This looks like an interesting pig tractor system, for low-tech areas (without electricity).
By Sebastian Scott, in Zambia
http://grassrootstrust.com/2014/03/new-pig-system/
And the short (one minute) video showing it in action
Even if the place for the pigs looks small (probably still better than in the industry), you can see that the tails are still there, and not munched on by the other pigs. Shows that they get adequate activity.
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