The use of medicinal zinc oxide (ZnO) must be phased out by 2022, thus prompting an urgent need for alternative strategiesto prevent diarrhoea in weaner piglets. The objectives of this study were to assess the impact on weaner piglet performance,diarrhoea incidence and gut development, when (1) dietary ZnO supplementation was substituted by alternative commercialproducts based on macroalgae, specific probiotics or synbiotics, or (2) dietary ZnO inclusion was reduced from 2500 to 1500 ppm.A total of 4680 DLY piglets (DanBred, Herlev, Denmark), weaned around 35 days of age, were randomly assigned according to sexand BW to six different dietary treatment groups. A basal diet was supplemented with no ZnO (NC=negative control), 2500 ppmZnO (PC=positive control), 1500 ppm ZnO (RDZ=reduced dose of ZnO) or commercial macroalgae (OceanFeed™Swine=OFS),probiotic Miya-Gold or synbiotic GærPlus products. The piglets entered and exited the weaner unit at ~7.0 and 30 kg BW,respectively. In-feed ZnO was provided the first 10 days post-weaning, while the alternative supplements were fed throughout theweaner period. As expected, the average daily feed intake, average daily weight gain (ADG), feed conversion ratio (FCR)anddiarrhoea incidence were improved in the PC compared to NC group (P<0.05) during phase 1 consistent with improved indices ofvilli development observed in subgroups of piglets sacrificed 11 days post-weaning. Reduction of ZnO to 1500 ppm lowered ADG(P<0.05) and slightly increased incidence of diarrhoea during the first 10 days after weaning (but not later) without affecting FCR.None of the three alternative dietary additives, including a 10-fold increased dose of GærPlus than recommended, improved pigletperformance, gut health and gut development above that of NC piglets. The OFS piglets sacrificed 11 days after weaning hadsignificantly lower weights of hindgut tissue and contents compared to the PC group, consistent with antimicrobial activity of theproduct, which was detected from anaerobicin vitrofermentation. In conclusion, dietary ZnO supplementation during the first10 days post-weaning may be reduced from 2500 to 1500 ppm without major negative implications for weaner piglet performanceand health in herds under a high management level. However, none of the alternative dietary supplements were able to improvepiglet performance or gut health, when ZnO was omitted from the diet.