| Summary: | Two experiments were conducted to evaluate fecal shedding of E. coli O157:H7 in newly-weaned calves. In the first experiment, twenty-four heifers were fed a basal diet composed of wheat middlings and corn grain (15% CP and 79% TDN). Twelve heifers were supplemented with trace minerals to provide an additional 399 mg Cu, 1001 mg Zn, and 707 mg Mn/d. The control diet had no supplemental trace minerals added. All heifers were inoculated with an oral dose of 1010 CFU of E. coli O157:H7. Fecal samples were collected every 18 h for the first three days after dosing and then every three d until d 21 to determine E. coli O157:H7 shedding rates. On d 7 venous blood was collected, and on d 21 liver tissue and venous blood were collected. Trace mineral supplementation did not increase IBR titers (P=0.50) but increased (P<0.005) liver Cu concentration. There were no differences in the rate of fecal shedding of E. coli O157:H7 between treatments, but the SEM between treatments often were as great as the mean values. E. coli O157:H7 decreased in concentration during the first 21 d. Unexpectedly, after d 21, fecal E. coli O157:H7 concentration increased to a level measured 18 h post-inoculation. These results suggest that supplemental trace minerals did not influence the rate of E. coli O157:H7 shedding. This may be due to a lack of nutritional stress on the animals (no differences in IBR titers), or because the control diet provided adequate trace minerals. In the second experiment, 374 steers were split into two groups to determine if an experimental E. coli vaccine would reduce fecal shedding of E. coli O157:H7 during the first 56 d after weaning. Calves did not shed E. coli O157:H7 during either sampling period (d 0 or d 55). There was no difference in fecal shedding of the bacteria between the control and vaccinated treatments. There was, however, an unexplained difference (P < 0.0001) in ADG, with vaccinated calves gaining 0.11 kg/d more than the control treatment. These data indicate that E. coli O157:H7 is not a problem at this ranch in Montana.
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