The effect of bovine diet on Salmonella survival in synthetic abomasal fluid

Abstract

Aims: To investigate the effect of diet on the survival of Salmonella in the bovine abomasum.

Methods and results: Five fistulated cows were randomly assigned to one of five diets denoted as: (i) 100% grass, (ii) grass + 5·3 kg DM concentrate, (iii) 100% grass silage, (iv) 100% hay and (v) maize/grass silage plus concentrates. Rumen fluid was harvested from each dietary treatment and inoculated with nonacid (NA) and acid-adapted (AA) 5-strain Salmonella cocktails. After 24-h incubation period, Salmonella were acid challenged to synthetic abomasum fluid (SAF, pH 2·5) for 5 h to determine their resistance to low pH. The study found that the volatile fatty acids composition and the pH profile of bovine rumen fluid were significantly altered (P <0·05) by some of the dietary treatments but not others. Regression analysis found that significantly higher numbers of acid-adapted Salmonella survived in SAF after incubation in rumen fluid from diets 1, 2 and 4, but fewer significant differences were found between diets for nonacid-adapted Salmonella. The results suggest that the acid-adapted cells were subjected to a higher level of cell injury than the nonadapted cells.

Conclusions: Pre-incubation in rumen fluid did influence the resistance of nonacid and acid-adapted Salmonella to SAF but it was dependant on the dietary treatment fed to the cows.

Significance and impact of the study: This study examined the use of diet, as a modulating factor to limit the bovine excretion of Salmonella with a view to providing a scientific basis for the design of dietary management controls in the future.