BackgroundRecently, in-feed medicinal zinc has been phased out in pig production in the European Union. This makes updated knowledge about porcine post-weaning diarrhea (PWD) crucial. The objectives of the present study were to investigate (i) the clinical presentation of PWD in pigs housed in Danish herds that did not use medicinal zinc, specifically the prevalence of diarrhea and whether PWD was associated to clinical signs of dehydration or altered body temperature; (ii) which microorganism are associated to PWD; and iii) whether measurements of the fecal pH have a potential to be used diagnostically to differentiate between infectious etiologies in cases of PWD.ResultsThe prevalence of diarrhea varied considerably between the outbreaks in the nine studied herds (median = 0.58, range = 0.10; 0.94). In a cross-sectional design (n = 923), diarrhea was associated with reduced rectal temperature and alkaline feces. Diarrhea was also associated with observably reduced skin elasticity, possibly indicating dehydration. In both diarrheic case pigs (n = 87) and control pigs (n = 86), the presence ofBrachyspira pilosicoli,Clostridium perfringens,Cryptosporidiumspp.,Cystoisopora suis,enterotoxigenicEscherichia coli,Lawsonia intracellularis, porcine circovirus types 2 and 3, rotavirus A, B, C, and H,Samonella enterica spp. enterica, andTrichuris suiswas described. PWD was associated with high levels of enterotoxigenicE. colishedding (odds ratio versus noE. colidetection = 4.79 [CI 1.14; 12.62]). Diarrhea was associated with high levels of rotavirus A shedding (odds ratio versus no/low rotavirus A = 3.80 [CI 1.33; 7.97]). The association between microbiological findings in diarrheic pigs and fecal pH was negligible.ConclusionsEnterotoxigenicE. coliwas confirmed to be a cause of PWD; however, cases of PWD where enterotoxigenicE. coliwas not detected in high levels occurred commonly, and this adds to the increasing evidence suggesting that PWD is not necessarily a result of enteric colibacillosis. Rotaviral enteritis might be a differential diagnosis of PWD. pH-measurements cannot be used to differentiate between differential diagnoses for PWD.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40813-023-00325-x.