Farming practices in Sweden related to feeding milk and colostrum from cows treated with antimicrobials to dairy calves

Abstract

BackgroundMilk produced by cows in receipt of antimicrobial therapy may contain antimicrobial residues. Such antimicrobial-containing waste milk must be withdrawn from human consumption and is therefore sometimes used as calf feed. Unfortunately, this approach might promote selection of antimicrobial resistant bacteria in the calves’ intestinal microbiota. The objectives of this study were therefore to obtain an overview of waste milk feeding practices on Swedish dairy farms and to investigate if these practices were associated with certain farm characteristics. A representative group of 457 Swedish dairy farmers participated in a web-based survey with questions about the use of colostrum and milk from cows treated with antimicrobials at dry off or during lactation, respectively, as calf feed.ResultsColostrum (milk from the first milking after calving) and transition milk (milk from the second milking to the fourth day after calving) from cows treated with antimicrobials at dry off was fed to calves on 89% and 85% of the farms in the study, respectively. When antimicrobial therapy was given to cows during lactation, 56% of the farms fed milk that was produced during the course of treatment to calves, whereas milk that was produced during the subsequent withdrawal period was fed to calves on 79% of the farms. Surveyed farmers were less prone to feed such milk if the antimicrobial therapy was due to mastitis than other infections. In Sweden, a majority of antimicrobial treatments during lactation are systemic administration of benzylpenicillin and thus, the bulk of waste milk in Sweden is likely to contain residues of this drug. Feeding waste milk to calves was more common on non-organic farms, and on farms located in Southern Sweden, and was less common on farms with cows housed in cold free stalls barns.ConclusionsWaste milk that may contain antimicrobial residues is, at least occasionally, used as feed for calves on a majority of surveyed Swedish dairy farms. Future work should focus on the effect of waste milk feeding on the occurrence of antimicrobial resistant bacteria in the calves’ intestinal microbiota.

Risk factors for antimicrobial resistance in fecal Escherichia coli from preweaned dairy calves

“…A web-based questionnaire survey was conducted in 2011 to obtain information describing farming practices related to feeding milk and colostrum from cows treated with antimicrobials to calves (Duse et al, 2013). The questionnaire is described in detail in Duse et al (2013).…”

“…The survey inquired about farming practices related to feeding of colostrum and milk from cows treated with antimicrobials (Duse et al, 2013). As the final question in the survey, respondents were given the opportunity to participate in the current study by submitting calf fecal samples for susceptibility testing.…”

“…A web-based questionnaire survey was conducted in 2011 to obtain information describing farming practices related to feeding milk and colostrum from cows treated with antimicrobials to calves (Duse et al, 2013). The questionnaire is described in detail in Duse et al (2013). Colostrum and transition milk (i.e., milk from the second milking to the fourth day after calving) from a cow that was treated with antimicrobials at dry off were designated waste colostrum (WC) and waste transition milk (WT), respectively.…”

“…Such milk may contain residues of antimicrobials Randall et al, 2014), which may impose selection pressure on the calves' gastrointestinal bacteria and favor resistant strains. This practice may explain the high prevalence of resistant E. coli in preweaned calves (Brunton et al, 2012;Aust et al, 2013;Duse et al, 2013). A few studies have investigated the effect of this feeding practice.…”

“…During the period when the prevalence of resistance peaks, it is likely that calves are exposed to antimicrobials via ingestion of milk or colostrum from cows treated with antimicrobials. Feeding milk from treated cows is a common practice on many dairy farms (Brunton et al, 2012;Duse et al, 2013). Such milk may contain residues of antimicrobials Randall et al, 2014), which may impose selection pressure on the calves' gastrointestinal bacteria and favor resistant strains.…”