The first truth is that nothing is lost in the universe. Matter turns into energy, energy turns into matter. A dead leaf turns into soil. A seed sprouts and becomes a new plant. Old solar systems disintegrate and turn into cosmic rays. We are born of our parents, our children are born of us.
We are the same as plants, as trees, as other people, as the rain that falls. We consist of that which is around us, we are the same as everything. If we destroy something around us, we destroy ourselves. If we cheat another, we cheat ourselves. Understanding this truth, the Buddha and his disciples never killed any animal. Link source