Food Safety: Addressing Salmonella and antimicrobial usage in the poultry industry

By Paul McMullin MVB DPMP MRCVS - This article presented at WVPA Denver looks at a number of food safety issues concerning the poultry industry including topics such as Salmonella, Campylobacter, antibiotic resistance and animal welfare.
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Food Safety, Addressing Salmonella and antimicrobial usage - By Paul McMullin MVB DPMP MRCVS - This article presented at WVPA Denver looks at a number of food safety issues concerning the poultry industry including topics such as Salmonella, Campylobacter, antibiotic resistance and animal welfare

The market for poultry products is still growing substantially in many countries, and is highly competitive. There has, however, also been a steady rise in regulation and increasing customer requirements with respect to a broad range of issues affecting the way poultry are produced. These include environmental impact, Salmonella infection, in particular S.enteritidis, Campylobacter infection, reduced availability of therapeutic antimicrobials and anti-protozoals, restrictions on use of antimicrobial growth promoters, restrictions on the use of animal proteins and genetically modified materials in feeds, consumer concerns for animal welfare and increased demand for products from alternative production systems. These issues have already had an impact in many countries and are likely to continue to do so, though variably between countries according to local market conditions, trade, politics etc. This is happening against the background of continuing progress in genetics, disease control and nutrition, to which the industry has long been used to adapting.

These issues are often dealt with both by industry and regulators on a piece-meal basis and in some cases such action has produced remarkably positive results. For the United Kingdom perhaps the best example is the dramatic reduction of Salmonellae in general and, in particular S.enteritidis, in both meat poultry and the egg production industry. Given that this is clearly a success story, a review of the history of the relevant pathogen control programmes can provide us with some insights which may be applicable to some of the other issues we are currently dealing with. In the first place it must be recognised that Salmonella enteritidis had spread very effectively within both the meat and egg poultry industries in many countries, in particular in the 1980’s. It was some time before we fully appreciated the extent of its ability to transmit between poultry generations and contaminate, and sometimes grow in, egg contents. It was the public declaration by a junior health Minister in the UK in late 1988 that “all eggs …. were from Salmonella infected flocks” which generated a collapse in the egg market and subsequently a series of activities, even though the statement was not accurate(3). What was undeniable was that the number of human cases of Salmonella enteritidis infection had risen from about 3000/year to 17000/year over a ten year period. Most of the rise was due to phage type 4. Intense regulatory activity ensued. Compulsory microbiological testing of breeding and laying flocks was instituted, with slaughter of infected flocks with compensation. Much basic research work on the epidemiology of Salmonella infections was initiated. However the relatively severe consequences of isolating the organism actually discouraged testing over and above the minimum required by the legislation. Serological testing (4,8) was widely used as a surrogate for microbiology in trying to understand the epidemiology. The breeding industry identified problem farms and improved disinfection and biosecurity but breaks still occurred.

In 1993 the testing regime for commercial layers was relaxed, and compulsory slaughter ceased, because of failure to agree a uniform testing regime around Europe. Vaccination of broiler parents with a commercial S.e. bacterin started in 1994 and steadily increased in use year-on-year(3). Coincidentally the number of breeder cases soon began to show a decline. This is likely to have been the result of several factors, in addition to vaccination. The results of basic research were, for instance, being published and applied in practice. Progress in reducing Salmonella contamination in commercial eggs had been relatively slow however. In 1998 the main industry organisation dealing with layers launched a new assurance scheme, the “Lion Code” whose primary objective was to improve the food safety of eggs and reverse the adverse publicity the industry had suffered. A key component of this scheme was that all laying pullets should be vaccinated against Salmonella enteritidis. The effects of this scheme are now very evident. Its importance was further confirmed when there was a series of egg-associated outbreaks of Salmonella infection in Autumn 2002 which turned out to be associated with imported eggs. Antibiotic resistance also comes into “the Salmonella story”. For almost 30 years the UK has been monitoring Salmonella isolates from food animals for antibiotic resistance. Serotypes come and go and resistance profiles largely come and go with them. S.typhimurium DT104 has, because of its highly resistant profile, and tendency to infect different farmed species, been a significant concern but is only occasionally isolated in poultry.

The use of antimicrobials in poultry production has been reviewed elsewhere (5,6,7). The risk of transferable antibiotic resistance reducing treatment options in human medicine has been the justification given for an active campaign against antibiotic growth promoters in Europe. Scandinavian countries have very effectively influenced politicians and regulators to the point that the European Commission has indicated that such products will be withdrawn by 2006. There remain a number of problems relating to this political decision. Until such point that the evidence that such use poses a significant risk to human health it seems very unlikely that the European Commission will be able to insist on this approach for imported meat. There are indications that, at least under certain circumstances, withdrawal of growth promoters and reduction in the range available is increasing the need to treat with therapeutic antimicrobials. Most of this usage is related to the treatment of intestinal disease in broilers, which, if untreated can cause significant welfare problems through the occurrence of wet litter, especially in temperate climates.

Many of the issues we are dealing with in this context involve assessment and communication of risk to the poultry industry, its customers and the general public (1). European regulators are functioning in a market environment of surplus food supply, and a political environment requiring a pro-active, open approach to all matters of food safety. The “Precautionary Principle” is seen by some as the panacea for all such problems (2), however the above examples clearly illustrate the need to include an assessment of the risk associated with the precaution.

Poultry Welfare is also a growing issue in a number of countries. This often focuses on specific issues such as use of cages for layers, stocking densities, and beak trimming. However practical welfare goes far beyond these issues. As managers and advisers our role is to provide an environment (in the broadest sense, physical, social, microbiological) that the particular genetic stock we are using is adequately adapted to, thus minimising the need for physiological adaptation through the stress reaction. The various other issues discussed here makes this an increasingly challenging task because they can interact with nutrition, disease status, economics and management. However even if dealing with these challenges is not a legal requirement there is every possibility that the market will require that we are proactive. Keeping up with these diverse and evolving poultry health and welfare challenges will require research, collaboration and innovation. These have always been the strengths of the poultry industry.


1. Ahl A.S. and Buntain (1997). Risk and the food safety chain: animal health, public health and the environment. Rev. Sci. tech. Off. int. Epiz., 16 (1), 322-330.
2. Belveze, H. (1998) Guidelines on the application of the precautionary principle. European Commission DG XXIV Consumer Policy and Consumer Health Protection 17th October 1998
3. Gooderham, K. (1997) Biosecurity and vaccination in eradicating Salmonella enteritidis
4. McMullin, P.F, K. R. Gooderham and G. Hayes (1997) A commercial Salmonella enteritidis ELISA test: Results arising from its use in monitoring for infection and response to inactivated vaccine. World Veterinary Poultry Association Congress, Budapest. Abstract in Proceedings
5. McMullin, P.F. (1999) Prudent Use of Antimicrobials in Animals: A Poultry Specialist’s View* OIE European Meeting on Prudent use of Antimicrobials in Animals. Paris 25/3/99
6. McMullin, P.F. (1998a) Quinolone usage in poultry medication in Europe. Use of Quinolones in Food Animals and Potential Impact on Human Health World Health Organization, Geneva, Switzerland. 2-5 June 1998.In Proceedings pp 123-132
7. McMullin, P.F. (2001) Antimicrobial Use and Antimicrobial Resistance, Proceedings of the North Easter Conference on Avian Diseases, College Park, Maryland USA
8. Nicholas, R.A. and Cullen, G.A. (1991) Development and application of an ELISA for detecting antibodies to Salmonella enteritidis in chicken flocks. Vet.Rec. 128:74-76

Source: Presented at WVPA Denver - August 2003

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