Animals and Salmonella

Before you ask, Brexit is highly unlikely to have any tangible effect on the UK’s approach to Salmonella control in laying hens.  As with other aspects of farming, increasingly retailer requirements supersede the minimum standards stipulated by law and as such Salmonella surveillance and control is likely to be mandatory whether due to legal statute or retailer requirement.  Similarly the Lion code lays down requirements for Salmonella surveillance and control which exceed those minimum standards required by law. 

 

So why are chickens and turkeys singled out?

The cost of running a national control programme is significant both to the individual producer and the state.  Prior to control programmes being implemented there has to be sufficient evidence that cases of Salmonella can be controlled and the overall target of a reduction in the number of infected flocks can be achieved.  All of this needs to be offset against the cost of cases of Salmonella to the country (ie if we find Salmonella in a flock are we able to effectively control it and if so are the costs of surveillance and monitoring less than the costs (both monetary and social) of treating Salmonella in the human  population.

 

The poultry industry is highly integrated and consolidated.  We have a good understanding of biosecurity, we have a reasonably well developed armoury of Salmonella vaccines and we produce poultry meat and eggs from large holding which can become widely disseminated throughout the supply chain.  If a large layer holding becomes infected with Salmonella it can lead to a very complicated food poisoning outbreak in the public.  If a layer-breeding holding becomes infected with Salmonella a significant number of hatching eggs could be infected leading to wide scale infection of replacement layers either due to direct infection of the egg or cross-infection in the hatchery.  Likewise the highly efficient and mechanised methods of slaughter employed in poultry processing plants can mean that a single infected bird can contaminate a large number of other birds processed on the same day.

 

On weighing up these factors the EU has determined that control of Salmonella in chickens and turkeys offers a cost benefit to the public and thus we are obliged to conduct regular testing of our flocks for Salmonella with significant consequences if a Salmonella enteritidis or typhimurium are detected.  There is no such requirement in other livestock species and no legal mechanism to prevent infected meat entering the food chain when it originates from other species.

 

Crucially, amount Salmonella in the national herd of a farmed species does not necessarily correlate with the number of cases of food poisoning in humans.  Infections of meat producing animals (who generally live much longer than meat chickens) have often resolved by slaughter age.  The slaughter process for non-poultry species is generally much less likely to result in cross contamination between individuals and, for pork in particular post slaughter processing (in the production of bacon for example) infers anti-microbial properties.

 

So, in summary the poultry industry enjoys the dubious honour of having a National Control Programme for Salmonella whilst other food producing animals do not.  And whilst we suffer the costs of testing and the consequences if Salmonella is detected, we also enjoy a reputation for producing safe, healthy and inexpensive food.

 

But if the government is not concerned about Salmonella in other species why should I be concerned?

Precisely because Salmonella infection in laying hens may have significant consequences, it is vital that producers are aware of all potential sources of infection.  In recent years laying flocks have become infected with Salmonella strains which have been linked with pigs, cattle and sheep.

 

In 2017 and 2018 two food poisoning outbreaks occurred which were associated with Salmonella typhimurium in sheep.  Given that sheep often co-graze with laying hens producers are urged to conduct their own risk assessment on this activity.

 

Similarly, cattle often co-graze with sheep and are another species where Salmonella typhimurium can be found.  Phage type 104 in particular seems to have increased in prevalence in recent years and has been responsible for infections in laying flocks which co-graze with cattle.

 

Co-grazing is not without risk, however these risks can be controlled to a certain extent.  Voluntary testing of sheep and cattle should be conducted to assure yourself that they are free of Salmonella infection.  Assuming your co-grazers are clean, efforts should focus on maintaining a disease free flock/herd by minimising stock movements and ensuring all bought in animals are also “clean”.  You may wish to consider vaccination in cattle and as always other risk factors for example rodent control is vital.

 

Unlike sheep and cattle, pigs present a rather different risk to free range laying flocks.  The prevalence of Salmonella in pigs is very high.  Salmonella typhimurium and monophasic typhimurium appear to be readily isolated from environments where pigs have been farmed.  Salmonella typhimurium can be found in puddles, flies, wild birds, rodents dust and hedgerows around commercial pig units and this represents a significant source of infection for laying flocks where infection may result in slaughter of the laying flock.  Protecting your flock from Salmonella infection depends on very high standards of biosecurity, excellent rodent control and management of feed bins and ranges to minimise the number of wild birds on the range however where pig units are located in close proximity to your laying units it is recommended that additional advice is sought to explore whether additional control measures may be indicated.  You may wish to enhance the Salmonella vaccinations for future flocks or engage with the pig enterprise to see whether they are able to locate mobile herds as far away as possible from the chicken house.  Particular attention should be paid to vehicles visiting your site, particularly if roads around the farm are obviously contaminated with pig muck.  A Salmonella vaccine for pigs has recently been developed and it is hoped that this will be used as part of an increasing desire to control Salmonella, however, in the meantime farmed species which are not regulated by a Salmonella control program ought to be viewed with some suspicion and where these farming enterprises are in close proximity to your laying unit a specific risk assessment ought to be conducted.