Effects of feeding pasteurized waste milk or saleable milk to calves on weight, health and fecal Escherichia coli antimicrobial resistance

CELLONE, IVANA; RUSSI, NORMA; CALVINHO, LUIS F.; SIGNORINI, MARCELO; MOLINERI, ANA

Journal of Dairy Research

CAMBRIDGE UNIV PRESS

Año: 2024 p. 1 - 7

0022-0299

The aim of this study was to compare the effects of feeding pasteurized waste milk or saleablemilk to calves on weight, health and emergence of antimicrobial resistance in Escherichia colistrains isolated from those calves. An experimental study under field conditions on a commercialpasture-based Argentinian dairy farm was carried out. Forty Holstein calves were assignedrandomly to either pasteurized waste milk (PWM) or non-pasteurized saleable milk (SM).The antimicrobial agents (AM) used on the farm, both to treat or prevent diseases, wererecorded. The passive immunity level, calf live weight, AM presence in milk, clinical examinationof calves, and E. coli isolation and identification, were performed. A total of 258 E. colistrains were isolated from fecal samples (132 isolates from SM calves and 126 from PWMcalves at six sampling times). All E. coli isolated were used to perform AM susceptibilitytests (disc diffusion and agar dilution). No differences were observed between groups in healthparameters, average daily gain or prevalence of resistant E. coli strains to any AM evaluatedthroughout the study. Peaks of trimethoprim, sulfamethoxazole and enrofloxacin minimuminhibitory concentration (MIC) were observed at 30 d in E. coli from both groups of calves,whilst additional peaks to tetracyclin and ampicillin were observed only in SM calves. AllMIC apart from gentamicin decreased at 75 and 90 d of age (during the weaning period).Gentamicin MIC behaved differently, having no peaks and increasing at 90 d only in PWMgroup. In conclusion, we found no evidence that emergence of antibiotic resistance is relatedto the consumption of pasteurized waste milk.