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

Abstract

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