There is no doubt that we have a problem with obesity in our horses nowadays, and it’s a battle for many owners to keep their horses at a healthy bodyweight. As for humans, there is great debate about how best to cause weight loss, and discussions can get quite emotive.

It is worth pausing to consider exactly why and how horses and ponies get too fat. Excess body fat is a direct consequence of excess intake of dietary energy. It’s simple physics. The law of conservation of energy is actually an empirical law of physics. Energy in an isolated system remains constant and can neither by created or destroyed – it can only be transformed from one state to another. The energy in feed that is not required for the body’s inner workings or for exercise is transformed into energy in body fat cells (adipocytes).

There are a number of factors that affect fat storage in horses and ponies, including breed type, appetite, genetics, environmental factors, and hormones but underlying all of these is dietary energy intake. Even a pony who is a very good doer cannot get too fat if they do not have access to excess dietary energy.

Only energy restriction (through reduced dietary energy and/or increased energy use via exercise) will cause fat loss in an overweight horse or pony.

Before we get totally negative about adipocytes, don’t forget that storage of excess dietary energy in body fat is an incredibly useful strategy, allowing a horse to survive a period of food shortage. Nowadays, however, most of our horses do not have a period of food shortage; hence they do not lose excess body fat they have gained from overfeeding or too much grass access.

The only way to reduce body fat in a horse or pony is to restrict energy either by decreasing input (dietary energy intake) and/or increasing output via exercise. The amount that is fed may not be relevant so simply restricting the amount of grazing or forage access may not be effective and could cause a welfare issue.

Horses and ponies will lay down fat stores if they have access to excess dietary energy from any source.

When faced with a horse or pony who needs to lose – or gain – weight (body fat) you must investigate and adjust the dietary energy intake. Assess the suitability of the forage and change if necessary, or soak hay for at least 12 hours to reduce energy content. Very few healthy horses or ponies will lose weight out at pasture 24/7 so grass intake will usually have to be restricted. Horses and ponies will develop health problems if left for long periods with nothing to eat so it is important to choose forages and feeds that are low enough in energy to be able to fulfil the horse’s innate need to chew and their digestive tract’s need for a trickle supply of feed.

Despite the physiology being more complicated than a simple statement, excess body fat is a result of excess dietary energy intake. Loss of body fat necessitates a dietary energy shortage so that the energy is extracted from fat stores, shrinking adipocytes. A basic fact, but one that can sometimes be lost in the great debate of the best weight loss strategies, diet feeds, different types of forage and management regimes.

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About Clare MacLeod

Clare MacLeod MSc RNutr is one of the UK’s few registered independent equine nutritionists who also has expertise in health and fitness. She advises private and commercial clients in all sectors of the horse world and is a hands-on horse owner herself. Clare is passionate about correct nutrition as a foundation for good health, without which peak fitness is not possible. She states “Good nutrition isn’t everything, but there’s nothing without it”.