Why don herbivores, like cows, horses and sheep suffer from protein deficiency?
Many plants are protein-poor but herbivores eat a lot of them and utilize the protein that is there. Theoretically, you could be paid your wages in one-dollar bills and still have very good take-home pay. All animals produce their own proteins. If they ingest protein, they break it down to amino-acids and then re-assemble them into protein in the cells. Most carnivores do get vegetables in their diet from eating the stomach contents of the herbivores. The ones that don’t (such as vampire bats) get their nutrients second-hand and never seem to have any trouble.
