Written by: Sam Potter (BSc(Hons), MPhilVSc (Equine Nutrition)

The days of locking horses up in the ‘Jenny Craig’ paddock – with minimal feed to achieve weight loss – are gone. We now know that this puts horses at serious risk of other health issues such as gastric ulcers and colic.

Nowadays, there’s a better way – and it’s by reducing energy (calorie) intake rather than reducing feed intake altogether. The principle behind feeding for weight loss is based on replacing higher energy pasture or hay in the diet with lower energy hay or straw (in sufficient quantities) and at the same time ensuring protein, vitamin and mineral requirements are met. This approach results in a much healthier horse, which is more likely to lose weight.

Why control weight?

Just like in humans, overweight horses are more prone to serious health issues – and in horses these issues include potentially life-threatening problems such as laminitis. Excess weight also places increased pressure on your horse’s bones and joints. And if your horse is too fat, they are much more likely to suffer from heat stress in hot weather.      

Why do some horses become overweight?

Some horses just need less energy in their diet than others to maintain the same weight. We call horses that are prone to tubbiness ‘easy keepers’ or ‘good doers’ and genetics plays a major role in determining this.  

But of course, what – and how much – your horse eats, also affects their weight (This is also the part we can control). Horses get too fat when their feed provides them with more energy (calories) each day than they use. The spare energy is stored as fat. In a natural situation, this mechanism helps horses survive poor seasons. When there isn’t good grazing and the pasture can’t provide as much energy each day as the horse needs, their fat reserves give them the extra energy required.

That’s in the wild. Domesticated horses on the other hand, typically have access to higher energy pasture and hay species, and they do less free exercise because they are kept in smaller paddocks. It’s also less common for domesticated horses to go through periods of the year where their diet doesn’t meet their daily energy needs – so there’s no natural, seasonal opportunity to lose weight. Year after year, their body weight increases ever-so-slightly and before you know it, you have a fat horse.

So what can you do if your horse is getting a little rotund?  

Restrict pasture intake

Unrestricted access to pasture is often the biggest cause of horses getting too fat – particularly where the pasture is of high quality. For easy keepers, pasture intake alone can provide more energy than your horse will use each day (as shown in Figure 1).

Figure 1- Using FeedXL Nutrition Software to demonstrate, unrestricted access to an excellent quality mixed grass pasture (typical of Spring pasture) provides far more energy (130% of daily requirement) than this easy keeper needs. 

There are many benefits to keeping your horse on pasture, including free exercise, ability to be with herd mates, general contentedness – not to mention how good pasture can be nutritionally. So, we don’t necessarily want to stop pasture access altogether. Rather, the aim is to reduce the amount of pasture your horse eats when they’re given pasture access.

The other point to note here is that restricting pasture intake might also only be necessary at certain times of year – usually when pasture is of excellent quality, ie. when it is green, growing and predominantly leafy.

So, how do you restrict pasture intake effectively? There are a few options:

Strip grazing involves fencing off a small strip (10-20 m wide) in your horse’s pasture using a portable electric fence. The fence is moved daily to allocate a fresh strip of pasture to graze. Ideally a lead (front) fence and a back fence are used to prevent horses having access to the previously grazed strips (which also has the benefit of allowing your pasture to ‘rest’ and regrow before the next grazing).

Strip grazing has been shown to reduce pasture intake in ponies by 20-30% compared with ponies who were given unrestricted access to pasture. This is the equivalent of your horse eating 130% of its energy needs if given unrestricted access, and reducing this to 90% of its energy needs by using strip grazing (see Figure 2). Or to put it another way, it equates to reducing pasture intake from ~7kg (dry matter basis) per day, down to ~4.9kg (dry matter basis) per day.

Note: In this scenario it would also be recommended to provide some low NSC hay to ensure forage needs are met.

Figure 2- Example of how energy intake is effectively reduced from 130% with unrestricted access (as shown in Figure 1) to 90% using strip grazing to reduce pasture intake.

A grazing muzzle is a device fitted over the horse’s head and mouth which means they can eat some grass with it on, but not nearly as much as they would with it off.

A grazing muzzle can reduce pasture intake by as much as 50-80% per day. The amount intake is reduced by will depend on the type of muzzle you use and how well your horse adapts to grazing with it on.  A reduction in pasture intake of 50%, reduces energy intake from 130% to 54% of daily requirements (see Figure 3).

Note: Again, in this scenario it would also be recommended to provide some low NSC hay to ensure forage needs are met.

Figure 3- Example of how energy intake is effectively reduced from 130% with unrestricted access (as shown in Figure 1) to 54% using a grazing muzzle to reduce pasture intake.

Restricted turnout time. For most horses, this isn’t as effective as the two methods above, because horses quickly learn to ‘gorge’ themselves (particularly ponies) and eat nearly an entire day’s pasture intake in just a few hours. Restricted turnout time is a strategy that is best used in conjunction with strip grazing or a grazing muzzle to effectively reduce intake.

Note: Low NSC hay should be provided at the times when the horse or pony does not have access to pasture.    

Feeding low energy hay and straw

It’s important to remember the aim in all this – we want the horse to lose weight by replacing higher energy forage (pasture or hay) with low energy forage – rather than by restricting forage intake per se. So, if you’re using methods like strip grazing, a grazing muzzle or restricted turnout time to reduce pasture intake, it’s important to make sure that your horse still gets enough other forage to maintain a healthy gut and avoid complications like gastric ulcers and colic.

Low energy forages such as mature, stalky grass hay or straw are the most suitable options as they provide forage/bulk, but not too much energy. You’ll need to work out how much low energy hay/straw to give your horse to meet their daily feed intake. Around 2% of your horse’s body weight (7kg for a 350kg pony) is the minimum amount of feed you need to provide each day. This will take some guesswork but here is a guide, depending on which method you choose:

1. Strip grazing - Intake is reduced by approx. 30%. So, for a 350kg pony, this means pasture intake will be reduced from 7kg to 4.9kg per day. Therefore, to meet this pony’s forage intake we need to provide at least 2.1kg of hay per day.
    
2. Grazing muzzles - If pasture intake is reduced by 50%, the pasture intake would be 3.5kg per day. Therefore, to meet your pony’s intake needs of 2% of body weight (7kg per day), we need to provide 3.5kg of hay each day.
    
3. Restricted turnout time – This is trickier to estimate as pasture intake will vary depending on the horse, how much they ‘gorge’ themselves and time allowed on pasture. But for many overweight horses, 1-3 hours turned out on pasture each day is common. In this case, pasture intake is possibly reduced by as much as 80%, which equates to just 1.5kg per day. This means that when the pony isn’t turned out on pasture, you need to provide at least 5.5kg of hay to meet feed intake requirements.      

A Balanced Diet

As with any horse, providing a diet that supplies adequate protein, vitamins and minerals is essential to overall good health. For horses who have access to some green pasture, protein requirements are likely to be met – so the diet can be balanced by simply adding a good quality vitamin and mineral supplement, such as Digestive VM.

To give you an idea of what a well-balanced diet looks like, the following are examples for a 350kg overweight pony:

Example 1 – Strip Grazing

• Restricted pasture intake
• 2kg low energy hay or straw
• 250g Lucerne Chaff or 100g Beet Pulp
• 40g Digestive VM  
• 90g Digestive EQ
• Free access to salt lick

Example 2 - Wearing a grazing muzzle for 10-12 hours per day

• Restricted pasture intake
• 5kg low energy hay or straw
• 250g Lucerne Chaff or 100g Beet Pulp
• 40g Digestive VM  
• 90g Digestive EQ
• Free access to salt lick

Example 3 – 3 hours turnout per day

• Restricted pasture intake
• 5kg low energy hay
• 250g Lucerne Chaff or 100g Beet Pulp
• 40g Digestive VM  
• 90g Digestive EQ
• Free access to salt lick

The role of exercise

Exercise increases the amount of energy your horse uses each day, which uses up more of the energy provided by the diet, and further encourages weight loss. If your horse or pony is sound and otherwise healthy, trotting for at least 30 minutes 3-5 days per week is recommended.   

How do you measure weight loss?

There are a few methods. You can make ‘body condition scoring’ (BCS) assessments, but in my studies on this topic, owners frequently underestimated BCS by at least 1 score (ie. they thought that the horse looked thinner than it actually was). Owners also often struggled to see small changes in BCS and could lose faith in the weight-loss regime (even though their horse was actually losing weight). So, recording measurements with a tape measure is a much better and more objective bet for monitoring weight loss in your horse.

You can use a long measuring tape, but a weight tape is also ideal to make your measurements – neck, girth and belly circumference – purely because it’s long enough. You can also use the actual weight tape part to estimate body weight, but you really need to measure all three sites (recorded in cm) to get an accurate picture of weight loss.

Most overweight horses tend to be ‘cresty’ so measuring their neck circumference is important. The girth and belly measurements show changes in fat cover over the ribs. Surprisingly, the ‘heart girth’ measurement (the location where you would traditionally use a weight tape) shows the least changes during weight loss – changes in this area mostly account for the fat pad over shoulder. So, all three measurements are needed.

To start measuring for yourself, take a look at Figure 4 to see exactly where measurements should be taken.

Measure these at the start of your horse’s weight loss journey and do it again every 4 weeks (and write the results down in your phone or in a book) to monitor their progress.

Once you have these measurements you should also reassess the diet each month and decide if continued pasture restriction (and substitution with low energy hay) is still required to achieve the desired weight loss.

Weight loss takes time

Be patient and keep the faith. Achieving weight loss in a safe manner is slow. It can take 3-5 months for a horse on a restricted energy diet to reach a healthy weight; sometimes it takes even longer. It’s worth persisting.

Most importantly please don’t be tempted to lock your tubby horse in the ‘Jenny Craig’ paddock with minimal feed. It sounds dramatic, but this approach is a recipe for health problems and avoidable unhappiness. Whilst it may result in weight loss, starving the weight off your beloved horse or pony places them at risk of gastric ulcers, colic and can compromise their overall health.

Instead, replacing higher energy pasture or hay with adequate lower energy hay or straw, and ensuring that protein, vitamin and mineral requirements are met, are all essential for achieving weight loss in a safe and healthy manner.  

Good luck, and as always, get in touch if you need a hand.