How do animals with mostly vegetarian diets have so much muscle mass?

Question

Pretty much as the question states: How is it that animals that consume mostly vegetation as opposed to meat so strong?
More specifically, how are animals like gorillas and horses so strong/decked out with so much muscle mass if they primarily eat grass/hay (in the case of horses) or leaves and bananas and bugs (in the case of gorillas? I understand that certain animals metabolize (break down and use) different foods differently, but it’s just mind blowing to me that these animals have such large muscles on such vegetable-heavy diets.
Moreover, they’re able to gain and maintain this muscle mass on these lean diets while also using those muscles almost ALL OF THE TIME. I mean, it would be difficult enough for a human to achieve such a muscle mass eating that same type of diet, but I would imagine that it would be EXTREMELY difficult for humans to achieve and maintain that level of muscle mass while simultaneously burning so many calories each day by using those muscles – I would imagine that a human with a similar diet with that amount of physical activity and that kind of diet would be fit and muscular, but have more of a “lean” or
“slim” muscular build instead of looking jacked like a horse or a gorilla.
So, what gives? How are they able to be so strong on such vegetable-heavy diets?

In: Biology

Answer 1

Grass is between 15 – 25% protein and ~45% carbohydrates, depending on growing conditions. For reference, both cows and you are made up of ~22% protein, so some grass will actually have a higher protein content than meat does.

The reason that cows can eat protein but you can’t is because the main carbohydrate in grass is cellophane – the same stuff that plastic wrap is made out of. You can’t digest cellophane, and most of the protein in grass is coated in it. Because you can’t digest the cellophane, grass passes through your digestive tract in the same way that a piece of meat wrapped in cellophane would.

Cows can eat grass because cows can break cellophane down into sugar. Once the cow’s stomach has broken down the cellophane in the grass its eaten, everything else in that grass is easily digested.