Step-up trials minimize risk in pullet vaccine selection

Methodical approach provides controlled monitoring of vaccine reactivity in subsets of bird population.

September 25, 2020

3 Min Read
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Michigan Allied Poultry Industries

Changing a pullet vaccination program raises concerns over whether the new vaccine can cause changes to the bird’s health and how it will affect the level of disease control. However, change can also lead to a lot of positive outcomes.

Elanco Animal Health Inc. has found that a step-up trial using a sound study design and detailed observation can help ease concerns about changing a vaccination program.

“One of the main concerns that arise when a new vaccine is being considered is whether or not it will cause significant changes to the bird’s health or the level of disease control that the poultry producer is accustomed to,” said Dr. Chase Miller, a consulting veterinarian with Elanco Animal Health. “This concern is common when a new salmonella vaccine program is under consideration, which makes a step-up trial a great way to test a new vaccine with minimal risk.”

A step-up vaccination trial is a methodical approach to testing a new vaccine by providing controlled monitoring of the vaccine reactivity in subsets of the bird population, Elanco explained.

One of the biggest benefits of a step-up vaccination trial is risk mitigation, the company said. The new bacterin is tested on missed-sex males first and then gradually tested across a company’s pullet flocks, thus instilling confidence in the new vaccination program. In addition, the step-up trial strategy provides a humane and effective approach to testing a new vaccination program in broiler breeders.

“A step-up trial also allows the poultry producer to be in the driver’s seat when it comes to deciding whether or not to adopt the new vaccination program,” Miller said. “If the trial results are not satisfactory, the company can maintain their current vaccination program or try another new one.”

Conducting a trial

When conducting a step-up trial, Miller said the first step is to set up a study comparing reactivity and mortality rates between the current vaccine and the new vaccine.

In this example, the broiler breeder team would test two salmonella bacterins on missed-sex males in one of the pullet houses.

At 18 weeks of age, the missed-sex males in the pullet house should be sorted into two groups, Miller said. One group will be vaccinated with the current salmonella bacterin, and the other group is given the new salmonella bacterin. Both vaccines would be administered in the inguinal fold of the leg, and the birds are painted two different colors for monitoring.

Fourteen days following vaccination, both groups of male birds should be euthanized humanely. The severity of the reaction in the inguinal fold should be analyzed using a standardized vaccine reaction scoring system, Miller noted. In addition to the scoring system, mortality records for both groups of male birds should be evaluated to see if any birds died before the end of the trial.

Both data sets can then be used to determine if additional trials with the new bacterin should be conducted. The next step in the trial is to vaccinate a subset of the pullet population, according to Miller.

One pullet flock should be vaccinated every week over a period of one month. Each flock should be monitored as it receives the new salmonella bacterin, and detailed records should be kept on mortality trends, feed consumption and the overall health of the flock. The monitoring should continue as the vaccinated pullets are moved into the hen house. If satisfactory results are seen, the new bacterin can be introduced or “stepped up” to the remaining flocks.

“Change can be daunting, and it can be uncomfortable,” Miller said. “The step-up trial process combines sound study design with detailed observation and helps poultry producers alleviate some of the anxiety and discomfort that comes with changing a pullet vaccination program.”

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