Cows + Grass = Herbivore Foregut Fermenters, and it's the very reason why cows do not need to be fed grain. Not even a little at milking time!
A cow eats grass to harvest TRILLIONS of microbial bacteria living on the blades of plants, which then ferments the GAZILLION itty bitty bacteria living inside her/his four section stomach, which perpetually goes through a mind-blowing frenzy of growth, division, multiplication (and eventually dying-off), but this symphony is also what converts the microbial bacteria into absorbable PROTEIN!
Cows ferment grass into protein! For themselves, and for us.
Cows need grass and only grass because of the native bacterial make up of their stomach, organs, muscle and tissue. It is why they have a four section stomach, and it is why cows do NOT need soy protein (nor corn etc), not even a little, at milking. The reason why a cow eats grass and needs only grass, is to provide a food source for her/his real meal — the bacteria! It’s the bacteria that breaks down the hard-to-digest cellulose of grass/plants, to then convert it into a plethora of different amino acids, which is the structure of all building blocks for creating a healthy 55LB baby calf, and then sustaining that calf magnificently well into a 850-975 LB milking cow.
When a cow chews grass, her/his saliva starts to open up the plant cells which are transported to chamber #1, the rumen. The rumen is laced with magnificent microbes inviting the grass, where it ferments beautifully in the dark, wet oxygen-starved anaerobic chamber (exactly like when I place organic cabbage in a barrel, which later gives me copious amounts of Vit C sauerkraut). The rumen returns (regurgitates) some of the grass back into the mouth, for further chewing (the cud).
The second & third chambers have entirely different microbes that search-for and drain off water and fatty acids, which separates and sends everything where it's supposed to go, into the fourth chamber where enzymes and acids ripen and further separate dead microbes, so that only the nutrients and protein can be then absorbed by the cow's intestines.
So Cows + Grass = Herbivore Foregut Fermenters. Cows brew (convert) grass into delicious protein and fat for themselves, and for us!
This is lovely magic. It has worked for cows (environment and people) for thousands of years, long before marketing boardrooms and corner-office accountants invented bagged feed for animals, stuffed with cheap soy and laced with unhealthy oils.
Cows are not 99% herbivores + 1% something else.
Cows are 100% herbivores, 24/7/365.
Cows don't stop preferring grass, at milking time.