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Keywords:

  • dairy;
  • Escherichia coli ;
  • forage;
  • Mycobacterium;
  • organic acids;
  • paratuberculosis;
  • Salm. Typhimurium;
  • Salmonella ;
  • silage

Abstract

Aims

To evaluate the persistence of Mycobacterium avium subsp paratuberculosis (Mycoparatuberculosis), Salmonella enterica serotype Typhimurium (Salm.Typhimurium) and a commensal Escherichia coli (E. coli) isolate under the low pH and high organic acid (OA) conditions of ensiling of forages.

Methods and Results

Decay rates and the time required to obtain a 90% reduction in cell concentration were calculated following (i) exposure to buffered OA (pH 4·0, 5·0, 6·0 or 7·0) (ii) exposure to silage exudates and (iii) survival through ensiling of forage materials. Salm. Typhimurium had higher decay rates in silage exudates (−0·5601 day−1) than did E. coli (−0·1265 day−1), but both exhibited lower decay rates in silage than in OA or silage exudates. Mycoparatuberculosis showed no decrease in silage and decay rates in silage exudates were significantly lower (2–12 times) than for the other two organisms.

Conclusions

Escherichia coli, Salm. Typhimurium and Mycoparatuberculosis exhibit marked differences in response to acidity. All three organisms show acid resistance, but Mycoparatuberculosis in particular, if present in manure and applied to forage grasses, may survive the low pH and high OA of the ensilaging process; silage may therefore be a potential route of infection if ingested by a susceptible animal.

Significance and Impact of Study

This information contributes to the understanding of potential risks associated with silage preservation and contamination of livestock feed with manure-borne pathogens.