Your horse's large colon — the final section of the digestive tract — holds between 80 and 100 litres of fluid and digesting material. Roughly the contents of a large bathtub. In the context of endurance, that is not just a digestive structure: it is your horse's built-in water reservoir.
How the reservoir works
When your horse eats hay, the fibrous material moves into the large colon and holds water as it digests. The large colon is not a passive pipe — it actively manages fluid balance. As your horse sweats and loses water through breathing during a long ride, the body draws on this internal reservoir to help maintain circulation and hydration.
Think of it this way: a hay-fed horse starts the ride with a full water bottle built into its body. The fibrous gut contents release fluid gradually — not all at once, but steadily, across the hours of a ride. A horse whose large colon is partially empty starts with a smaller reservoir, reaches dehydration sooner, and needs more water from external sources (drinking at the vet gate) to compensate.
Remember
Every hour without hay reduces the large colon's fluid reservoir. A horse that starts an endurance ride with a full large colon is better placed to manage fluid losses than one held off hay 'to make it lighter'. The weight of a full large colon is not dead weight — it is a survival advantage.
The 'lighter horse' misconception
This is one of the most common — and most damaging — misconceptions in endurance management: 'if I restrict hay before the ride, my horse will be lighter and go faster'. The logic seems to add up: less gut fill = less weight = faster horse. But that reasoning does not survive 80 or 160 kilometres.
A horse with a depleted large colon reaches dehydration sooner, is more likely to fail the cardiac recovery inspection (CRI) at the vet gate, is at greater risk of reduced gut motility (grounds for elimination), and often performs worse in the second half of the ride. The small benefit of a marginally lighter horse at the start is vastly outweighed by the risks of reduced fluid reserves across the full distance.
What this means in practice
- Hay available freely until 1–2 hours before the start — no overnight or morning restriction except that short window.
- Hay or alfalfa chaff at every vet gate — before electrolytes, before concentrate, and before anything else except cooling and water.
- Hay freely available from immediately after the finish throughout recovery.
Gut sounds at the vet gate
Gut sounds are assessed at every vet gate inspection. A horse with absent gut sounds may be eliminated. The most common cause of reduced gut sounds is not illness — it is insufficient forage intake before and during the ride. Hay prevents this.
This is general information. It does not replace the individual feeding plan your EVN vet prepares for your horse after assessing it.