Feeding antibiotic-contaminated waste milk to calves—Effects on physical performance and antibiotic sensitivity of gut flora

Abstract

The effect of feeding calves antibiotic-containing waste milk was studied in two trials. In the first trial both fermented and unfermented waste milk were fed and in the second trial only unfermented milk was used. The antibiotic-containing milk had a poor palatability and rejection rates were high. Growth rates of the calves were poor and in the second trial differed significantly from those of the control calves which had received milk substitute. Faecal E. coli were monitored for antibiotic resistance. In the first trial, the geometric mean minimal inhibitory concentration for streptomycin was significantly higher for isolations from calves fed antibiotic-containing milk, but no differences were observed for ampicillin. In the second trial, the percentage of resistant E. coli and enterococci was determined but no differences were observed between isolations from calves fed antibiotic-containing milk and the controls. The ambient conditions in the United Kingdom did not encourage the rapid natural fermentation, which would degrade the antibiotics and make it an acceptable food, and it was concluded that the high numbers of bacteria in the product may present disease risk.