Hi Juliesjazz and Midnightsun,
CLW here. Thank you for sharing your experience using the Metronidazole. I think that is a great approach to this sloppy stool issue. I had not thought of using that with horses. I have used it on several rescued cats with chronic diarrhea and it was the only thing that worked.
My 20 year old Morgan gelding that started this whole thread of this topic is stabilized and is now off herbal allergy blend. I stay away from coarse/ mature or over mature first cut grass hays. That seems to have an effect on him. fine softer later cuttings work very well for him.
With respectful regard