Fat or muscle? A vet's guide to telling them apart under your hands

The facts

Source

Lucy Grieve MRCVS, ambulatory vet at Rossdales in Newmarket and a former President of BEVA, writing for Your Horse on 28 October 2026

Muscles in a horse

Around 700

Common fat sites

Crest, rump, over the withers and over the ribs

Health risks of excess fat

Laminitis and equine metabolic syndrome

Key test

Muscle contracts and relaxes; fat never does

A horse carries roughly 700 muscles, and every horse has the same ones in the same places. What varies is their size, which depends on how they are used, plus some breed-specific programming. Grieve explains that topline along the neck and back builds when a horse works in a correct outline, while a horse going hollow builds muscle underneath the neck and loses topline mass instead.

Fat is less tidy. It varies far more between individuals, though it tends to gather on the crest, the rump, over the withers and over the ribs. The practical difference you can feel is tone: muscle should feel firmer, tighten when it is under tension and wobble when relaxed. Fat cannot do either. Soft fat can also turn hard and lumpy when the tissue is over-filled, rippling as it moves. Muscle is denser and heavier, with collagen, blood vessels and nerves; fat is largely stored fat in cells with a blood supply and little else.

The part that catches owners out is what sits inside. Grieve notes that fat between the abdominal organs is sometimes laid down before a horse looks fat from the outside, so the first sign may simply be a slightly bigger abdomen. Only once those stores are saturated does visible fat appear. It also works the other way round: a horse that has lost its visible fat can still be carrying internal fat. Those full fat cells behave like an organ, releasing cytokines into the bloodstream that drive insulin dysregulation and, in turn, laminitis.

Weight gain has two different signatures. A horse without much fat that is being worked harder will gain slowly and subtly as it lays down muscle, much like a young horse developing after being broken in. A horse gaining through extra calories without extra work gains faster, and you will see and feel crest, shoulder, rib and rump fat, and may stop being able to find the ribs under the skin.

What this means for you

Owners of a good-doer

A flat stomach is not proof of a healthy weight. A slightly rounder abdomen can be the first sign, before any visible fat on the crest or rump.

Anyone dieting a horse

If the horse stays in work, muscle size should hold roughly steady, so the weight coming off is fat. Expect visible fat deposits to get smaller and softer.

Anyone body condition scoring

Looking is not enough. Grieve is clear that you need to feel the horse, and do it repeatedly over time, because the changes show up in the comparison.

Riders working on topline

How the horse goes decides where the muscle lands. Correct outline builds the top of the neck and back; a hollow outline builds the underside of the neck and costs you topline.

What to do

1. Run your hands over the crest, withers, ribs and rump and note what you find, rather than judging by eye from the gate

   This week

2. Press and feel for tone. Firm tissue that tightens under tension and wobbles when relaxed is muscle; tissue that does neither is fat

   Same session

3. Body condition score by hand and write it down, then repeat so you have something to compare against

   Repeat over coming weeks

4. Check whether you can still feel ribs under the skin, and treat losing them as a sign of fat gain rather than condition

   Ongoing

5. If visible fat has gone but you are still worried, talk to your vet about internal fat and laminitis risk rather than assuming the job is done

   Before spring grass