The stomach of a cow is a fascinating place to explore. And any Cornell student can do just thay by putting his hand inside of one of Cornell’s three fistulated cows.

Cornell is one of several campuses that house to these fistulated or “hole-y” cows: cows sporting a three-inch cavity in their side. They can eat and digest just like any other cow and can even get pregnant and produce milk, but a team of Cornell veterinarians performed surgery on the adult cows and placed a three-inch circular opening in their rumens, one of a cow’s four stomach compartments. The veterinarians then inserted a soft rubbery plug called a cannula to close the opening, almost like a pierced ear with a plug in it. The cannula, made of plastisol, is not permanent and is replaced at least once a year, since it hardens over time.

A cow’s digestion is important to many industries, especially to the farmers and corporations that use cows to produce milk and other dairy products.

The human digestive system seems pretty straight forward compared to that of a cow. While humans have one stomach compartment, cows have a stomach with four compartments: the reticulum, rumen, omasum, and abomasum. The largest compartment is the rumen and is located on the left side of the cow, where the fistula was added in Cornell’s cows.

Within the rumen, there are many different types of bacteria that aid the cow in digesting plant fiber, like the pulp in citrus fruit, which humans and other non-herbivores cannot easily digest. The cows and the bacteria live in a symbiotic relationship in which both species benefit. The cows provide a warm home with plenty of glucose as food for the bacteria, and in return, the bacteria digest the otherwise indigestible plant fiber.

Cows are so dependent on these bacteria that if a cow becomes ill and the bacteria in its rumen begin dying off, there is a good chance the cow will die as well. The fistula provides easy access to a plentiful supply of replacement bacteria for any sick cow in danger of dying due to lack of its own natural bacteria. The bacteria can easily multiply and be transplanted from one cow to another. Not only does this eliminate suffering and death for many a sick cow, but it proves cost effective for dairy corporations and farmers.

The fistulated cows themselves don’t have it too bad either. Most of them actually live longer than the average cow, because they don’t get sent to the butcher or euthanized for not producing enough milk. Instead, Cornell’s three fistulated cows, named Holly, Violet and Rose, are free to roam in and out of their barn and occasionally have a researcher, group of elementary school children, or intrepid reporter poke their hand in their rumen in the name of science.