Build the check into something you already do
A separate daily inspection is a chore that gets skipped; a check folded into grooming happens forever. Pick the moment when he is tied up and standing quietly, brushes in hand, and run the whole routine before you start with the body brush. It takes two minutes once your hands know the route. Going in the same order every day — near fore, near hind, off hind, off fore, then the body — means you never have to wonder whether you did the off-side cannon or only think you did.
Legs: compare pairs, feel for heat and filling
Stand facing the leg and run both palms down it together, over the knee or hock, down the cannon, around the fetlock and into the pastern. You are feeling for three things: heat that one leg has and its pair does not, filling or puffiness that softens the clean lines of tendons and joints, and any swelling that pits slightly when you press a fingertip into it. Compare every finding against the opposite leg before you worry about it; symmetry is reassuring, and a one-sided hot, filled leg is a finding. Run a thumb down the back of the cannon where the tendons lie, and feel inside the fetlock and heel bulbs where mud and small cuts hide. Finish the leg by picking the foot out, which also puts your hand on the hoof wall, where unusual warmth is another early warning worth noticing.
The body sweep: learn his existing lumps
With flat palms, sweep over the neck, shoulders, back, girth area, belly and quarters, pressing firmly enough to feel what lies under a thick coat. Most adult horses carry a small collection of old lumps: scar tissue from a long-forgotten kick, a sarcoid that has sat unchanged for years, a wart-like knot in the mane line. None of these matters until it changes, and you can only spot change if you know the starting point. Pay particular attention to the girth area and under the saddle patch, where a new lump will be rubbed by tack, and to the face and jaw, where teeth problems and swellings announce themselves early.
Map what you find, in plain words
For each existing lump, record where it sits, its rough size against a coin, whether it is hard or soft, attached or movable under the skin, and whether the skin over it is normal. Add a phone photograph with your hand beside it for scale. Update the note whenever a lump grows, shrinks, changes texture or breaks the skin. This sounds fussy until the day you tell a vet 'it has doubled since March' and can prove it instead of arguing with your own memory.
Changes that shorten the timeline
Ring the vet promptly about a leg that is hot, swollen and lame, about heat paired with a strong bounding pulse in the foot, and about any swelling that arrives with a temperature or a horse who has gone off his hay. A lump that grows quickly, ulcerates, starts to bother him under tack or appears suddenly in a cluster deserves a booked appointment rather than monitoring. A cut near a joint, however small, is a same-day call, because joint infections move faster than owners expect. Keeping the dated lump map and daily notes inside his KinsLe Pet Passport means the vet reads the history of the change, not just today's snapshot, when she examines him.