Also, they use eggs and milk, so we know they’re not vegan.

@Background Pony #EDF5  
Applejack keeps pigs. They’re not sapient, they don’t seem to be pets, and they don’t produce milk or wool… so why keep them?
 
There’s evidence for both sides of the debate, and I doubt we’ll ever see absolute canon confirmation one way or another.

Or, it’s soy!

It’s false meat like what vegetarians and vegans eat.

@Ridley Wolf  
Pinkie explicitly stating they are all vegetarians is a pretty good reason.

I’m surprised this image didn’t disintegrate when you blew the dust and cobwebs off it.

A lot of horses will eat meat if they can get it. I see no reason to believe ponies are any different.