Rabbit has large, soft poo

Question
We adopted a Rex bunny at the shelter yesterday.  He had been in there since last July.  Apparently, while there he had problems with large soft poo (not diarrhea or not cecotrophs).  They told us in last couple of months, he's been better while on Martin's pellets.  

They did a few fecal tests on him and they came back normal.  They can't figure it out.  I noticed this AM he did have large soft poo and I'm a little concerned.  It was his first night with us but he ate hay/all his pellets (about 1/4 cup) and a some veggies (I don't give a lot to new ones right off).  He drinks too and behaves normally otherwise.  

Could it just be nerves again being at a new place?  I was given Fenbendazole by the shelter to give him .4cc per day for 3 days, then in 2 weeks for 3 days again.  I will give him his first dose tonight.

I hope you have some ideas.  Thank you.  
P.S. They don't know his age but by the way he acts, he's not an old bunny.

Answer
Dear Paula,

This might seem like a strange question, but:  What color is the bunny?

If he's white with dark markings and dark eyes, he might have a congenital condition often linked with this color pattern.  It's sometimes called "megacolon", but I personally think that's a misnomer, as no one knows for sure whether it bears any physiological similarity to the megacolon condition seen in other mammals.

In my experience, these "Cowpoop Syndrome" bunnies appear to produce pellets that are a combination of both fecal and cecal matter, and the weird texture might be due to faulty anatomy or innervation of the cecal/intestinal junction.  But that's just a guess.

The condition can't be cured, but it's important to know that it can have severe complications, especially if the bunny's intestinal contents become dehydrated.  A large, desiccated poop like this can cause an intestinal obstruction and this must be avoided by making sure the bunny gets LOTS of oral hydration via water and wet greens.  It also can help (if this bunny has the syndrome I'm talking about) to give the bunny a dose of lactulose once or twice a week. This osmotic laxative will draw liquid into the intestine and keep the big, marshmallowy poops soft and easy to pass.

We had a bunny who eventually died of complications from this syndrome. She had three surgeries to remove intestinal obstructions, and on the first one the vet noticed that her intestine had scarring and stenosis all along its length.  I wonder whether this was caused by intermittent hard stools, and whether poor Gypsy might not have died if we had known to keep her on a regimen of lactulose regularly to prevent this.  

I still don't know if it would have helped.  But I do know that the other Cowpoop Bunnies we've had on lactulose have so far never had any intestinal obstructions.  (knock wood!)

It's not a bad idea to worm her with fenbendazole, just in case.  But don't expect miracles.  If this is Cowpoop Syndrome, you might be in it for the long haul.

You can find an experienced rabbit vet here:

www.rabbit.org/vets

whom you can consult about this, and ask about the lactulose.

Hope this helps.

Dana