Crutching is an important part of the process. Here’s an explanation (it's a dirty job but someone's gotta do it)...
Crutching is shearing the wool from the rear end of a sheep – between the legs and around the tail. The purpose is to remove ‘dags’, which are clumps of wool stained with faeces and urine.
Sometimes the dags are just snipped away with hand shears. This is called ‘dagging’, a word you may have heard before on The Archers. But if more extensive treatment is required, then a farmer may call in the shearers. In this case, it’s a welcome bit of extra work for the newly-established 'Ambridge Shearers' Ed Grundy and Jazzer McCreary.
Both crutching and dagging reduce the chance of fly-strike. This is a nasty condition where flies lay their eggs in the wool, and the sheep itself becomes a meal for the fly larvae. Dags can also cause inflammation of the udder.
It's also beneficial at lambing time. While a new-born lamb has a very strong sucking instinct, it’s not very discriminatory. It can easily start sucking on a dag rather than one of its mother’s teats. So aside from the fact that the lamb won’t be feeding properly, the germs it swallows will make it ill, to the point of threatening its young life.