My Yorkie, Rosie loves tennis balls. She love eating them that is. Her poop would have that stuff all in it.Tennis balls are a choking hazard for large dogs. The way they are constructed, with that little bit of "give" to them, they can get wedged in a dog's throat, and they are all but impossible to remove once that happens. I've witnessed this and it's terrifying and heartbreaking. I personally won't have anything smaller than a Jolly ball around big dogs.
We stopped giving her those and switched to plastic balls (which are way too big for her to swallow, but she can still carry around).
These also last a lot longer and the kind I got has holes so I can put treats in it.