The introduction of live vaccines for salmonella in layers in the early part of the last decade and the UK national control programme have been effective at controlling the bacteria.
But there is now evidence that cases in British eggs are on the rise, albeit in low levels.
“We can’t just blame imported eggs,” says the Animal and Plant Health Authority’s (Apha’s) salmonella consultant, Rob Davies.
We outline his advice to egg producers on management measures and cleaning strategies below.
Risk factors associated with salmonella enteritidis infection in laying hens
- Previous salmonella infection
- Absence of cleaning and disinfection
- Presence of rodents
- Induced moulting
- Larger flock size (>30,000) hens, multi-age management
- Cage housing systems
- In-line egg processing
- Rearing pullets on the floor
- Pests with access to feed prior to movement to the feed trough
- Visitors allowed in layer houses
- Trucks parking near farm air inlets
1 Get vaccine administration right
The main problems encountered with injectable vaccines are:
- Operating speed too fast
- Vaccine gun filling/calibration problems
- Wrong injection site – leakage
- Missed doses
And live vaccine issues include:
- Insufficient water tank capacity
- Inaccurate metering devices
- Failure to thirst birds
- No use of water stabiliser
- Poor/slow draining and priming of water lines
- Dirty water
- Failure to check vaccine distribution
Dr Davies advises farmers to use a combined live-killed vaccine – all Salmonella enteritidis/Salmonella typhimurium breakdowns in Britain have been in live-vaccine-only flocks.
This could be down to complacency in the administration of live vaccines, but duration of “immunity” also plays a part, as vaccines are typically licensed for 50-60 weeks, but layers are often kept for more than 80 weeks.
Work is under way to determine whether combined or additional vaccines in rear could give longer protection and if improved adjuvants or immune stimulants could be used to boost the response.
It is important for producers to avoid immunosuppressive conditions, such as poor nutrition, stress (particularly heat), intestinal or systemic disease.
2 Have a tight rodent management strategy
Vaccinations cannot get rid of salmonella if there is a rodent problem, as mice and rats recycle the infection.
Significant rodent infestations are present on almost all laying farms that are infected with salmonella. Easy external access means mice are predominantly found within houses.
In these cases, numbers are often underestimated or accepted as “normal”, and there is little checking of populations and locations.
What farmers can do to contain rodent issues:
- Don’t just rely on standard baiting points
- Be consistent in use of control methods – measures that are not properly targeted lead to bait-averse populations
- Address droppings in mini-pits by creating access for baiting beneath slats
- Bait within infested building structures
- Restrict or bait access points
- Ensure there is no spilled feed, broken eggs or dust to attract pests
Options for farmers are limited mainly to anticoagulant compounds. Even these are under threat from the Biocides Directive and new HSE requirements, says Dr Davies.
Rodents are generally resistant to first-generation anticoagulants, such as warfarin, and to some second-generation products. Bromadiolone is the most palatable choice.
Other bait options include sticky pads, wax-based blocks, edible gels, pasta- or oil-based products.
Biosecurity needs to be strict with specific dirty, changing and clean zones on farms, advises Dr Davies.
3. Put a cleaning and disinfection regime in place
Salmonella has high reistance to disinfectants, so farmers should consider what a disinfectant will be used for, and match it with a compatible detergent.
Other tips include using glutaraldehyde/formaldehyde and glutaraldehyde/QAC products for surface disinfection; choosing high-pressure power washing rather than orchard sprayers; scraping and drenching immediate external areas in 10% formaldehyde, using chlorocresol products in foot-dips and the SaniTwice technique for hands.
Mark Williams, British Egg Industry Council chief executive, says the sector is determined not to revisit the dark days of the 1980s, when egg sales fell off a cliff because of a lack of confidence in British eggs.
Version eight of the Lion Code is being updated and will go out to consultation later this year. “We want to continually educate producers and reassure them that we are on top of the situation as an industry,” he says.
The Lion training passport has courses on biosecurity, egg handling and food safety at all levels, while rodenticide handling and usage is part of Level 3 (managerial level) course.
Find out more on the Lion Training Passport website.