Table 13.

Effect on shedding of AMR E. coli and residues of feeding calves colostrum from cows treated during dry therapy

	Gonggrijp et al. (2015)a
Study design	Experimental study determining the effect of feeding colostrum from cows treated with cloxacillin 500 mg and 600 mg at dry‐off
Country	The Netherlands
Farm	10 conventional dairy farms
Treatment	1 group of cow‐calf couples with 500 mg cloxacillin as dry cow therapy, 1 group of couples with 600 mg; 1 control group of couples (no dry cow therapy)
Feeding scheme	Calves were fed colostrum and milk from their treated mother (cow‐calf couples)
Antimicrobials/concentration	The median concentration of cloxacillin in the colostrum was 148 μg/kg (mean 218 μg/kg) and in the second till fifth milkings 67 μg/kg (mean 94 μg/kg). One sample of the control group produced colostrum with 6.3 μg/kg
Amount calves	20 cow‐calf couples with 500 mg cloxacillin; 38 couples with 600 mg; 29 control couples
Method and criteria applied to interpret results	Escherichia coli from faecal swabs; antimicrobial residues in faecal samples; antimicrobial residues, E. coli and total aerobic and coliform germ count in colostrum: antimicrobial residues by LC–MS; E. coli, total germ count and coliforms on MacConkey agar +/− cefotaxim and disk diffusion test for cefotaxim and ceftazidime +/− clavulanic acid and cefoxitin; visual growth compared to resistant and susceptible control strain
Antimicrobial resistance	ESBL‐ and AmpC‐producing E. coli
Time animals tested for faecal shedding	Faecal samples at days 1, 7, 14, 21
Result	Cloxacillin was detected in 60% of the colostrum samples of cows treated with cloxacillin with a median concentration of 148 μg/kg (mean 218 μg/kg) in the colostrum and of 67 μg/kg (mean 94 μg/kg) in the second until the fifth milkings. There was no difference between residue levels in the colostrum between the cows with a dry therapy of 500 or 600 mg cloxacillin. On day 7 and day 14, significantly more positive faeces samples were collected than on day 1. No significant association has been found between the presence of ESBL/AmpC‐producing E. coli in calf faeces and in the colostrum and with the total aerobic germ count in colostrum. A higher amount of ESBL/AmpC‐producing E. coli in the calves, faeces was significantly correlated with a lower total coliform count in colostrum.
Main relevant results as reported in abstract	‘In 60% of the colostrum samples of cows treated with cloxacillin as dry cow therapy, residues were detected. Cloxacillin was not found in any of the calves faecal samples. There is no association between the prevalence of ESBL/AmpC‐producing E. coli in faeces of young calves and the use of cloxacillin as dry cow therapy, the presence of cloxacillin residues in the colostrum of calf faeces, the presence of ESBL/AmpC‐producing E. coli in the colostrum or in calf faeces and the total (aerobic) germ count of colostrum. A limitation of the study is that only cloxacillin therapy and ESBL/AmpC‐resistant E. coli have been tested and that cloxacillin does not select for ESBL/AmpC‐resistant isolates. Only an association was found between the prevalence of ESBL/AmpC‐producing E. coli in faeces of young calves and the total coliform count in colostrum. Calves without ESBL/AmpC‐producing E. coli in faeces, have significantly lower coliform counts in the colostrum compared to calves with ESBL/AmpC‐producing E. coli in their faeces. This could be explained by the fact that a large amount of other coliform bacteria are limiting the colonisation of ESBL/AmpC‐producing E. coli in faeces’
Main uncertainties and limitations of the study	Uncertainty relates to the fact that the study was carried out on 10 different dairy farms and no analysis was provided investigating the influence of the identity of the farm on the results. Therefore, influences of farm management could not be excluded. Also no information has been provided on the time between dry cow therapy and calf birth for each of the cow‐calve couples. A limitation of the study is that only cloxacillin therapy and ESBL/AmpC‐resistant E. coli have been tested and that cloxacillin does not select for ESBL/AmpC‐resistant isolates

ESBL: extended‐spectrum beta‐lactamases; LC–MS: liquid chromatography–tandem mass spectrometry.

^aSee Appendix D.