Actually, the elephants processing plant is way more complicated than ours. They essentially live of the bacteria that consume the trees and other plants they eat. On the other hand, one of the biggest critter, the Sperm Whale way bigger than the Pachyderm, eats meat. Lots of it. Simple digestive system, spurns sea weed.
I eat a ton of meat and dairy, but its perfectly possible to be a healthy vegan. http://www.fuelforthefighter.com/the-fighter/ theres a list of professional and very successful MMA fighters who are vegans Then in the NBA we have players like Wilson chandler, Al Jefferson, Garett Temple, Enes Kanter Kyrie Irvine and of course Damian Lillard. All Vegan. As far as Calcium, most leafy greens like Kale have a bunch. One cup of kale has 245mg of calcium while 1 cup of milk only has a tad bit more at 305mg per cup. Many fish like sardines, Veggies like Broccoli or Boy Choy, and nuts like almonds all have substantial calcium. All nutrients are fairly easy to get and plentiful on a vegan diet if you plan your diet and eat accordingly. Eating a crap-load of donuts might be vegan, but that's not healthy eating.