Muscle tissue of healthy animals is considered essentially sterile, with the exception of lymph nodes (Romans et al., 1994). However, all meat-producing animals harbour large numbers of various microorganisms on their surfaces exposed to the environment, i.e., skin/fleece, hooves, and mucosal membranes of the digestory and respiratory tracts, with relatively high microbial concentrations of 106cfu/cm2 skin or g faeces, respectively. Pathogenic bacteria excreted in stables may be ingested orally and so reinfection of animals may occur, namely the colonisation of the guts of very young animals with immature gut flora. Use of contaminated feedstuff has been addressed as an important factor, transportation of the animal, insufficient disinfection of transportation vehicles and extended lairage time at the slaughterhouse allow excretion of pathogenic bacteria, and psychogenic stress may release microbes arrested in hepatic mesenteric lymph nodes. Both factors have been addressed as a source of cross-infections (Smulders, 1995).
Removing the bacterial load from the outer as well as the mucosal surfaces of the live animal would be a promising idea. To date, showering of pigs is a successful technique (Smulders, 1995), as well as the 'clean livestock (cattle) policy'. James et al. (1997) briefly review trials in pre-slaughter cleaning of animals and Huffmann (2002) concisely reviews pre-harvest experiments (composition of the diet, competitive exclusion cultures, drinking-water treatment, immunisation) with special regard to the reduction of E. coli 0157.
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