Final answer:
The most likely source of bovine viral diarrhea in a herd of cattle is persistently infected animals. They can spread the virus continuously within the herd through bodily fluids and excretions.
Step-by-step explanation:
The most likely source of bovine viral diarrhea (BVD) in a herd of cattle is C. Persistently infected animals. BVD is primarily spread through direct contact with these animals that carry the virus for their entire lives, shedding it in their bodily fluids and excretions.
The presence of these animals can perpetuate the spread of the virus throughout the herd. Other potential sources of infection, such as wildlife, contaminated feed, or contaminated water, are less likely but not impossible channels for the disease.
The most likely source of bovine viral diarrhea in a herd of cattle is persistently infected animals. Bovine viral diarrhea is a viral disease that can be transmitted from one animal to another, and persistently infected animals are carriers of the virus.
These animals shed the virus in their bodily fluids, such as saliva and urine, and can spread it to other members of the herd through direct contact or contaminated surfaces.
Therefore answer is C. Persistently infected animals.