is cattle.

Examples of herd diseases include Moraxella bovis, the bacteria responsible for pink eye or conjunctivitis and primarily affects white-faced cattle like Herefords and baldies; bovine viral diarrhea virus (BVDV), which is perpetuated in the herd through persistently infected (PI) shedders infected in utero; and Mycobacterium avium paratuberculosis, the causative agent of Johne's disease and perpetuated in the herd through chronic shedders infecting calves at birth.