A Cow with a Window?

In doing my Google research, I found that there is indeed such a thing as a "cow with a window". Its not exactly a glass window, but there are agriculture research projects that study the digestive systems of cows by creating a hole in the cow that leads directly to its stomach. The main purpose of this is to study the ways that various foods digest within the cow. I imagine this allows researchers to create foods that are easier for cows to digest and more cost efficient for farmers.

Here you can see the plug used to cover the fistulated cow, and when open you can see that the food is easily accessible to anyone motivated enough to reach inside...