Effective herd health requires package control

While vaccines can help manage disease, a biosecurity control program is essential to reduce risks and severity

Vaccines, good biosecurity and risk analysis, along with veterinary advice, together form part of a disease control package.

“You pair the vaccine with a biosecurity control program. Now you have power. If you do not do both together you will lose the game,” said veterinarian Frank Garry of Colorado State University. He spoke at the recent University of Calgary faculty of veterinary medicine beef cattle conference.

Vaccines decrease shedding of infectious agents but without other support they may not work as well as hoped against salmonella, trich-omoniasis, Johne’s disease or bovine respiratory disease.

“If you think you can vaccinate away BVD you are dead wrong,” Garry said.

Implementing a hazard analysis critical control points system can help manage and control health risks. If efforts are made to keep out scours, for example, it can also lower the risk of something like Johne’s showing up in a herd.

Vaccinations are part of a herd health plan, but they need to be used properly, said Philip Griebel, vaccine researcher at the University of Saskatchewan.

“Vaccines are a very important tool but they are only one tool in building herd health and managing disease,” he said.

“Vaccines take time to work and if you are not using them before the risk period or time of infection, you are really asking them to do things that are biologically not possible.”

The expected outcome of a vaccination program is to reduce the number of sick animals, reduce disease severity and reduce the shedding of infectious agents. It should also reduce the use of antibiotics, said Griebel.

There are a wide range of vaccines available to protect healthy animals.

A killed vaccine is an inactivated virus, bacteria, bacterial extract or purified protein. Delivery time is critical and it is important to make sure calves get the full dose for disease control.

Modified live protein or non-pathogenic virus expressed in a recombinant protein works well. However using a modified live vaccine on a highly stressed weaned calf may exacerbate sickness.

Pregnant cows can be vaccinated to fight scours and pass on that protection to newborn calves via colostrum.

However, maternal protection decreases by about 50 percent every three weeks so by the time calves are weaned, they could be in trouble.

The dams can pass on antibodies to fight bovine viral diarrhea, but in the case of infectious bovine rhinotracheitis, the youngsters are susceptible at three to six weeks of age because it appears that protection for IBR is not passed on.

Producers may have to think about vaccinating sooner because the maternal antibodies are gone.

It was previously thought using a modified live vaccine early in life was a waste of time and money because calves already had maternal antibodies.

Studies have looked at T cells needed for protection against viral infection. T cells responded better in cases where maternal antibodies were present and calves were vaccinated.

It was also thought the natural antibodies would interfere with the vaccine, but in the case of intranasal vaccines for respiratory disease, that does not appear to be the case. A single vaccination at two to six weeks of age can stimulate the immune system and reduce mortality.

Research continues to examine immunity interval. This is the time from vaccination to when the animal is protected against disease. Some may require two doses to provide immunity. As well, there are some animals that do not respond well to vaccination.

Specificity of immunity also needs more work to learn which vaccines control specific pathogenic strains.

Duration of immunity has not been studied enough. Protection may not last long so cows may have to be immunized every year.

The concept of immune memory may also exist. It is thought the immune system can mount a more rapid and specific response following re-vaccination.

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