ReviewReview of the impact of pre-slaughter feed curfews of cattle, sheep and goats on food safety and carcase hygiene in Australia

Withholding of feed prior to transport (feed curfew) is practiced to reduce soiling during transport and optimise hide/fleece cleanliness at slaughter. However, as this represents only a portion of the time off feed before slaughter, the scope of this food safety and carcase hygiene review covers mustering-to-slaughter to enable the likely impact of the entire feed withholding period, and other related factors contributing to carcase contamination, to be evaluated. The review examines the ecology of major contaminants of carcases and whether the practice of on-farm feed curfew is likely to be effective in minimising contamination. The significance of withholding feed before slaughter is twofold. Firstly, it leads to an increase in rumen pH, due to reduced volatile fatty acids which in turn favours the multiplication and growth of undesirable enteric bacteria (Salmonella and Escherichia coli). This causes an increase in microbial hazard prevalence and counts in both rumen contents and faeces as time off feed increases. Secondly, withholding feed reduces visible contamination of the surface of the animals and facilitates hygienic dressing. Putting these points together, faecal contamination is less likely to occur if animals have been adequately fasted, but when protracted, the bacterial load is likely to be more hazardous placing great emphasis on avoiding ingesta spillage and effective between carcase hygiene measures. For pathogenic Shiga Toxin producing E. coli (STEC) that have a different ecology in livestock where feed withholding may not exert such a dramatic effect on shedding, the need to minimise hide/fleece soiling with faeces remains paramount. Consequently, the conclusion drawn is that animals should be fasted before loading only enough to allow sufficient faecal expulsion i.e. ≤24 h to maintain 'clean' livestock after transport. Adverse food borne microbial growth can be minimised by not exceeding 48 h for time off feed before slaughter.