[SallyintNorth]

Veterinary advice is to not trim feet at all if you possibly can. 

As to eradicating it... mark the ewes whose feet you have to attend to; anyone with two or more marks, do not keep her ewe lambs on for breeders.  Once no-one has two marks, start not keeping ewe lambs from anyone with any marks.

Also some dry / hard ground they can use, when it’s not too soggy spread lime around water troughs,