Why Horses Don’t Eat Percentages

When ensuring our horses receive a healthy and balanced diet it is important to consider
their Water-Soluble-Carbohydrate (WSC) intake. WSC are made up of sugars, starches and
fructans and if fed in excess these can cause problems like laminitis, especially for horses
with Insulin Dysregulation, Equine Metabolic Syndrome (EMS), and PPID (Cushings). It can be easy to fall into a trap of trying to select or avoid certain feeds or supplements based on the % of sugar and starch listed on the packaging. This is a trap because horses don’t eat %’s, they eat micro-grams, grams and kilograms. The maximum limit for WSC intake in ‘sugar’ sensitive horses is considered 1g per kg body weight per meal, so for an average 500kg horse we would want the WSC intake to be less than 500g.

To work out if a feed or supplement is a suitable option, both the % of WSC’s and the
amounts being fed need to be considered. This can be calculated by dividing the % of sugar and starch by 100, then multiplying this by the number of grams fed, per feed. This
calculates the total grams of sugar and starch, which then needs dividing by the horse’s
weight (kg) to calculate the grams of sugar and starch per Kg body weight.
Below are two examples, the first is a feed with 20% sugar and starch fed at 500g/day and a second is a feed with only 8% sugar and starch but fed at 2kg/day.

Example 1
20% sugar + starch
(20÷100) × 500 (g’s fed) = 100g total sugar & starch
100÷500 (kg weight of horse) = 0.2g per kg bodyweight.

Example 2
8% sugar + starch
(8÷100) × 2000 (g’s fed) = 160g total sugar & starch
100÷500 (kg weight of horse) = 0.32 per kg bodyweight.

While both are within the desired levels it is easy to see that the feed with the lowest
percentage of sugar and starch provides over one and a half times as much sugar and starch as the first feed, due to the difference in the amounts fed. In the case of supplements, the daily feeding rates are typically very low so their contribution to total dietary sugar and starch is usually minimal.

In summary horses don’t eat percentages, so percentages alone shouldn’t be used to choose or eliminate a feed or supplement. By avoiding a feed or supplement simply because of the sugar and starch percentage and not the actual intake, you could eliminate a perfectly suitable option for your horse.

Jennifer Little BSc Hons MSc RNutr PgCert PgCert
Equinutrition®

17th October 2025