I drive by several fields of horses on my way to/from work, and i’ve always wondered… how to they they get that muscular with no protein? Sure owned horses might get a special feed that isn’t just grass, but wild horses don’t have access to that. As far as I’m aware, they just eat grass. Maybe the occasional fruit if they stumble upon one. Seems like an extremely low-nutrient, low-calorie, low-protein food for such a massive, muscular animal.
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As was mentioned, hay (and fresh grass/fodder) does have protein. The trick is the volume they eat. Cows need 3% of their body weight in food daily and horses even a little more if they are exercising much: Horses are eating (and crapping) machines. That means a 1500 pound horse is going to eat about 45 lbs a day (roughly half a small rectangular bail of hay or the fresh equivalent)
In terms of hay, it’s cut at what’s called the “Boot stage”. That is where it has started to make the seed blooms but hasn’t actually bloomed yet. The reason that stage is chosen is because protein is highest. Previous, the plant is putting energy into roots, leaves and stems. At boot, it’s put energy into the early stage reproductive organs (flowers basically) and since reproduction is the goal, they pump a lot of good energy at that. Past boot and to actual bloom/seed heads, the plant has sort of burned itself out and overall protein drops.
On a side note, ruminants like horses and cows don’t live fully off what they eat. Their stomaches are basically internal compost heaps where food rots through bacterial action. The bacteria bloom not unlike yeast rising bread or yogurt culture–so ruminants “eat” the high protein bacteria that is eating the compost in their guts. This is why those urban cows in India can survive eating nothing but near-zero food value cardboard: They are actually eating the bacteria and it’s by-products composting the cardboard in their guts.
FYI the heat generated by that internal composting feature is also what keeps them warm in cold winter temperatures. Most ruminants don’t need blankets in even extremely cold weather because that effective wood-stove in their belly does a great job.
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