Cannulated Cow - Stick Your Hand Inside?

A day ago, while I was reasearching about the benefits of cannulated over non-cannulated screws for fractured ankle, I stumbled upon a website called "Cannulated Cows"! Immediately it caught my attention.
Click!
And OMfG! All I could think of is animal cruelty! animal torture!
So what exactly is 'cannulated cow'??
Cannulated cow is a poor cow that has been surgically fitted with a cannula: which acts as a porthole-like device that allows access to the rumen (digestive system) of the poor cow. Actually this activity can be traced back to as early as the 1920's.
They claimed that animals can live perfectly well with a permanent hole in their stomachs. Scientists call these surgically made holes, fistulas, which are covered by a canulla, a sort of cover from the outside world. They are used to test the digestibility of various cattle food, the cows are fed and as the food passes through her stomachs, scientist can just reach in and see how it is processed. As brutal as it might look, they claimed that this doesn’t hurt the animals at all, it actually prolongs their life, in case of stomach disease, they can receive helping medicine directly in there.
The one thing I don’t approve of is people sticking their hands in to the poor cow just out of curiosity. Sure it’s not something you’d call ordinary, but turning a medical procedure into a circus isn’t very ethical.