Table 17.

Possible measures with regard to feeding calves milk from cows treated with antimicrobials during lactation

Measure	Evidence in support of the measure	Evidence against the measure	Advantages	Disadvantages
L1 Allow use of milk during treatment and withdrawal period irrespective of antimicrobial or administration route	Direct No evidence from studies (3.4.1)	Direct Increased shedding of AMR bacteria by calves fed waste milk in an observational study (Duse et al., 2015) and in three experimental studies (Langford et al., 2003; Aust et al., 2013; Brunton et al., 2014) (3.4.1) Increased shedding of antimicrobial resistant bacteria by calves fed milk spiked with antimicrobials in three experimental studies (Berge et al., 2006; Alali et al., 2004; Pereira et al., 2014) (3.4.1) Indirect In lactating cows, residue levels will be higher after intramammary than after systemic treatment (3.2.4) Antimicrobial concentrations in milk during treatment will be higher than the MIC but then decline (3.2.4)	No interference with current routines on dairy farms	Increased shedding of AMR bacteria by calves
L2 Prohibit use of milk during treatment and withdrawal period irrespective of antimicrobial or administration route	Direct Increased shedding of AMR bacteria by calves fed waste milk in 1 observational study (Duse et al., 2015) and in three experimental studies (Langford et al., 2003; Aust et al., 2013; Brunton et al., 2014) (3.4.1) Increased shedding of AMR bacteria by calves fed milk spiked with antimicrobials in three experimental studies (Berge et al., 2006; Alali et al., 2004; Pereira et al., 2014) (3.4.1) Indirect Antimicrobial concentrations in milk during treatment will be higher than the MIC but then decline (3.2.4)	Direct No evidence from studies (3.4.1)	Reduced risk for shedding AMR bacteria by calves	Loss of waste milk as valuable feed for calves Low compliance if not well founded and communicated Disposal of waste milk could increase residues in the environment
L3 Prohibit use of milk from cows treated with highest priority CIAs during treatment and withdrawal period	Direct In a dairy herd using cefquinome to treat cows, calves receiving waste milk shed greater numbers of cefotaxime resistant E. coli than calves receiving milk replacer (Brunton et al., 2014) Indirect Antimicrobial concentrations in milk during treatment will be higher than the MIC but then decline (3.2.4) Applied in FI and apparently is practically applicable	Direct No evidence from studies (3.4.1)	Reduced risk for shedding bacteria resistant to CIAs by calves Ameliorates some disadvantages of a complete ban (L2) To focus on highest priority, CIAs targets resistance of most public health significance and could also be a lever for reducing the use of these antimicrobials	Disadvantages as for L2 on farms using CIAs Separation of milk by treatment includes practicalities that might interfere with compliance
L4 Prohibit use of milk during treatment but allow use of milk during the withdrawal period Could be limited to highest priority CIAs	Direct No evidence from studies (3.4.1) Indirect Antimicrobial concentrations in milk during treatment will be higher than the MIC but then decline (3.2.4) This measure is recommended in some MSs and apparently is practically applicable	Direct In an observational study there was no difference in shedding of AMR E. coli by calves fed milk during treatment or withdrawal (Duse et al., 2015) Indirect Relatively low antimicrobial residue levels may induce equal or even more resistance compared to higher levels	Reduced risk for shedding AMR bacteria by calves. Ameliorates some disadvantages of a complete ban (L2)	Partial loss of waste milk as valuable feed for calves Low compliance if not well founded and communicated Separation of milk fractions from individual cows includes practicalities that might interfere with compliance Disposal of waste milk might increase residues in the environment
L5 Prohibit use of milk during treatment and withdrawal period from cows treated intramammary but allow use of milk from cows treated systemically. Could be limited to milk during treatment; to highest priority CIAs; or to the highest priority CIAs during treatment	Direct No evidence from studies (3.4.1). Indirect In lactating cows, residue levels will be higher after intramammary than after systemic treatment (3.2.4) Antimicrobial concentrations in milk during treatment will be higher than the MIC but then decline (3.2.4)	Direct No evidence from studies (3.4.1)	Reduced risk for shedding antimicrobial resistant bacteria by calves Ameliorates some disadvantages of a complete ban (L2)	Since the majority of lactating cows are treated by the intramammary route this measure would have largely similar implications as a complete ban (L2)
L6 Allow use of milk after treatment to reduce residue levels	Direct Some milk treatment methods, mainly to remove β‐lactam antimicrobials, are described (3.6.2 and Table 18)	Direct Evidence on activity spectrum towards different antimicrobials is lacking (3.6.2 and Table 18)	Ameliorates some disadvantages of a complete ban (L1). Probably higher compliance than to a complete ban	Practicality at the farm level is not obvious and might interfere with compliance Potential impact on nutritional and properties of the milk A need to adapt and evaluate methods for practical use
L7 Allow use of milk after treatment to reduce bacterial load	Direct No evidence from studies that AMR bacteria in waste milk increase shedding by calves (3.4.1) Some milk treatment methods to remove bacteria are described (3.6.3 and Table 19)	Direct Pasteurisation of milk containing antimicrobial residues had no effect on the increased faecal shedding of antimicrobial‐resistant E. coli. (Aust et al., 2013) (3.4.1)	Ameliorates some disadvantages of a complete ban (L1) Probably higher compliance than to a complete ban	Practicality at the farm level is not obvious and might interfere with compliance Potential impact on nutritional and properties of the milk A need to adapt and evaluate methods for practical use

AMR: antimicrobial resistance; FI: Finland.

CIA: critically important antimicrobial for human medicine, e.g. 3rd–4th generation cephalosporins and fluoroquinolones, according to the WHO definition (Collignon et al., 2016; WHO, 2016). See Appendix A.