How was he acting agood while after he passed this messy poop? Medications can cause poop to become abnormal. Not moving around as normal would also impact some on the digestive track. I do wonder if he had impacted cecum (speculation on my part) and was able to pass this and normalize again?

@Bunny House, it’s really interesting you brought up sarcocystis. Id just been emailing the other FL’s about posting a topic about it on the forum here. It’s good there is a growing awareness about it. I actually saw it mentioned again in relation to “Floppy Rabbit Syndrome”

PJ&Me, there is a now retired rabbit vet in the UK that is conducting some studies to try discern more about Floppy Rabbit Syndrome. I’ll just share this quote with you from her site, as it does cover some things you are already looking into with PJ. As you can see, it’s a bit of a blanket term, the condition having several possible causes.

The cause of FRS is unclear. Little or no scientific literature exists on the clinical presentation, pathologic changes and potential underlying processes of FRS patients. Infectious causes (Encephalitozoon cuniculi, Toxoplasma gondii, Sarcocystis cuniculi, and Clostridium botulinum), metabolic causes (hypokalaemia, vitamin E/selenium deficiency), plant toxicity and myasthenia gravis have all been put forward as potential aetiologies but there is no supporting evidence for any of these ideas. Paralysis due to trauma is another possibility. At the present time, the diagnosis of FRS is entirely based on clinical suspicion, supported by neurological examination and exclusion of other causes. Blood sampling for antibodies to Encephalitozoon cuniculi is important as this is the major differential diagnosis. Investigations are underway (see below) to see if a specific blood test for FRS is al possibility. More expensive tests such as CT/MRI scanning, cerebrospinal fluid analysis and electromyelography can also help with making a diagnosis but are not widely available. They can show another problem (e.g. a tumour or fractured spine) that could be causing the clinical signs. ~Frances Harcourt-Brown