Tipping the balance

Even forage and pasture can contribute to an excess of sugar and starch, triggering a cascade of health problems. David Rendle FRCVS offers dietary advice

-  David Rendle

HORSES evolved on pastures that were high in fibre and low in sugar and starch. As a result, they have adapted to meet most of their energy requirements by fermenting grasses and other plants to release the energy contained within the plants’ fibrous structure.

By harnessing the ability of bacteria to ferment fibre, horses are able to satisfy their nutritional needs through the ingestion of forage alone. With domestication, however, it has become commonplace to increase their energy intake through supplementation with feeds high in sugars and starches.

Feeding energy-dense cereals was more convenient and practical than large volumes of forage, particularly when horses worked long hours, under heavy loads, in urban environments. These days, only horses performing extreme levels of exercise require supplementary feeds high in sugar and starch.

Escalating levels of equine obesity demonstrate we are failing to balance energy requirements with feed. It is estimated that around 50% of horses in the UK are very overweight or obese.

When a horse’s energy intake exceeds what he requires to remain healthy and to exercise, the surplus is converted to fat. In addition to providing a means of storing energy, fat produces “signalling molecules” that alter the metabolism with the most notable change being a reduction in the responsiveness to insulin.

More insulin must then be produced to compensate, increasing the risk of laminitis. This combination of obesity, reduction in sensitivity to insulin and an increased laminitis risk has become known as equine metabolic syndrome (EMS).