Biosecurity in Livestock Herds 

By Larry Schuler, North Dakota State Veterinarian, Bismarck

The term "Biosecurity" conjures up ideas of men clad in white suits with respirators and biohazard signs posted everywhere. Simply put, however, biosecurity simply means a set of management practices that prevent infectious diseases from being carried into a herd.

New strains of infectious agents are emerging, such as BVD type II and Salmonella typhimurium DT 104. New diseases such as hairy heal wart and Neospora sp. have emerged and are spreading across the country. Old diseases, such as Johnes disease and leukosis, are increasing in importance as we learn more about them and begin to understand their effects on productivity. These disease concerns, along with global trade, food safety concerns and the development of antibiotic resistance are increasing the pressures on producers and veterinarians to institute biosecurity measures that will prevent the introduction of a disease into a herd.

When we think about disease prevention in a herd we frequently think about vaccination of the herd for the diseases about which we are concerned. But a vaccination program alone will not completely protect a herd from all of the diseases that may have an economic impact on a herd. Also, vaccination programs are generally applied and are not tailored to the risks of the specific operation.

There are four general areas to pay attention to when instituting a biosecurity program for a herd. They are isolation or quarantine, testing, vaccination, and sanitation.

Quarantine of incoming cattle is one management practice that may decrease the likelihood of introducing certain diseases to the herd. Quarantine of incoming cattle means keeping them separate from the established herd. The quarantine area should be set up so new arrivals will not share the same air space, food or water with the established herd.

Quarantine is effective for preventing diseases with short incubation periods and with no carrier states such as bovine respiratory syncytial virus (BRSV) and bovine viral diarrhea (BVD) in nonpersistently infected animals. Generally, a quarantine period of three weeks will allow any of these diseases that may be incubating to be expressed before the new animals would be introduced into the established herd.

For diseases, such as Mycobacterium paratuberculosis (Johnes disease), brucellosis, leptospirosis, neosporosis, and leukosis, quarantine is not an effective biosecurity measure because of the inapparent carrier state in which animals appear normal but can still carry and potentially shed the organism. In these instances, the inapparent carrier state will not be detected during the quarantine period unless the animals are tested.

Testing of imported cattle can be useful in decreasing the risk of introducing disease into a herd. Tests should be evaluated to ensure that they will achieve the desired goal of decreasing the risk of disease entry into your herd. We need to remember that disease testing is not 100% and the sensitivity of the test should be considered when testing potential animals for addition to your herd.

An alternative to individual testing of imported cattle may be testing of the source herd and importing animals only from disease-free herds. Another alternative is to purchase from herds that are participating in herd disease certification programs, such as a Voluntary Johnes disease Herd Status Program that is being developed for use in North Dakota.

Vaccination of the resident herd and imported animals is another way to manage risk of mixing cattle of different disease statuses. Vaccination is the most common way veterinarians and producers have attempted to solve biosecurity risks. The effectiveness of vaccines, however, is limited and vaccination should not be looked at as the only or even the primary means of decreasing risk of disease. Even under optimal conditions, not all cattle will respond to vaccination nor will all that respond to vaccination be protected from infection.

Livestock producers may vaccinate the established herd to increase the immunity to pathogens that may be introduced by imported cattle or may require vaccination of imported cattle prior to entry into the herd to decrease the introduction of disease agents.

Sanitation involves protecting herds from exposure to infectious agents. Sanitation practices may involve requiring all visitors- including veterinarians, milk inspectors, AI techs, and other service personnel- to wear clean boots and coveralls. A footbath and brush for visitors should be provided for them to disinfect their boots.

Other sanitation steps that should be considered are preventing dogs, cats, birds, rodents and wildlife access to feed supplies. Fecal contamination of feed supplies may provide for the transmission of various organisms, including Neospora caninum and Salmonella spp. Fecal contamination of feed supplies may also occur by using manure handling equipment to feed cattle. Feeding heifers with equipment used for handling manure may increase the risk of infection with Mycobacterium paratuberculosis (Johnes disease) as well as salmonellosis by increasing fecal contamination of feedstuffs. The prevention of fecal contamination of feedstuffs may be important in minimizing the prevalence of pathogens known to affect humans such as E. coli 0157:H7 and Salmonella spp.

Biosecurity measures need to be carefully considered and discussed with your veterinarian. It is true that most diseases are bought and paid for. On the other hand the cost effectiveness of the biosecurity measures that are instituted need to be considered. The risk of introducing disease, cost of the disease once it is introduced into a herd, the cost of the biosecurity measures and the amount of risk that producers are willing to live with will determine the biosecurity measures that each livestock producer will set for their operations. As time goes on biosecurity will likely become more important as food safety and quality, international trade concerns, and efficient production pressures increase.

One last word of advice, the most dangerous animal to bring into a herd is the young salebarn calf that is brought in to replace calves that have died. When it comes to these, "Just say No".

Dr. Larry Schuler
North Dakota State Veterinarian
Dept. 602
600 E. Boulevard Ave.
Bismarck, ND 58505-0020

NDSU Central Grasslands Research Extension Center

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