Comparative study on decontamination of mixed feeds by radicidation and by pelletisation

Feed components contaminated with Salmonella act as vehicles in the transmission of these bacteria to animals and hence to meat and poultry. Sanitary improvements in processing, bagging and storage do not always effectively reduce Salmonella contamination rates and therefore ingredients or mixed feed should be decontaminated at the end of processing. Enumeration of Enterobacteriaceae was used to assay the decontamination effect of pelletisation of mixed feed. A working temperature over 80° usually reduced the bacterial count by a factor of 10⁵; lower temperatures currently used, reduced it by a factor of 10³ only. In similar dose-range-finding tests on decontamination with ⁶⁰Co gamma rays, about 0.5 Mrad were required for reductions in the counts of the most resistant Enterobacteriaceae by a factor of 10⁵. Survival curves being usually non-linear, ‘gross effective dose’ had to be used as a parameter. Neither loss of nutritive value nor the occurrence of orally toxic factors was observed when rats were fed for 2 years on a ration containing 35% fishmeal irradiated at 0.8 Mrad. A combination of improved sanitation, pelletising at the highest possible temperature and, if still required, terminal low-dose irradiation of the hermetically bagged material seems, therefore, a promising approach to the manufacture of Salmonella-free feeds.