Evaluation of the effects of weaning diets on Escherichia coli O157 shedding, body weight, and fecal bacterial communities in beef calves.

Cattle are considered to be one of the primary reservoirs of Escherichia coli O157. In this study, the effects of weaning diets on E. coli O157 shedding, body weight, and fecal bacterial communities in beef calves were evaluated. A total of 60 calves (28 heifers and 32 steers) were weaned and randomly assigned into two groups. A peanut/soy hull-based diet (Dry Feed, DF) and a corn silage-based diet (High Moisture, HM) were fed to the two groups, respectively, during the weaning and preconditioning period. Calf body weight was measured before weaning (BW) and 14 days after weaning (AW14), and a fecal sample was collected from each calf at BW, AW14, as well as 56 days after weaning (AW56). The prevalence of O157 in feces was determined by CHROMagar(™) O157 and polymerase chain reaction (PCR). Denaturing gradient gel electrophoresis (DGGE) was employed to analyze fecal bacterial communities. A significant decrease in body weight was observed during weaning, regardless of the calf diet (p<0.05). Calves fed the HM diet lost more weight than the DF-fed calves determined at 14 days after weaning (p<0.05). Both the CHROMagar(™) and PCR results showed that the overall prevalence of O157 increased significantly during weaning. Based on the CHROMagar(™) method, O157 increased from 16.6% at BW to 38.3% at AW14 (p<0.05) and stayed at the higher level during the preconditioning period (AW56). The increase in O157 prevalence was observed in HM-fed calves during weaning but not in DF-fed ones. Weaning also changed the profile of fecal bacterial communities (p<0.05). These results showed that weaning is a critical step in beef cattle production, not only because of its effects on body weight but also due to its impact on O157 shedding and gastrointestinal tract bacterial community establishment.