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in Journal of the American Veterinary Medical Association


OBJECTIVE To determine whether feeding a direct-fed microbial (DFM) to dairy calves would reduce total and antimicrobial-resistant coliform counts in feces and affect average daily gain (ADG).

ANIMALS 21 preweaned Holstein heifer calves.

PROCEDURES The study had a randomized complete block design. Within each block, 3 consecutively born calves were randomly assigned to 1 of 3 treatment groups within 24 hours after birth (day 0). Calves were fed the DFM at 1.0 g (DFM1; n = 7) or 0.5 g (DFM2; 7) twice daily or no DFM (control; 7) from days 0 through 29. A fecal sample was collected from each calf daily on days 0 through 3 and then every other day through day 29. Fecal samples were cultured, and mean numbers of total coliforms and coliforms resistant to ampicillin, ceftiofur, and tetracycline were compared among the 3 treatment groups. Calves were weighed on days 0 and 29 to calculate ADG.

RESULTS Mean total fecal coliform counts did not differ significantly among the 3 treatment groups. Mean ceftiofur-resistant and tetracycline-resistant coliform counts for the control group were significantly lower, compared with those for the DFM1 and DFM2 groups. Mean ADG did not differ significantly between the DFM1 and DFM2 groups; however, the mean ADG for all calves fed the DFM was 0.15 kg less than that for control calves.

CONCLUSION AND CLINICAL RELEVANCE Results suggested that the DFM fed to the preweaned calves of this study did not reduce total or antimicrobial-resistant coliform counts in feces.

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in American Journal of Veterinary Research