A zebra eats 10kg of grass How much of the energy contained originally in the grass usable by the loin?

Lions don't eat grass, so the question isn't applicable. Besides, this is just like the question asked about a cow eating so much grass and then asking how much of the energy from the grass can be usable by humans? It's immeasurable because food gets converted into energy in different ways for different animals, and to think that cutting out the middle-man would help bridge the gap between the energy lost is one that doesn't truly understand how it all really works. Humans aren't built nor meant to eat grass, nor are lions.