If you are new to colonies, I strongly suggest starting a bit smaller!
If you think it sounds easier than cage breeding, you have been misled. It's actually a lot more complicated, with less sure results.
Managing a colony can be a challenge for even very experienced rabbit breeders. While it is natural for rabbits to have access to each other, there is nothing natural about confining rabbits together.
Fights can turn brutal, and does can and do kill other does kits on occasion. I've seen some big nasty abscesses from "normal dominance behavior." I've seen kits die from hepatic coccidiosis, a protozoal disease picked up from contact with feces. Not fresh feces which is necessary for probiotics, but several-day-old feces.
Most people with successful colonies seem have the floors covered with something to help control waste. Concrete with barn lime and then bedding seems popular.
All vegetation is destroyed in short order.
Tractors can work, but I can't even imagine the labor involved with moving enough tractors to keep 70 rabbits clean and off their waste.
Here, any open topped pen would be a buffet for birds of prey, raccoons. and opossums.
__________ Thu Jan 26, 2017 12:41 am __________
I'm writing all that up from the perspective of someone who has tried colonies on and off for a few years. I had to find the right rabbits before I could make any real progress! The does I had before would fly out of their pens to pounce upon other does.
The harlis I keep now are more mellow, and I tend to cull hard for temperament.
One experiment was ended with disease and some very badly suffering kits.
Even with the few very docile animals I have now, babies are never born in the colony. The does are placed back in their big cages for kindling. This way, they do not get rebred right away, I can insure the nests are properly constructed and contain enough fur to keep kits warm, everyone's getting enough of the right nutrition, and no one is peed on or in contact with feces.
Also, because I cull hard for things like nesting ability, milk supply and mothering ability, it's kind of important to know how each does is managing with her litters.
Kits are only allowed on the ground after they are past at least 8 weeks old. This gets them past the most vulnerable age for coccidiosis.