I'm not well up at all on the new scheme however after reading your question and doing a bit of research it appears that the stocking rate for sheep is a lowland mountain ewe (I presume they mean lowland or mountain ewe) and her lamb. You can see from the attached DAFM link "Stocking Rate Calculator" - ** Nitrates figure used is for lowland mountain ewe and lamb.
Don't take my word on it - best check with your Ag advisor.