As cattle move more frequently across regions and production systems, veterinarians are increasingly tasked with helping clients prevent the introduction of infectious disease that can persist silently and erode herd performance over time. In many cases, the greatest risk is not an outbreak, but the gradual establishment of a pathogen that is difficult or impossible to eliminate once introduced.
While biosecurity includes people, equipment and environmental considerations, animal movement remains the most important driver of infectious disease risk. This was the central topic of discussion on a recent episode of Dr. Dan Thomson’s “DocTalk.”
Why Animal Movement Drives Disease Risk
“Our biggest risk is going to come from the animal itself,” said Dr. Dustin Loy, director of the Veterinary Diagnostic Center at the University of Nebraska-Lincoln. “This is going to be something that’s going to move with the animal and be transmitted from that animal to the rest of the herd.”
Transport and commingling represent peak risk periods for disease transmission. The stressors associated with hauling, dietary change and social disruption can suppress immune function and allow latent or subclinical infections to emerge. When cattle with different exposure histories mix, pathogens can spread rapidly through immunologically naive groups.
“If we can make sure that those animals we’re sourcing have a herd health program, they’ve had those calfhood vaccines and the boosters, that they have a high level of immunity to the common diseases, that’s going to really help us prevent some amount of problems,” Loy says.
However, while vaccination programs reduce risk, they are insufficient for a number of diseases of biosecurity concern. Performing diagnostic testing before animals are purchased or moved can help identify infected animals before they enter herds.
Diseases That Define Biosecurity Risk
Several diseases are consistently central to cattle biosecurity planning due to their transition dynamics, diagnostic challenges, and long-term herd impact.
Johne’s Disease
Johne’s disease remains one of the most difficult infections to control as clinical signs don’t appear until years after the animal has been infected.
“The challenge with Johne’s is that those calves are infected when they’re a month or less in age,” Loy says. “We’re not able to test those calves until they’re at least a year and a half, and usually we want to wait until they’re two or three years old just to know if they’re infected. And so that’s a real diagnostic challenge: being able to identify those animals early.”
Due to this prolonged subclinical phase, infected animals can shed Mycobacterium avium subspecies paratuberculosis, contaminating the environment and exposing young calves. Clinical signs include progressive weight loss, decreased production and chronic diarrhea, with no effective treatment. Because diagnostic sensitivity improves with age, Loy says fecal testing at pregnancy checks provides a practical surveillance point for identifying infected adults and limiting further transmission.
Anaplasmosis
Anaplasmosis is increasingly detected outside historically endemic regions, likely due to cattle movement. Caused by Anaplasma marginale, this disease is transmitted mechanically by ticks, biting flies and contaminated instruments. Calves exposed early often develop immunity with minimal clinical disease, but infection in naive cattle can cause severe anemia, abortions and sudden death.
Importantly, vectors can only transmit the organism if infected animals are present, making the testing of incoming cattle a key biosecurity step to prevent establishing a persistent reservoir within a herd.
“If we don’t have animals with anaplasmosis coming into the area, the ticks don’t transmit anaplasmosis,” Thomson says.
Bovine Viral Diarrhea (BVD)
Despite routine vaccination, BVD remains a biosecurity concern due to persistently infected (PI) animals.
“You get cows that are infected when they’re pregnant, they infect the fetus, and then the fetus does not have an immune response to the virus, so that calf is born infected. It never clears the virus and continues to shed that throughout its life,” Loy explains.
PI animals serve as powerful sources of infection, contributing to reproductive failure, immunosuppression, respiratory disease and poor performance, even in vaccinated herds. Ear-notch testing is a practical, cost-effective method for identifying PI animals prior to commingling.
Bovine Leukosis Virus (BLV)
BLV transmission occurs through blood transfer, including needles, equipment and biting insects. While many infected cattle remain asymptomatic, a subset develop lymphoma later in life, reducing longevity and productivity. Screening animals intended for long-term retention, such as breeding stock or embryo recipients, can help prevent gradual spread within expanding herds.
Core Biosecurity Questions for Veterinarians
When advising clients on cattle purchases or movements, consider asking the following questions:
- Where are the animals coming from and have they been commingled with cattle from other sources?
- Are these animals being moved between groups, pastures or regions with different disease exposure histories?
- Do the source animals have an established herd health program, including appropriate core vaccinations and boosters?
- Can diagnostic testing be used before or shortly after movement to reduce quarantine time and uncertainty?
Effective biosecurity does not eliminate all disease risk. Instead, it allows for the identification of the most consequential threats early, before they become entrenched, expensive and difficult to control.
