With the introduction of the United Kingdom Zoonoses Action Plan (ZAP) for salmonella in pigs in July this year, thoughts are being directed as to how this infection can be reduced in piggeries and how ZAP will impact normal farm management routines. One proven method of control is through the acidification of wet and dry feed below pH 4.5, even to 3.5, which capitalizes on salmonella species lack of acid tolerance. Acidification is achieved through the use of additives or the natural fermentation process of liquid feeds. Pharmaceutical companies now need to consider the effects of acidification of feeds on their antimicrobial products, which may be incorporated in them.

From slaughter house surveys, it has been shown that 23% of the UK pig herd carries salmonella in their intestines and that 5% of carcasses are contaminated (8% of sausages), so ZAP has been introduced to reduce the possible contamination of pigs and pig meat and the concomitant risk of transmission to man. The Public Health Laboratory Service linked 16.5% of meat related salmonella incidents in man to pig meat products, although after removing other causes, such as poor storage, cross-contamination from other meats and salmonella infected meat handlers, the likely percentage will be significantly lower, closer to 4%.

Salmonella often infects the younger growing pig, and its carriage and excretion is usually lower by slaughter age but seroconversion remains quite high. The test at the slaughterhouse will be based on the meat-juice Elisa test, which is not meant to be as sensitive as serological (blood) tests but the weakness of the test is that it may not reflect the actual level of infection in the pigs at slaughter but will reflect the challenge they have experienced previously. It is also a non-specific test for salmonella species.

Graph 1. Salmonella infection and seroconversion in three Danish pig herds

(Kranker and others, 2002)

If salmonella is cultured and identified on a farm it is useful to carry out a sensitivity test to see which antimicrobial may be effective. The majority of pig salmonellae are S. enterica Typhimurium (67%), which are unfortunately more resistant than others and tend to be invasive into the body (systemic) rather than just colonizing the gut.

Table 1. Pig salmonella antimicrobial sensitivity (%)

A number of vets, nutritionists and farmers have enquired whether in-feed antimicrobials are stable in acidified or fermented feed conditions and Novartis Animal Health have looked into this to help their customers. Most compounds are salts with weak bases and strong acids like hydrochloric acid (HCl) and are acidic in solution and are stable.

Table 2. Likely stability of antimicrobials products in acidified conditions

Products that are salts with strong bases such as potassium and sodium and weak acids are usually less stable in acid conditions e.g. potassium penicillin V, although more acid stable than penicillin G. Potencil should not be included in fermented liquid feed although it may be included in a dry acidified feed. Sulphadiazine sodium is alkaline in solution but is still relatively stable in acid conditions.

Clearly the introduction of the ZAP salmonella scheme for pigs is expected to result in some major changes to pig management and feeding over the next 12 months, so make sure it does not adversely affect your medication programs.

 

References:
Kranker, S., Alban, L., Boes, J. and Dahl, J. (2002) Longitudinal investigation of Salmonella Typhimurium in integrated swine herds. Proceedings of the 17th International Pig Veterinary Society Congress Ames, Iowa, USA, 1, p317.

VLA/DEFRA (2002) "Salmonella in livestock production" Veterinary Laboratories Agency, Addlestone, UK, p145.

 

More on Pig Diseases & Medication:  Octagon Technical Papers

~  www.octagon-services.co.uk  ~