Here's the article I got it from:

https://www.animalsciencepublications.org/publications/jas/p...

In the third picture, the rumen has become pressurized from bloat, a condition they get when something stops them from belching (often the wrong sort of microbial activity in their rumen).

Research animals have "ports" inserted so researchers can see various stages of digestion.

https://en.wikipedia.org/wiki/Cannulated_cow

This allows them to make sure things like "cow magnets" aren't going to be harmful