Exiting the European Union

I used to have a farm in the Rhondda. One of the issues that I know is facing Welsh farmers in particular at the moment is that tupping has already happened for the spring flock. A pregnancy in a sheep takes roughly 152 days, so lots of commercial decisions have already been made by lots of farmers. How are they to proceed when they do not have the faintest idea what tariffs may or may not apply to Welsh lamb, 50% of which is sold in the rest of the European Union, on 1 January?