Abstract
Feeding waste milk containing antimicrobial residues (WMA) to calves has been associated with increased antimicrobial resistance in calves' commensal bacterial flora. The objectives of this study were (1) to document practices related to the disposal of WMA on Swiss dairy farms and (2) to evaluate the association between farm characteristics and the feeding of WMA to calves. A web-based questionnaire on practices surrounding waste milk disposal was completed by 1,625 dairy producers (10.9% of solicited producers). Logistic regression models were built to evaluate the association between herd characteristics and the practice of feeding WMA. Waste milk produced during and up to the first milking after completion of antimicrobial treatment or during the withdrawal period was fed to at least some of the calves on 47.3% of respondents' farms. Farms in organic production had lower odds of feeding WMA to calves than nonorganic farms [odds ratio (OR) 0.59]. Farms located in the eastern region of Switzerland, as opposed to those in the western region, had increased odds of feeding WMA to calves (OR 2.01). A yearly average bulk tank somatic cell count ≥150,000 cells/mL was associated with increased odds of feeding WMA to calves compared with the reference category of <100,000 cells/mL (OR 1.62). An average cow-level annual milk production ≥8,500 L was associated with increased odds of feeding WMA to calves compared with farms in the interquartile range with a production of 6,500 to 8,499 L (OR 1.24). Further research is warranted to investigate dairy farmers' motivations affecting this practice, and to quantitatively define calves' exposure to antimicrobial residues and the resulting antimicrobial resistance in calves' commensal flora on these farms.
Highlights
Antimicrobial resistance (AMR) is a major concern in human and veterinary medicine
When asked to rank the methods they use for the disposal of waste milk containing antimicrobial residues (WMA), the median
The primary objective of this study was to estimate the prevalence of practices related to the disposal of WMA among Swiss dairy farms, with the practice of feeding WMA to calves being of special interest
Summary
The feeding of nonsalable or waste milk containing antimicrobial residues (WMA) to calves has come under scrutiny. This practice has been associated with increased AMR in calves’ commensal microbial flora (Duse et al, 2015; Maynou et al, 2017; Foutz et al, 2018; Jarrige et al, 2020), in addition to affecting gastrointestinal and respiratory microbiomes (Deng et al, 2017; Maynou et al, 2019; Zhang et al, 2019) and calves’ health (KleinJöbstl et al, 2015; Zou et al, 2017; Calderón-Amor and Gallo, 2020). When not fed to calves, WMA is often disposed of with manure, where antimicrobial residues could contribute to the persistence of antibiotic resistance genes and their dispersal in the environment (Jechalke et al, 2014; Ricci et al, 2017)
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