I tend to seperate all young off at weaning and keep them seperate, and any retianed lambs are kept with the flock. The lambs tend to go on fresh pasture / hay aftermath or rented 2-year ley, so no parasite issues.
I only worm If I have a problem / IE the weight gain dips bellow 200g/day avg when weighted every 4 weeks.
90% of my sheep never see click or crovect, - I cull militantly up and down bloodline when an animal gets ill.
A ewe gets foot rot twice, or struck once, Her daughters, mother and sisters are all removed from the flock.
I see little point in keeping freeloaders or spending money where it is not needed. The imrpvements are visible after just one year, and as you keep going the Sheeps welfare increases rapidly. Very much the idea behind the easycare sheep.