Siegecraft Commander

Start a local multiplayer game on Crater's Valley as Human. Build a Garrison and a Hatchery. Fire a dragon in a direction so that it will pass over a cow. The dragon will automatically pick up the cow as it passes over it. The achievement will unlock a second or two later.

Very easy achievement once you have collected both resources, just find a cow, plant a hatchery and shoot the dragon over top the cow.

I also made a video for those of you who like to see it done.
(2:08)