Your hands find it weeks before your eyes do
A horse loses condition from the inside of the silhouette outward, and a camera — or a glance across the field — will usually miss the first fortnight of it, especially under a winter coat or a rug. Your hands will not. Make a habit of running them over the horse once a week in the same order: along the ribs, where you should feel them under a smooth covering rather than either not at all or with every rib distinct; over the topline, where the flesh either side of the spine should feel filled and level rather than dipping into a gutter; and across the hindquarters, where muscle should round away from the hip bones rather than falling away behind them. Compared against last week's feel, this is the most sensitive condition monitor you own.
The tack and rug tell the same story
Equipment fitted to the horse's body quietly records its changes. Girth holes are the classic measure: a horse who has done up on the third hole all season and now fastens easily on the fifth is telling you his barrel has shrunk. A rug that starts to slip sideways, sit low behind the withers or hang loosely over the shoulders, and a saddle that begins to bridge or rock where it sat still before, all say the same thing. None of these is proof on its own — rugs stretch and girths soften — but when the tack, the rug and your hands all point the same way in the same fortnight, the horse is losing condition and the question becomes why.
Appetite, coat and droppings: the supporting evidence
Watch how the horse meets his feed. A horse who starts leaving the end of his bucket feed, takes noticeably longer over hay he used to polish off, drops partly chewed feed, or plays with his water is giving you information — dental discomfort is one of the commonest reasons an older horse quietly loses ground, and it announces itself at the feed bucket before it shows on the ribs. The coat is a slower signal: a loss of shine and a staring, dull look to hair that was sleek last month supports what your hands found. Droppings changing in number, consistency or undigested content add another piece, particularly if the change is persistent rather than a single day after a feed change.
The weight tape turns feelings into a trend
Suspicion is not enough to act on well, so anchor it: use a weight tape on the same day each week, in the same position, and write the figure down rather than trusting memory. One low reading means little — gut fill varies — but three consecutive weeks drifting downward, or a sudden large drop, is evidence you can hand a vet, and it distinguishes a horse who is genuinely slipping from one who simply looks different under a new clip or after a wet week.
When slipping condition needs the vet promptly
Slow, small drift in a horse whose management has changed — a harder workload, a move to poorer grazing — may be answered by adjusting the ration and re-checking. But weight loss that continues despite adequate feed, or that arrives with reduced appetite, dullness, changed droppings, quidding, or a horse who is simply not himself, should go to the vet promptly rather than after another month of watching: the list of causes runs from teeth through gut and organ problems, and most of them are far easier to address at the stage your hands first detected than a season later.
The weekly habit only pays off if the readings survive to be compared, so keep them together — tape figures, condition notes, dental and worming dates and what was changed in the feed. Keeping those records together in the KinsLe Pet Passport means the vet's first question about how fast this has happened gets answered with a written trend instead of a guess.