salmonella swine pig
Salmonella: a pig producer's perspective
Published: September 10, 2007
By: Meryl Ward - Courtesy of Nottingham University Press
Ermine Farms operates in North Lincolnshire with three breeding units and several third party grow-out units and has recently expanded into a farmshop with butchery and restaurant. A respectable start to the ZAP scoring system in 2002 for all our units deteriorated rapidly with a misjudged change to feed specifications. The situation has proved difficult to reverse, but given us invaluable experience in the ZAP scheme and different aspects of salmonella control.
Most of us are long enough in the tooth to remember the Edwina Currie episode and understand the consequences of a similar problem hitting the pig industry. The industry needs a positive outcome. We all have a duty of care to supply safe food but for a variety of reasons the ZAP programme, measured against its original objectives, has failed to date.
A recent attitude survey by BPEX reported that producers supported the principle of the programme but had many concerns over its effectiveness as a tool to support salmonella reduction. Not least because of the several millions spent to date – including producer levy money – with no discernible outcome. Compare this to the Danish scheme, started in 1995, where the annual spend has been about 2.5 million per year, and where for herds producing over 200 pigs 97% are virtually free of salmonella. The EC regulation requiring a National Control Plan and the industries own desire to position its product at a premium are key drivers to motivate the industry to do better.
The objectives were to monitor trends in levels of salmonella on individual units and achieve a 25% reduction in prevalence in the first 3 years of the programme. It should be no surprise that what in effect has been a simple ‘monitoring tool’ has not achieved solutions at an individual level to improve a complex and multifactorial problem, where different solutions are needed for different producers.
A paradox within the current scheme is that it has given a statistically reliable level of information at a national level but a poor indication of performance at individual unit level. From a producer point of view, it does not measure the level of actual salmonella at the critical control point of delivery to slaughter house, and is therefore also ineffective in providing an enforceable penalty scheme within the industry.
My aims are:
a) Address some of the concerns of the ZAP programme and why it apparently hasn’t motivated the industry to do better – we do not know that improvements are not being made as a result of some changes but the movement in the wrong direction in other quarters isn’t clouding the final conclusion.
b) Look at our own experiences.
c) Provide some practical suggestions for improvements to the current scheme.
Over the last six months, the scheme has been substantially revised as follows:
1. Early problems in the scheme relating to sample errors and statistical accuracy of results have improved with recent updates to the database. There is improved information flow with test results available on-line within 2 weeks of the pigs being slaughtered.
2. More cost-effective targeted testing has been introduced with sites below 25% positives reduced to one sample per month until a positive is found. Other sites remain at 5 samples per month. A review of sampling frequency options informed these decisions.
3. The system of three levels has been retained with the level cut-off points reduced from 85% at Level 3 and 65% at level 2 reduced to 75% and 50%. The scheme is still under review to a potential two levels. The issue with three levels is that it gives the appearance that ZAP level 1 is OK. That is fatal to the scheme. If the national average is 23% and only producers over 50% are engaged, then any improvement is likely to be negated by changes in the levels of producers in Zap level 1. Are producers who are being asked to sort the problems statistically any more of a risk (any producer who is over a 20% level is at risk of delivering active salmonella to the factory)?
4. On farm salmonella investigations and microbiological testing is available to farms in level 2 and 3 but is not compulsory.
5. A knowledge review of has been undertaken relating to the control of salmonella on-farm, which has been used to identify the main interventions suitable for onfarm use and to evaluate the feasibility of implementation as large scale field trials.
Our own experience has shown that, once established, it is difficult to reduce scores to acceptable levels. One finishing herd that had a very high score and is a strawbased scrape through system was completely depopulated and cleaned down in the summer of 2006 and the scores have already risen again to 65%.
The breeding supply unit was tested and found to be negative pre the restocking but on a retest found to be positive. The aim must be to clean up the supply farms with restraints on breeding herd supply and a new focus on testing herd supplying weaners to level 2 and 3 farms. The Danish system requires all breeding herds to be blood sampled for antibodies. If the scores exceed a certain index level, pen faecal sampling is undertaken. When the index exceeds 15, a sales ban on breeding pigs is imposed until the index falls.
Vaccination of breeding stock or weaners needs investigation but is currently not an option due to practical difficulties, but until control is achieved within breeding herds progress will be limited.
Once established on farm, a heavy burden of salmonella is difficult to reduce. Any programme to reduce levels will fail without good basic management practices including good hygiene, rodent control, all-in all out systems, management of sick pigs and improvement of the overall health of the pig. An over-use of anti-microbials will destabilise the gut flora and leave a niche that may be filled by salmonella which readily develop antimicrobial resistance. Recent BPEX trial work highlighted the ineffectiveness of many disinfectants – none were effective against salmonella typhimurium in the presence of organic matter and only two were effective in its absence. We have found that old-fashioned lime-wash is more effective especially where floors are cracked and worn.
The main culprit for transmission of the problem remains the pig. Our problem started from changes to feed specifications and we have concentrated on feed changes to find solutions. Meal-feeding, wet-feeding are not options through our bin and feeding systems. Initial changes were made to the barley levels which had some effect. The difficulty is selecting the feed or water additives that provide the most cost-effective solution.
An individual’s best options depend on the farm’s own feed and water equipment, health status of the herd and feed raw material costs. More information is required on the cost-effectiveness of different products in a UK situation. In our situation, use of an acid product through the water has proved costeffective for us and aims to provide a clean pig at point of supply to the grow-outs.
The conclusion is that there are solutions to reducing farm infection levels which can be guided and encouraged by the industry bodies. The solution for the industry needs to be whole-chain. The Danes have found that their Salmonella programme made progress in reduding salmonella at farm level in the first five years of the programme but has made little progress since.
It has become more cost-effective to take action post-farmgate e.g hot washes in the abattoir. Given the structure of the UK industry with 30% of herds outdoors and a significant proportion in straw based accommodation, the cost effectiveness of post-slaughter controls needs evaluating against the cost of farm measures.
Author: Meryl Ward
Ermine Farms Ltd, Lincolnshire
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