Vaccination

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So you’ve vaccinated your cows and calves but still have disease problems— abortions, scouring calves, respiratory disease at weaning or in the feedyard. The vaccine labels claim they protect against these diseases, so what is going on?

For frustrated producers dealing with death loss and escalating veterinary expenses, it can be easy to point fingers at the vaccines. The truth behind these outbreaks actually is more complicated, but one thing is clear. Licensed vaccines, used properly, are effective in protecting cattle from disease. We can be confident in this, because companies must prove the efficacy of their vaccines through an exhaustive and expensive research process before they can bring them to market.

Proving they work
“There really are not any bad vaccines on the market,” says veterinarian Jim Rhoades, who manages technical services for Novartis Animal Health. The licensing process is designed, by law, to assure that vaccines are safe, potent, effective and accurately labeled before they reach the market, he explains.

The Center for Veterinary Biologics, a branch of USDA’s Animal and Plant Health Inspection Service, regulates these products and oversees the licensing process. APHIS scientists carefully review the methods and results of laboratory tests, field trials and manufacturing.

“It’s a very rigorous process that takes an average of about five years,” says veterinarian Kent McClure, general counsel for the Animal Health Institute. Product development begins when a company recognizes a need for a vaccine to address a specific pathogen. Then the manufacturer must isolate the pathogen and conduct laboratory research on how to develop either a killed or modified-live vaccine based on that pathogen.

Once the company creates a vaccine it considers a candidate for commercial release, it develops a “master seed,” which is a pure culture of the pathogen used to assure consistency in production of the vaccine. Dr. McClure likens this to a “starter” for making sourdough bread, in which the same population of yeast is propagated for repeated use. Extensive laboratory testing by the company and by USDA confirms the purity of these cultures.

Next, the company tests the product on limited numbers of animals in a controlled setting to assure there are no negative reactions. From there, the company moves to “challenge studies” in which scientists expose vaccinated animals and control groups to the target pathogen to determine whether the product offers protection against the disease.

If the vaccine still appears promising at this point, the company conducts large-scale field trials, typically in at least three different areas of the country. These trials evaluate the product’s efficacy in real-world production environments. At each of these stages, the company must submit its data analysis to USDA for review.

Finally, the company must prove it can produce a consistently pure product by creating, from scratch, three separate batches of the vaccine for extensive analysis by USDA scientists. The agency also inspects the manufacturing facility and evaluates personnel to assure their production and quality-assurance capabilities. Even after the vaccine is licensed, the company must test every batch and submit analysis, and samples of the batch, to USDA for review. Dr. Rhoades adds that upgrading an existing vaccine to add a new label claim, such as coverage for an additional BVD strain, also requires several years of research.

You need all three
So with all of these safeguards in place, how is it that viral diseases sometimes break out in vaccinated herds? The answer, Dr. Rhoades says, is that vaccines cannot work alone. “I think of a herd-health program as a three-legged stool,” he says. “Vaccines are one leg, nutrition is another, and the third leg is management. Take away either leg, and the system fails.”

Whether on pasture or in a feedyard, good nutrition in-cluding mineral supplements is critical for an animal to maintain its immune system, Dr. Rhoades says. The management leg includes producer-controlled factors including genetic selection, good facilities, low-stress handling, comfortable environmental conditions and biosecurity to limit exposure to pathogens.

In a research environment, scientists design vaccine trials in ways that control other variables to produce valid results, Dr. Rhoades explains. In other words, treatment groups differ in whether or not they receive the vaccine, and perhaps in timing or dosage. Otherwise, researchers try to keep environmental conditions, diet and rate of exposure to pathogens the same. They randomly select and sort cattle into groups to account for genetic differences. They make these efforts so that when they find differences between treatment groups, they can attribute the difference to the treatment—the vaccine.

In a production environment, those controls sometimes break down. One producer might use a vaccine with excellent results, while his neighbor, using the same product, fights an outbreak of viral disease in his herd. A closer look at the diseased herd probably would reveal some combination of factors—poor nutrition, stress, high levels of exposure—that com-promised the animals’ ability to resist the pathogens.

Finally, there is the issue of proper administration of vaccines. If the label specifies one dose, it means research has shown that one dose of the product is effective. If the label specifies two doses, research has shown that two doses provide efficacy; one dose does not.

Label instructions for timing of administration are also based on science, Dr. Rhoades says. Cows, for example, begin producing colo-strum about six weeks before calving. Vaccines intended to protect the calf against scours, administered two to four weeks prior to that time, help the cow produce the necessary antibodies for passive immunity. The same vaccine administered a week before calving will not be effective.

In the case of BVD, the virus can pass to the fetus at 40 to 120 days gestation, Dr. Rhoades says. For a vaccine to provide fetal protection, the producer must administer it before that time. “If the label says to use a vaccine prior to breeding, it’s because that’s when research shows that it works,” he says.

Dr. Rhoades encourages producers to work with their veterinarians to implement a complete herd-health program. Select appropriate vaccines based on your location and production system, while also concentrating on the other two legs of the stool—nutrition and management.



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