Correct vaccine application is the key to better protection against infectious bronchitis, as Poultry World explains.
Vaccination against infectious bronchitis (IB) is routine throughout the UK poultry sector.
The disease, however, does continue to present significant problems due to its prevalence, its genetic diversity and the variable health status within the national flock.
The vaccines used to prevent infection and control IB are highly effective across all sectors. However, the continued presence of infection in UK flocks does raise questions about the methods used to vaccinate birds and the levels of consistency achieved in commercial production.
At a recent seminar on respiratory health, organised by MSD Animal Health, Dutch poultry specialist, Dr Sjaak de Wit from the Deventer Health Service, said one issue was the variability in vaccine uptake in the bird.
Furthermore, the vaccine may have proven efficacy, but other elements can interfere with the immune response and so the level of protection achieved. Such factors may include:
- An infection challenge by another virus not covered by the vaccine used
- Immuno-suppression in the birds due to other disease burdens
- An IB challenge occurring before the immunity fully develops
Maternally derived immunity and the response to another vaccine or disease challenge occurring around the time of IB vaccination could also influence outcomes.
Dr de Wit also believes the application method used by many producers plays an important role in determining the effectiveness of a vaccination programme.
“Using eye-drop vaccination invariably produces the best results, but as most programmes are dictated by economics and the ease of application, this is not an option for the vast majority,” he said.
Mass application methods on farm, such as spraying the birds or treatment via the drinking water, are more convenient and can be successful, but protection levels can be variable, as demonstrated by a recent Dutch trial involving 360 farms.
The studies looked at the percentage of birds which tested positive following IB vaccination using a vaccine containing the same virus. Most of the farms (95%) used on-farm spray vaccination, with 5% administering the treatment via drinking water.
The results showed that, on average, just 38% of commercial broilers and 46% of layer pullets had been successfully vaccinated and had seroconverted. In breeding flocks, 52% of broiler parents and 61% of grandparent broilers showed seroconversion.
Many variables were analysed during these trials, but the overriding conclusion was that spraying achieved the best results in smaller flocks when the ventilation was switched off, but the lights remained on. Cold water was also the best means of reconstituting a vaccine, and the second vaccination should not be administered too close to the first.
Another difficulty associated with on-farm IB vaccination is the short growing period for broilers. To address this, many integrators now choose to vaccinate at the hatchery, which enables greater standardisation and requires less labour.
“Experience shows results are usually more consistent when IB vaccine is administered in the hatchery,” said Dr Rik Koopman, global technical director for MSD Animal Health. “It also offers potential health and welfare benefits, as any reaction to vaccination is minimal at this stage in the production cycle, and there is no disturbance to the birds once they are growing on-farm.”
High quality hatchery application has been shown to produce similar results to those achieved by eye-drop application, and it is significantly better than on-farm spraying. But this level of success relies on good quality vaccination procedure, carried out by well-trained operators using well-maintained equipment.
Generally, for flocks to develop good overall IB protection, every chick must receive the correct dose of vaccine at the right time. Achieving this might require investment, but improving the quality of vaccine applications would benefit flock health, increase productivity and improve margins, said Dr Koopman.
Given the significant variation between IB viruses and the challenges presented by new and emerging strains, so-called “protectotype” vaccines have a valuable role to play.
A large number of protectotype studies have been carried out with Nobilis Ma5 and Nobilis 4-91, two vaccines that are proven to protect against a number of different IB strains.
“This protectotype concept is valuable because, instead of waiting five or six years for a strain-specific vaccine to be developed, we can use combinations of existing vaccines to achieve good levels of protection in our flocks,” said Dr Koopman.
Reduce the strain with vaccine combinations
Infectious bronchitis is genetically diverse. Caused by a coronavirus, it has many strains and can readily mutate to produce new variants.
It is one of the most significant and common diseases of poultry causing respiratory distress, sometimes kidney problems in broilers and can lead to egg quality and production problems in laying birds.
In the UK, most field viruses are found in commercial layers, and mainly in birds that are eight weeks or more beyond their last IB vaccination. Free-range layer flocks are more susceptible to disease outbreaks, but all commercial poultry is at risk, particularly when located in bird-dense areas.
The genetic variation of IB genotypes in the UK is mainly composed of 4/91 type field viruses. Other key strains include QX, which is also a field virus and the second most prevalent, and ARK, which is of vaccine origin.
Other field IB strains do exist in the UK, but at very low incidence.
Richard Currie, director of x-OvO Diagnostics, says field strains of IB can be reliably differentiated from vaccine viruses by using polymerase chain reaction (PCR) testing
“PCR is particularly useful when analysing the efficacy of IB vaccination programmes. For example, our investigations in 2012 and 2013 show 18% of broiler flocks from 304 flocks across Europe were PCR negative, in spite of having been vaccinated. This might suggest that certain application procedures are not as effective as they could be.”
PCR can also determine what viral strains exist in a flock. Having this information allows vets and producers to tailor vaccination strategies against particular strains, rather than adopting a blanket policy.
The key objective is to protect all flocks against IB through strategic and effective vaccination strategies. Achieving colonisation at farm level, by inoculating with stable vaccine strains such as 4/91, does mean field IB strains become more difficult to detect.
The best advice for producers, therefore, is to choose vaccine combinations that offer the broadest demonstrated cross protection against a variety of strains, as this minimises the threat of IB occurring in their flocks, says Dr Currie.
Producers should also be encouraged to monitor their flocks’ immune response to vaccination in order to establish that vaccinated birds are actually developing immunity to the live IB vaccine being used.