The effect of temperature on the growth and persistence of Salmonella in fermented liquid pig feed

Two studies were conducted to investigate the effect of temperature on the fate of Salmonella enterica subsp. enterica serovar typhimurium DT104:30 in fermented liquid pig feed. These were (1) by co-inoculation of feed with S. typhimurium DT104:30 and Pediococcus pentosaceus, as the fermenting organism, and (2) by fermenting feed for 48, 72 or 96 h prior to inoculation with S. typhimurium DT104:30. In co-inoculated feed incubated at 20 °C, S. typhimurium DT104:30 persisted for at least 72 h. In contrast, in feed incubated at 30 °C, no S. typhimurium DT104:30 were detectable 48 h after inoculation. In pre-fermented feed, S. typhimurium DT104:30 died four to five times faster in feed maintained at 30 °C (Dvalue 34–45 min) compared with feed maintained at 20 °C (Dvalue 137–250 min). This was not entirely due to differences in lactic acid concentration as feed fermented for 72 or 96 h at 20 °C and feed fermented for 48 h at 30 °C contained similar concentrations of lactic acid (160–170 mM). Low numbers of S. typhimurium DT104:30 were still detectable in fermented feed 24 h after inoculation at 20 °C. In contrast, none were detectable 6–7 h after inoculation at 30 °C. The results of these studies indicate that it would be advisable for pig producers to control the temperature of liquid feed tanks to reduce the risk of Salmonella contamination.