The effect of feed withdrawal on Escherichia coli shedding in beef cattle

Ten beef cattle feeding on silage were orally administered a marker organism (nalidixic acid resistant Escherichia coli K12) daily over six days. Subsequently, the administration of the marker organism was stopped, and the animals were divided into two groups (five animals each). The feed was removed from one group (i.e. fasted group) for 48 h, while the feeding of the control group was continued during that period, until both groups were subsequently slaughtered. During this pre-slaughter period, faecal shedding of total E. coli and E. coli K12, as well as of background flora (total aerobes, total anaerobes, and lactobacilli), was monitored in faecal material obtained by rectal swabs from each animal. After both 24 and 48 h of fasting, the levels of total E. coli shed significantly increased (P<0.01) in the fasted group compared with the control group; total anaerobes shed also increased (after 48 h fasting; P<0.05); while shedding of total aerobes and total lactobacilli did not change significantly. After slaughter of animals, the pH values and the levels of bacterial groups mentioned above were examined in contents of different sections of the gastrointestinal (GI) tract (rumen, abomasum, caecum, small intestine, colon). The pH values were significantly increased in rumen and decreased in abomasum (P<0.05) of the fasted animals compared with controls, but did not differ significantly in other GI sections. Significant decreases of total E. coli population (P<0.05) in abomasums and lactobacilli (P<0.01) in small intestines were observed in fasted animals, while other bacterial groups in other GI sections did not change significantly compared with controls. The marker organism E. coli K12 was not sufficiently competitive within the bovine GI tracts as it was pre-slaughter shed by, and post-slaughter isolated from, only a minority of animals regardless of the group. Overall, the results indicate that key fasting-induced changes of enteric E. coli populations, and influencing its faecal shedding, could have occurred within the relatively short caudal colon–rectum–anus region of the bovine GI tract.