How Diet Affects Horse Behaviour and Temperament

Every horse owner has experienced it — you change your horse's feed and suddenly they're a different animal. Maybe they're spooking at shadows, jogging instead of walking, or becoming irritable in the stable. Or perhaps a dietary tweak has transformed a fizzy, anxious horse into a calm, willing partner.

This isn't coincidence. The link between diet and horse behaviour is well established in equine science, and understanding it can be one of the most powerful tools in your management toolkit. What goes into your horse's feed bucket has a direct and sometimes dramatic impact on their temperament, focus, and emotional state.

In this article, we'll explore exactly how diet affects horse behaviour, which feeds are most likely to cause problems, and what you can do to promote a calm, happy horse through nutrition.

The Science Behind Feed and Behaviour

To understand why diet influences behaviour, we need to look at what happens inside your horse's body when they eat different types of feed.

Blood Sugar and Energy Spikes

One of the most significant ways diet affects behaviour is through blood glucose levels. When a horse eats feeds high in starch and sugar — such as cereal grains like oats, barley, or maize — these are rapidly digested in the small intestine and cause a sharp rise in blood glucose.

This glucose spike triggers a surge of insulin, which in turn can affect the horse's energy levels, mood, and reactivity. Think of it like giving a child a bag of sweets — there's a burst of energy followed by a crash. In horses, this can manifest as:

• Excitability and fizzy behaviour
• Spookiness and over-reactivity
• Difficulty concentrating
• Restlessness in the stable
• Irritability when handled

Once the glucose is used up, the horse may then become lethargic or dull, creating an unpredictable cycle of highs and lows throughout the day.

The Gut-Brain Connection

Research increasingly points to the importance of the gut-brain axis in horses, just as in humans. The horse's hindgut is home to billions of microorganisms that play a crucial role not only in digestion but also in producing neurotransmitters and signalling molecules that influence mood and behaviour.

When the hindgut microbiome is disrupted — by sudden feed changes, too much starch reaching the hindgut, or insufficient fibre — it can lead to discomfort, low-grade pain, and changes in the chemical signals sent to the brain. A horse with poor gut health may become anxious, girthy, grumpy, or withdrawn, and we often blame their "personality" when the real issue is dietary.

Magnesium, B Vitamins, and Calming Nutrients

Certain micronutrients play direct roles in nervous system function. Magnesium, for example, is involved in nerve transmission and muscle relaxation. A horse deficient in magnesium may be more nervous, tense, and reactive than one with adequate levels.

B vitamins, particularly B1 (thiamine), are also linked to a healthy nervous system. While horses typically produce B vitamins through hindgut fermentation, disruptions to gut health can reduce this natural production, potentially contributing to anxiety and poor focus.

Common Dietary Causes of Behavioural Problems

Let's look at the specific dietary factors most likely to cause unwanted behaviour changes in horses.

Too Much Starch and Sugar

This is the number one dietary cause of fizzy, over-excitable behaviour. Cereal-based feeds — particularly those containing oats, barley, and maize — are high in non-structural carbohydrates (NSC). While working horses need energy, providing it in the form of starch and sugar often creates more problems than it solves.

As a general guideline, a horse's total diet should ideally contain less than 10-12% NSC for most leisure and light-work horses. For horses that are particularly sensitive, keeping starch and sugar even lower can make a noticeable difference.

Overfeeding for the Workload

One of the most common mistakes is feeding too much energy for the amount of work the horse actually does. A horse in light hacking that's receiving a competition-level hard feed is essentially being overfuelled. That excess energy has to go somewhere, and it usually comes out as unwanted behaviour — bucking, jogging, napping, or general tension.

Be honest about your horse's actual workload. Many leisure horses do perfectly well on good-quality forage with a balancer, and don't need a hard feed at all.

Insufficient Forage

Horses are designed to spend 16-18 hours a day eating fibrous forage. When forage is restricted — whether through limited turnout, small haynets, or long gaps between meals — it creates both physical and psychological stress.

Physically, an empty stomach means gastric acid splashes onto the unprotected upper portion of the stomach, potentially causing ulcers. Psychologically, a horse denied the opportunity to chew and forage becomes anxious and may develop stereotypic behaviours like cribbing, weaving, or box walking.

Fibre should always be the foundation of any horse's diet. It provides slow-release energy, supports healthy gut function, and satisfies the horse's deep-rooted need to chew.

Nutrient Deficiencies and Imbalances

Sometimes behavioural issues stem not from what you're feeding, but from what's missing. Key deficiencies that can affect behaviour include:

• Magnesium — linked to nervousness, muscle tension, and spookiness
• Vitamin E — important for neurological health; deficiency can cause anxiety and muscle problems
• Selenium — works alongside vitamin E; deficiency can affect mood and muscle function
• Omega-3 fatty acids — anti-inflammatory and thought to support a calm demeanour
• B vitamins — essential for nervous system function

If your horse is on a forage-only diet without a balancer or supplement, there's a good chance they're not getting everything they need. Analysing your horse's diet is one of the best first steps you can take to identify hidden gaps that could be driving behavioural issues.

Mycotoxins and Pasture Issues

Sometimes the problem isn't in the feed bucket at all. Mycotoxins — toxic compounds produced by moulds on hay, haylage, or pasture — can cause a range of symptoms including irritability, lethargy, and behavioural changes. Likewise, certain pasture grasses can accumulate high levels of fructans (a type of sugar) in specific conditions, particularly on sunny mornings after cold nights, which can cause both metabolic and behavioural issues.

How to Feed for a Calm, Focused Horse

Now that we understand the problems, let's talk solutions. Here's how to structure your horse's diet for the best possible behaviour and temperament.

Prioritise Fibre Above Everything

Make forage the cornerstone of the diet. Aim for a minimum of 1.5-2% of bodyweight in forage daily — that's 7.5-10 kg for a 500 kg horse. Where possible, allow ad-lib access to hay or haylage so your horse can eat little and often, as nature intended.

If your horse is overweight and forage needs to be restricted, use small-holed haynets, multiple feeding stations, and track systems to slow intake while still allowing continuous access to small amounts.

Choose Fibre and Oil-Based Feeds Over Cereals

If your horse needs more energy than forage alone provides, look for feeds based on digestible fibre sources (such as sugar beet, alfalfa, or soya hulls) and oil, rather than cereal grains. These provide slow-release energy without the blood sugar spikes.

Oil is particularly useful — it's energy-dense (roughly 2.5 times more energy per gram than cereals) but metabolised in a completely different way that doesn't affect blood sugar or behaviour. Adding a small amount of linseed oil or a specialised high-oil supplement can provide useful calories for harder-working horses without the fizz.

Feed a Balancer if the Workload is Low

For horses in light work, good doers, or those that maintain weight easily on forage alone, a feed balancer is often the ideal solution. Balancers provide essential vitamins, minerals, and amino acids in a small, low-calorie pellet — typically just 100-500g per day. This ensures your horse gets all the micronutrients they need without unnecessary calories or starch.

Support Gut Health

A healthy gut underpins calm behaviour. Support your horse's digestive system by:

• Making any feed changes gradually over 10-14 days
• Providing constant access to forage
• Feeding a prebiotic or probiotic supplement if your horse has a history of digestive issues
• Avoiding large starchy meals — if concentrates are necessary, split them into smaller feeds
• Ensuring access to clean, fresh water at all times

Consider Calming Supplements Wisely

The market is flooded with calming supplements, and while some have genuine merit, they're not a substitute for getting the basic diet right. Magnesium supplementation can help if your horse is genuinely deficient, and some owners report benefits from ingredients like tryptophan (a precursor to serotonin) or certain herbal blends.

However, before reaching for a supplement, make sure the fundamentals are in place: adequate forage, appropriate energy levels for the workload, and no major nutrient gaps.

Behaviour Changes to Watch For

Diet-related behavioural changes can be subtle or dramatic. Here are some signs that diet might be a contributing factor:

• Sudden increase in spookiness or reactivity — especially after a feed change
• Girthiness or grumpiness when tacked up — could indicate gastric discomfort
• Box walking, weaving, or cribbing — often linked to insufficient forage or gut discomfort
• Loss of focus during work — may relate to blood sugar fluctuations
• Aggression or irritability around feed time — can indicate pain, ulcers, or nutrient imbalances
• Lethargy and dullness — possibly linked to nutrient deficiencies or chronic low-grade pain

If you notice any of these signs, a dietary review should be one of the first things on your list — alongside a veterinary check to rule out underlying health issues.

It's Not Always Just Diet

While this article focuses on nutrition, it's important to acknowledge that behaviour is complex. Pain, dental issues, poorly fitting tack, training problems, turnout and social dynamics, and management all play significant roles. Diet is one piece of the puzzle — but it's an important one that's often overlooked or underestimated.

The best approach is a holistic one: address the diet, but also consider the horse's overall wellbeing, comfort, and lifestyle.

Key Takeaways

• Starch and sugar are the most common dietary causes of fizzy, reactive behaviour in horses
• Fibre should always be the foundation of the diet — it supports gut health, steady energy, and psychological wellbeing
• Nutrient deficiencies (especially magnesium, vitamin E, and B vitamins) can contribute to nervousness and anxiety
• Overfeeding for the workload is one of the most common mistakes horse owners make
• Gut health matters — a disrupted hindgut microbiome can send signals to the brain that affect mood and behaviour
• Slow-release energy sources like fibre and oil are far less likely to cause behavioural issues than cereal grains

Getting your horse's diet right won't just improve their physical health — it can genuinely transform their temperament and your relationship with them. Start by looking at what's going in the bucket, and you might be surprised at the difference it makes.