closing stock - horses

Client runs a stud breeding horses for sale as race horses. 

Closing stock consists of 15 horses, some racehorses, some broodmares, some foals.

I am reviewing the nrv against cost on a horse by horse basis.  Is that correct - i.e. you dont treat the group of horses as a class and compare cost and nrv in total?

Also, where the nrv is lower than cost, where do I post the difference to? is it treated as realised or unrealised?

Thanks