In the third and final part of our sponsored series on infectious bronchitis, veterinary expert Sara Perez describes how she dealt with an outbreak on a Yorkshire laying unit.
The onset of an IB challenge in a broiler or layer flock can present a number of challenges to staff and vets directly involved with the farm.
From the stage at which the disease is first suspected, through to the point where a vaccine and management strategy is implemented, the focus remains on maintaining economic production.
But with access to new technologies and a growing experience in managing IB, the impact of the disease and, importantly, the time for identification, treatment and ongoing protection, are now considerably reduced.
This has been well demonstrated in the specific case of a free-range laying flock in Yorkshire.
Onset of challenge
A notable decrease in egg production, alongside a rise in daily mortality, was experienced in the 12,000 Lohmann Brown layers, between 39 and 43 weeks of age.
Farm records showed a drop in egg production – from 89% in week 39 to 80% in week 43 – while no significant change in birds’ bodyweight or egg size was reported.
Birds had received a classical vaccination programme in rear, including IBMa5, IB4/91, IB Primer and H120, but no booster IB vaccine had been dispensed in lay. The flock had also undergone a classical routine wormer treatment programme in lay, based on flubendazole in feed every eight weeks.
The deterioration in productivity motivated the farm manager to call for a veterinary investigation by the team at the Minster Veterinary Practice.
A visit to the farm could not highlight any management or technical issues, reinforcing the possibility of an infectious disease challenge.
Only a few birds looked inactive and quiet, but the symptoms exhibited at this stage were not conclusive of any particular disease, so a comprehensive investigation was necessary.
A post-mortem examination of dead and sacrificed birds highlighted the presence of mucoid tracheitis alongside fibrinous polyserositis. Most of the birds also displayed a regressed ovarian grape.
Bacteriological culture from pooled tissues with lesions recovered an abundant growth of non-typeable E coli, sensitive to most antibiotics licensed for birds in lay. Accordingly, and as an immediate response to this colibacillosis outbreak, a licensed antibiotic treatment was dispensed to birds through drinking water.
A further serological investigation from 10 birds sampled during the farm visit did not show sero-conversion to Mycoplasma gallisepticum or Mycoplasma synoviae, but highlighted abnormally high levels of antibodies against most IB variants tested for birds of that age.
It was therefore suggested that an IB challenge was likely to be the underlying condition to the colibacillosis and adjustment of vaccination against IB was therefore necessary for the next flock, as a long-term preventive approach.
It is known to be difficult to identify or distinguish specific variants of IB through traditional serology testing techniques (ELISA, Haemagglutination Inhibition), as this only detects a general antibody response to an IB viral challenge, and cross reactions between variants occur.
For that reason, and in order to decide on the most appropriate vaccination strategy to employ, a molecular investigation was necessary. Minster Veterinary Practice has an arrangement to provide samples to the specialist diagnostic and strain identification laboratory run by diagnostics company x-OvO for clients of MSD Animal Health.
The technology combines quantitative PCR (Real-Time Polymerase Chain Reaction) testing and novel RNA sequencing to give an extremely accurate identification of the IB virus.
x-OvO laboratory analysis from pooled cloacal and tracheal swabs collected at post mortem confirmed that an infectious bronchitis QX strain was present. The QX field virus characterised contained multiple differences in epitope structure and composition in relation to the QX vaccine virus licensed in some EU countries.
After discussion with the farm manager, it was decided to implement an IB vaccination programme in lay for future flocks on this site.
As the isolated QX challenge virus was different in structure to the QX vaccine virus available on the market, the efficacy of a truly individual vaccination against this field virus was unpredictable. After consideration, it was decided that a combined vaccination strategy using the broad spectrum MSD Protectotype approach would be merited.
A vaccination programme during lay using alternative applications of IB 4/91 and IB Ma5 vaccines every eight weeks was implemented in future flocks, in order to extend and broaden the cross protection generated by these vaccines.
Meanwhile, the affected flock responded well to the antibiotic treatment dispensed, and mortality decreased to normal values for age and breed within five days. Egg production came back to targeted values within two weeks and the affected flock did not experience further outbreaks.
The farm staff implemented the new in lay IB vaccination programme for the following flock of birds kept on this site. The new flock did not experience any further outbreaks and the general performance was better than the previous year.
It is important to recognise how a disease is identified and managed in a flock. This will vary in each case depending on the history of the farm, type of production and the prevalence of disease in the area. The key is in the ability to respond as promptly as possible and to work in collaboration with the supervising veterinary surgeon.
MSD Animal Health provides a range of protection strategies against IB that are tailored to each case. On this occasion we were able to establish a vaccination programme based on the Protectotype approach that provided broad protection against the particular strain isolated, and a wide range of others.
Meet the expert
Sara Perez graduated in 1998 from Barcelona University, and then completed a Master of Science at Bristol University. She joined the Minster Veterinary Practice in 2003 after five years of farm and meat hygiene work. Ms Perez holds the RCVS Certificate in Poultry Medicine and Production and became a director of the Minster Veterinary Practice in 2010. She represents the British Veterinary Poultry Association at British Veterinary Association meetings.
Working to promote healthy production
The MSD UK poultry team provides an extensive range of technical services to support vets and producers in managing respiratory challenge, including:
- On farm practical support for MSD products
- Design and establishment of vaccination programmes
- Direct access to and interpretation of x-OvO strain identification technology
- Liaison with client vets to help implement health management strategies
- National seminars with leading experts
Producers and vets who would like further information on managing IB, or copies of past editions of Respiratory Review, should contact the company on 01908 685 685. MSD Nobilis poultry vaccines and x-OvO services are provided through vets. Prescription only animal medicines should only used under veterinary direction.