[devonlad]

Seems to be some confusion between slurry and FYM here.   
 Dairy slurry is liquid and provided ground is free draining will wash in fast.   Where and when they are spread is regulated in some areas to avoid pollution. 

Worms are not passed from cattle to sheep.  Other parasites/diseases can be)

Mainly true but dairy slurry is not completely liquid. I have walked many a field where remnants from slurty still lay visible several eeeks after application.  It is a hugely under valued source of nutrients but guidance about its best use are available on defra website for good reason.  To avoid pollution, and livestock health issues.