If they have come from rubbish pasture onto good stuff they will get a bit loose - I take it is green stuff coming out?
I would offer some hay, ideally bring them into a pen for the night so they will eat some hay for a few nights until their systems have acclimatised.
I have just had a good look at mine, I think no flushing necessary this year
, especially the ones that didn't lamb thanks to tuppy being not quite up to scratch in the fertility department... but even the ones with lambs still at foot now do look quite good.