Outbreaks in chicken flocks vaccinated against respiratory diseases could very well be the result of improper vaccination application — not vaccine failure, cautions Sjaak De Wit, DVM, PhD, at GD Animal Health Service, Deventer, the Netherlands.
Producers want the application of vaccines to be convenient, fast,
inexpensive and effective, but these are challenging goals —
especially in large flocks because vaccination is often performed
under difficult conditions that many times include hot weather,
high humidity and long hours.
To underscore his point, De Wit cites a small-scale field study conducted at the University of Utrecht, designed to assess the efficacy of vaccine application. Inexperienced veterinary students and a professional vaccination team injected 16.5-week-old birds with an inactivated vaccine. Their skill was determined by obtaining hemagglutination inhibition titers from birds.
The percentage of birds missed by the professional team was much higher than the percentage missed by students, who were nervous but tried hard to do a good job. The take-away message from the study: “Checking for quality is a good thing. It won’t cost you money; it will bring you money,” De Wit says.
IB Field Vaccination
Experiments have also shown that proper field application can be
difficult to achieve with live infectious bronchitis (IB) virus vaccines.
In a Dutch study, investigators who used an eyedropper to administer
an IB vaccine to six groups of commercial broilers achieved a
protection level of 89% to 100%. However, protection of birds from
the same six flocks that had received the same vaccine at the same
dose by spray or drinking water ranged from 0% to 86%.
“Most surprising were the differences seen on the same farm,” De Wit says.
At one farm, protection was 0% in one house and 50% in another, even though the same veterinarian vaccinated all of the birds. At another farm, birds in one house showed only 10% protection but in a second house 86% were protected. At the third farm, birds in one house showed 37% protection but in a second house the protection level was 73%.
“We concluded that there are several things going on in chicken houses that influence the efficacy of vaccination,” which prompted another field trial, he says.
In the study, investigators used an IB-vaccine spray to immunize 360 flocks — including broilers, broiler breeders, broiler grandparents and layer pullets — at around 14 days of age. Immunoglobulin M (IgM) testing indicated that only 46% were responding, a level significantly lower in broilers and pullets than in broiler grandparents, De Wit says, adding that it appears that the bigger the flock, the lower the rate of vaccine response.
“We also saw a very, very significant relationship between sampling time and IgM response,” he continues. “If sampling for IgM was conducted later, the response to the vaccine was higher. Basically, that means that there’s a lot of spreading of the vaccine through the flocks.
“The good news is that spreading compensates for birds that were missed when vaccinating, and the bad news is that if the vaccine had been applied correctly in the first place, spreading wouldn’t be needed,” De Wit adds, noting that a complete overview of the study was published in the April 2010 issue of Avian Pathology.1
House conditions affect vaccine response
A better vaccine response occurred if the ventilation system was
turned off while spraying the vaccine. However, some veterinarians don’t like to spray a vaccine with the ventilation system off because
it causes the temperature to go up, which stresses birds. In this trial,
the IgM response was 15% lower if the ventilation system was on
during vaccine application, he says.
A better vaccine response also occurred when lights in the house were on during vaccination — the response was 78% with lights on, compared to 37% if the house was dark, De Wit continues.
This fieldwork also showed that when higher temperatures of water were used to reconstitute and spray the vaccine, the IgM responses were significantly lower, he says.
Other reasons for poor vaccine efficacy can be an incorrect dosage, poor water quality if the vaccine is administered in water, the presence of another virus or interference from other vaccines, he notes.
De Wit cautions producers against making their own vaccine combinations because it could result in poor results. “It’s much better to rely on data from the vaccine manufacturers than to mix up vaccines yourself,” he says.
An increased incidence of respiratory outbreaks can also occur if something changes in the field. “Maybe the field pressure has gone up, there’s a different virus or it’s more aggressive or another variant,” he says. “But very often, if you have done some research, [you discover that] the virus has not changed and the application of the vaccines was not very good,” he says.
In the end, it’s common for a producer with more outbreaks of respiratory disease to say that the vaccine didn’t work. “But I think that, in general, it would be wise to ask if the application is really as good as you assumed it was,” De Wit says.