Here are two pages to help you calculate how many head of cattle a farm would need need to support recommended manure rates at 20 tons per acre. Don't forget to divide days and nights because manure in the field isn't collected far as I know, only the dung in the barn.

http://www.uvm.edu/vtvegandberry/factsheets/managingNorganic.html

http://www.extension.umn.edu/distribution/cropsystems/DC5882.html

My calculation comes to roughly 200-280 good size half-grown or full grown head of cattle needed to self-sustain the manure needs of just a 50 acre farm, assuming the cattle are out most of the day in summer, and housed a good part of the day in winter.

That, is one really really big barn, and one really really big free range pasture. The garden part of this business is going to be quite a minor part of it. Looks more like a major cattle ranch with a small garden attached.

Here are a couple pages to help you calculate your stocking rates per acre of cattle. You are talking about a very very large ranch to support just 50 acres of farm, about 800-1000 acres at minimum.

http://www.cattletoday.com/forum/about1979.html

http://ohioline.osu.edu/b872/b872_18.html

More is going on here than meets the eye I'd say, and attempting to ruin the reputation of small organic farmers with claims of 'bio-dynamic' superiority is a disservice to us all.