Seresto has been extensively tested for its safety, including pets chewing on the collar or ingesting the entire collar. As the vast majority of active ingredients are bound in the collar matrix and not on the surface, the only side effect recorded after ingesting a full collar was a mild stomach upset (e.g. loose stools), which was resolved within 24 hours.

Seresto Large Dogs will fit. It's 27.5 inch and is adjustable.

Seresto is completely safe for cats, in fact there is Seresto for cats.

It shouldn't interfere with its effectiveness, however it is good idea to keep an eye on it.

I had one on my Golden Retriever and I still kiss & hug him every day! You can take it off for a while but it's not recommended.