The objective of this study was to determine the effect of nutrient density and housing on E. coli populations in beef and dairy production systems. In the first trial, sixty second trimester beef cows were housed in two different overwintering environments and provided dry hay which was either bale grazed or placed in a feed bunk. Selected pens had supplemented with dried distiller’s grain with soluble (DDGS; 2.5 kg/cow/every third day) or rolled barley (1 kg/cow/day). In the second trial, six rumen and caecal-cannulated, non-lactating, multiparous Holstein cows received one of the following diets: i) 70% forage ii) grain pellet or iii) alfalfa pellet. The latter two diets were formulated to induce subacute ruminal acidosis (SARA). All animals were randomly sorted to pens and treatments. Fecal samples were collected and cultured on selective media. E. coli were enumerated and three isolates were chosen for PCR to detect the presence of 18 selected genes encoding a range of virulence factors. These same isolates were tested for their ability to invade the human adenocarcinoma epithelial cell line HT-29. Diet did not significantly affect E. coli abundance but did influence the prevalence of virulence genes involved in adhesion of bacteria to epithelial surfaces. When the diet contained grain, cows shed isolates which were more invasive than those from cows in the other treatments. The data suggest that diet may affect the abundance of E. coli shed in the feces and increase the presence of E. coli harbouring particular virulence genes that mediate adhesion and invasion of epithelial surfaces.

The objective of this study was to determine the effect of nutrient density and housing on E. coli populations in beef and dairy production systems. In the first trial, sixty second trimester beef cows were housed in two different overwintering environments and provided dry hay which was either bale grazed or placed in a feed bunk. Selected pens had supplemented with dried distiller’s grain with soluble (DDGS; 2.5 kg/cow/every third day) or rolled barley (1 kg/cow/day). In the second trial, six rumen and caecal-cannulated, non-lactating, multiparous Holstein cows received one of the following diets: i) 70% forage ii) grain pellet or iii) alfalfa pellet. The latter two diets were formulated to induce subacute ruminal acidosis (SARA). All animals were randomly sorted to pens and treatments. Fecal samples were collected and cultured on selective media. E. coli were enumerated and three isolates were chosen for PCR to detect the presence of 18 selected genes encoding a range of virulence factors. These same isolates were tested for their ability to invade the human adenocarcinoma epithelial cell line HT-29. Diet did not significantly affect E. coli abundance but did influence the prevalence of virulence genes involved in adhesion of bacteria to epithelial surfaces. When the diet contained grain, cows shed isolates which were more invasive than those from cows in the other treatments. The data suggest that diet may affect the abundance of E. coli shed in the feces and increase the presence of E. coli harbouring particular virulence genes that mediate adhesion and invasion of epithelial surfaces.