Not treating or 'not seeing'You’re right, those with scab should dip their ewes. Not treating infested sheep is what spreads it around, not the non-treatment of sheep that are isolated from others, closed flocks, etc.
Or the best one "I used cydectin to sort the lice problem and dysect to sort the ones with scab, but not all of them needed treating so I didn't do them all"
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Maybe training on such matters should be mandatory for farmers to sell sheep to other farmers.
Or maybe a licence to keep animals [emoji848][emoji6]