Lameness whispers before it limps
The cheapest moment to catch sheep lameness is while it is still a whisper: a sheep whose stride shortens on one leg, whose head nods as the sore foot lands, who grazes kneeling on her front knees to spare her feet, or who keeps lying down and lags when the flock is moved. Watch the flock walking to fresh ground rather than standing in the pen - movement shows what standing hides. One mildly lame sheep is a job for today; whatever is brewing in her feet is easier and kinder to deal with now than as a stiff, non-weight-bearing case next week, and early attention protects the rest of the flock if infection is involved.
Turning her up and reading the foot
Catch her quietly and tip her onto her rump in the handling pen, working calmly - a stressed sheep kicks, and a kicked hand trims badly. Clean mud and muck away and look in sequence: between the toes for redness and soreness, under the edges of the horn for pockets where horn has separated and trapped dirt, and across the sole for lodged stones and thorns. Compare the sore foot with a sound one on the same sheep - the difference in shape and smell tells you more than any single view. Note which sheep and which foot before you start trimming, because you will want to find this exact foot again in a few days.
Trimming: take the horn, leave the foot
The aim of trimming is to restore the foot's natural shape, not to sculpt it. With clean, sharp foot shears, trim back loose and overgrown wall horn in small cuts, following the line a sound foot shows, and clear horn that has folded under and is trapping muck against the sole. Never pare the sole down thin and never cut into the pink, living tissue - if you see pink, you are done on that foot, and if you draw blood, stop, let the sheep rest, and make a note of it. Trim conservatively: you can take more horn next week, but you cannot put any back, and an over-trimmed sheep is lame on your work rather than on her problem.
When the answer is not the shears
Recheck trimmed sheep within a few days. A sheep no better after a careful trim, a foot hot and swollen up into the leg, a sheep off her food, or several sheep lame at once - that pattern has outgrown trimming and needs your vet's eyes, because flock-level lameness has causes that shears cannot fix. Keep lame sheep where you can reach them easily until they are sound, and keep your tools clean between animals when infection is in the picture. KinsLe's Care Teams lets you set the flock's regular foot checks as assigned duties and record each trim against the day it was done, so a sheep flagged on Monday is genuinely rechecked on Thursday rather than remembered about on Sunday.