I have noticed this ever since I've had Pearl (she is 18 months old) When she has a poop she spends ages digging so her bottom is already protruding and poop starting to come out when she squats to go.
What worries me a little is the skin from her bottom looks bright red like blood but it's not blood, she has no pain and when she has finished it goes back and it looks like a normal bottom again.
It has always been this colour I don't know if this is the normal colour of the inside of her bottom or not.

_________________
Clare
Magic (brown spotted boy born 31 March 2012)
Pearl (seal Lynx Point girl born 1 October 2015)
Bristol, UK

I am the worst when it comes to making sure Raiden goes to the vet any time I find something suspicious. His vet is 2 miles down the road, so it is easy and convenient and I can just walk in there with him and have him examined. I'd hope his only visit is his annual wellness exam and vaccinations, but we have already been at the vets three times this year. And he has an August appointment for his dental cleaning.

Clare, if you are concerned, which you are, I'd take Pearl to the vet to have it checked out -- or at least CALL the vet and ask the question. If they think it could be serious, they might want to see her. Don't just assume something is wrong, or it's normal. We'd all be veterinarians if we could do that! LOL