From DF podcast:
Rainseeker: I just can't wait for us to have chickens.
Toady: Chickens and pigs, chickens and pigs and goats. Sheep and chicken and pigs and goats. Llamas, and sheeps and chicken pig goats and things.
Rainseeker: My dwarves are going to breed large chickens and they'll ride them into battle.
Toady: It's important to increase the size of the chicken.
Capntastic: The goat, not so much.
Toady: No the goat needs to retain the same size, whereas the chicken should be increasing in size, until it is as large as the goat, and then you breed the chicken and the goat, and then you get a chicken goat.
Capntastic: Game over.
Rainseeker: It's called a choak.
Toady: Yeah ... yeah ... that's right. It's okay ... Everything's just fine ...
Rainseeker: Until the cat sees the size of the chicken.
Toady: That's just not fair. Then you'll have to breed your cats to be the size of tigers.
Capntastic: A chicken eating a tin-can forever.
Rainseeker: Or in this case, discarded armour.
Toady: Well it'll solve all the refuse problems.
Rainseeker: It'd be cool if your goat ate your refuse. If it just ate anything, ate the rocks ...
Toady: Yeah you don't need miners anymore, you got a goat.
Capntastic: That's it, I'm quitting, I'm programming my own game: Goat Fortress.
Toady: That's right.
Rainseeker: Eats the mountain, eats it away.
Capntastic: You just have to be careful for bridges.
Rainseeker: Because of trolls!
Toady: That's right, that's why we get paid the big bucks.
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So yeah, it's planned.