Can rubber mulch be harmful to dogs?

Factual Questions
1

I’m thinking of using rubber mulch as a ground cover for a dog run. Can it be harmful to dogs?

Thanks!

2

I guess if your dog likes to eat it, it could be.

3

15 cubic yards of it hasn’t killed my young kids. The local critters and outdoor pets avoid it because it’s not a good place to poop.

4

Here’s a similar thread from last year. One poster suggests that rubber dog toys will pass undigested, although I don’t know if that extends to rubber mulch.

5

If the dogs ate a bunch of it AND it caused intestinal obstruction, then yes, it would be a problem.

How big are the dogs vs. how big are the mulch pieces?