Assistance in the update of the systematic literature review (SLR): 'Influence of copper on antibiotic resistance of gut microbiota on pigs (including piglets)'
A total of 901 references were examined to assess the influence of copper supplemented diets on copper and antibiotic resistance of gut microbiota in pigs (including piglets). Merely 33 references were found eligible to answer this review question. From these 33 references, eleven references were assigned as experimental field studies, ten references were experimental environmentally controlled studies, and twelve references were assigned as cross-sectional studies. The references assigned as experimental field studies provided the most suitable information for the review question. The other studies gave useful information concerning the mechanism of resistance or prevalence of resistant isolates. The overall methodological quality of the field studies was rather poor. Only three of the eleven field studies had a methodological quality that was considered acceptable for the present review question. Therefore, the restricted number of studies available from the SLR, and the limitations in terms of results and methodological quality do not allow excluding the possibility of a positive correlation between copper supplementation above requirements and development of antibiotic resistance