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.
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