Many hens can just simply have poop caked on their excess feathers, especially if they have a water stool. I would clean off the vent areas with warm soapy water, and then why dry, trim the excess feathers from around the vent. Look at that time for parasites such as lice or mites. If your hens are bloated or over weight, they could be suffering from fatty liver disease, ascites, internal laying, or an enlarged crop. Check the crops to see that they are emptying by early morning. feel the breast bone for excess weight or loss of weight there, while feeling of the lower abdomen for spongy or tight skin. You may also consider worming your flock, and then starting them on probiotics in their water twice a week to help clear up the diarrhea.