Livestock futures don't have "cost of carry" in the same sense as other non-biological commodities. The differentials between contract months are based on expectations of future supplies. If you "carry" livestock for too long of a period of time, the animals will gain too much weight and their meat quality will diminish. They'll no longer be suitable for delivery.
Thanx ......figure that there would be a storage cost associated with meats even if slaughtered, think a carcass could be frozen. Thanks again, J Law