[Ray]

1. There is no way on God's green earth I'm going to have piles of sh*t in my greenhouse.
2. That would also be somewhat less pleasant when the plants came into bloom and I wanted to take them into my display area in my kitchen.
3. Such a method may be "wholesome", but it is unsanitary. It's certainly not "natural" for plants to grow in it - except maybe those magic mushrooms I remember from college days. Oh wait. They're a fungus, not a plant. (Yes, I know - growing in clay pellets ain't natural either.)
4. There is no way to control the level of nutrition the plant is getting.
5. The nutrition provided by dung is incomplete, as well.
6. Andrew's point about a better liquid fertilization regimen is right on. In semi-hydroponics, in which established plants simply cannot be overwatered, I will sometimes feed and water them 5 or more times a week (I'm really going after the "mounties", but they all get it simultaneously). The result: larger plants with more leaves, more frequent flowering with more- and bigger blossoms.

To sum it up: When horses or cows fly and leave deposits in trees, and we learn that orchids do so much better because of that, then I might reconsider.