Anxious & Hot Behaviour

Most of us have seen the effect of excess energy causing “fizzy”, excitable, ‘hot’ behaviour. So, let’s take a closer look as to why this is so and what’s happening for the horse and in the gut. Firstly, feeds high in starch/sugar (starch + sugar = non-structural carbohydrate NSC) cause big swings in blood sugar and insulin levels and peaks and troughs in the energy levels. Second, low fibre, high starch diets are associated with increased acid production. This creates issues for the horse in regulating gut acidity. Excitable, irritable and abnormal behaviour can be caused by visceral discomfort (i.e. gut pain).

A pain in the stomach? After eating cereal-based feeds or meals (especially large ones – over 2kg per meal) the mixing of feed with saliva and gastric juices slows down, causing fermentation, increased acid and ulcers in the stomach. More than 1gram of starch/kg body weight per meal increases the risk of gastric ulcers. For a 400kg horse, this equates to around 900g of oats, 890g of steam-rolled or 700g of micronized barley, 625g of steam-rolled or 580g of micronized corn per meal. It is not just grains that contain starches and sugars and it is important to be aware that commercial feeds also contain starch and sugar (table 1) as does pasture.1,2

High starch feeds and meals easily overwhelm the capacity of the stomach and small intestine, increasing the activity of the gut and the speed at which the feed reaches the hind-gut. Dumping of partially digested and fermented feed, sugar and starch into the hind-gut provides ‘food’ for and increases multiplication of bacteria that rapidly ferment sugar and starch, which increases the acid levels in the hind-gut — this has been linked to anxiety and aggression, bed eating and wood chewing in horses. Meal-feeding instead of ‘trickle-feeding’ (i.e. constant access to hay or pasture) also affects gut function due to altered chewing and saliva production. Horses chew over 43,000 times a day when they have free access to hay – compared to only 10,000 times when meal-fed. Not only does this frustrate the horse’s natural desire to chew, but it also reduces the moistening of food with saliva. Saliva is alkaline and a natural buffer of stomach acid.

Consequently, large starchy meals may result in gut pain and discomfort, increased risk of stomach ulcers, gastric colic, irritability, restlessness and poor performance. Horses often wood-chew or crib-bite to stimulate additional saliva production. Many of these problems can be reduced and even prevented by mimicking the natural eating patterns of the ancestral horse i.e. providing constant access to a low-energy, high fibre diet. In summary, excitable, irritable or abnormal behaviour often stems from visceral discomfort (i.e. a pain in the gut!!) because meal feeding increases the amount of acid in the stomach, reduces saliva production and the amount of time the stomach is empty – leading to discomfort, ulceration and some forms of colic. Crib-biting horses are at higher risk of digestive problems.

Feeding plenty of fibre definitely helps horses gut and brain function – and so does feeding oils. Foals of pregnant mares fed high fibre, oil-enriched feeds, and foals fed high fibre-fat creep and weaning feed, were more relaxed, showed lower reactivity to a novel object (a slowly twirling golf umbrella) and increased confidence walking toward and investigating the umbrella – compared to those fed high sugar/starch feeds. They also spent less time walking away from people and passed handling tests with flying colours. Similar studies in adult horses have found that increasing the amount of fat in the feed from 3% to 10% for two months diminished their fear ‘startle’ response when exposed to a moving jack-in-the-box, and their resting blood cortisone (a stress hormone) was lower when they were on high oil diets. The attenuation of startle responses would increase rider safety as horses would be less likely to ‘spook’.

Fear reactions are tested by presenting horses with a surprising event. The ‘tarpaulin test’ assesses horses fear of novelty: a bucket with food is placed in a corner of a tarpaulin and the horse must walk across the tarpaulin in order to eat. In the ‘umbrella test’ - a colourful umbrella is abruptly opened 1 metre from horse’s head. This assesses the horse’s propensity to show fear reactions when faced with suddenness. The ‘duck test’ measures the horse’s propensity to exhibit fear reactions when faced with novelty and suddenness. For this test, feed is placed on a wooden tray and the horse is left eating on its own for 3 minutes. Then, a plastic motorized duck is put on the tray. It turns around and makes noise for 20 seconds.  

Fear-related reactions are physiological responses that prepare the horse to deal with danger.

Docility/calmness and willingness to work; stereotypic (repetitive) behaviour (crib-biting, weaving and wind-sucking); aggression; coprophagy (manure-eating); restlessness and excitability are decreased in horses on fat/fibre-rich diets. Stereotypies (found in 1-26% of domesticated and over 40% of captive wild horses) are misbehaviours or ‘stable vices’, including annoying habits such as wood-chewing, water-tipping, blanket pulling or refusal to be caught. They are thought to be a ‘coping’ mechanism to deal with stress, boredom or frustration. Social isolation is a higher risk factor than confinement – and nutrition and exercise factors compound the problems.

Other research has shown that horses with limited hay/roughage intake show increased ‘restless’ and ‘nervous’ behaviour – increasing their access to ad lib roughage made them ‘quieter’ and less aggressive. Studies on ‘fear’ responses demonstrate that horses on oil-enriched, high-fibre diets have reduced reactivity to sudden visual, acoustic and pressure stimuli, and lower blood cortisol levels and heart rates. When fed for several months, fat-fibre diets facilitate more stable blood glucose and insulin levels – and this has consequences for brain function. Serotonin is the ‘feel good’ brain chemical. In a study on Dutch Warmbloods, serotonin was higher three hours after feeding a high-fibre/oil diet compared to the same horses on a high starch/sugar diet. Reduced vitamin B and low magnesium also contribute to irritable, fidgety behaviour.

Head-shaking also comes under the umbrella of ‘hot’, irritable or excitable behaviour. Current understanding is that is induced by bright light or sharp sounds irritating nerves in the head and face (trigeminal nerve) which then cause nasal irritation ­– similar to photic sneeze syndrome in humans. The light or sound-induced head shake is a violent and irregular, snorting toss, compared to the more rhythmic traditional head bobbing or nodding seen as a classic stereotype. The horse may appear to be trying to scratch its nose on a foreleg or ground as it snorts, even at a trot or canter. It nearly always worsens under work and eases when the horse returns to quiet shady rest, so is easily assumed to be just a behavioural problem. Generally, light-induced head-shaking is seasonal, and ceases if dark goggles (sunglasses for our equine companions?) or sun-blocking face masks are used.

It’s easy to see ‘hot’ behaviour as naughtiness, bolshiness, wilfulness or stubbornness. But horses are often in fact reacting to situations that cause them anxiety, pain or fear. Such ‘avoidance’ behaviours include loading problems, resisting having tack put on, resisting moving away from their paddock, friends or stable, nippiness, reluctance to move forward, spooking or refusing at jumps. Or they arise from the horse’s natural motivation to maintain social contact (resulting in the horse making behavioural attempts to regain contact, such as spinning around, pulling back or refusing to move forward) and/or avoid situations that are unfamiliar, unexpected or pain inducing. From here these behaviours can develop into real ‘problems’ for owners. It’s so easy to misunderstand the origin of the behaviour – without an understanding of the cause, our attempts at addressing the behaviour can lead to increased anxiety, making it very, very important to investigate possible sources of pain or discomfort. Unusual or a change in behaviour is often the first sign of physical pain or disease. Change in appetite, prolonged or unprovoked anxious or agitated states are all examples of behaviours that arise from physical or emotional discomfort.

Aside from feeding changes, an accurate diagnosis of the cause is the next challenge. Each horse’s unique experiences and learning help map out how the behaviour has developed. Behavioural modification may involve social interaction and increased time spent ingesting forage. Problematic behaviours associated with frustration were more likely to be seen in horses where full social contact is thwarted, while time spent stabled is associated with increased risk of handling problems, aggression and oral/digestive problems, and pain linked to aggression and a reduction in positive responses in interactions with humans.

There are several ways to reduce some of these dietary causes of ‘hot’ behaviour. Using fibre and oil instead of grains and concentrates helps reduce the blood glucose and insulin fluctuations. In children, breakfast foods with a lower glycaemic index (i.e. less effect on blood glucose and insulin levels) are associated with improved performance in attention tasks - a comparable response in horses is calmer, less distractible behaviour. Fibre and oil-based diets also slow feed intake, stomach emptying rates, fermentation and acid-related discomfort. Likewise, they increase feelings of satiety and reduce frustration and the behavioural need to forage. Many of our day-to-day practices in looking after and caring for our horses involve important differences from the evolutionarily-determined way of the horse. There are significant changes in the type, quantity and frequency of feeding plus housing limitations that differ from the natural needs of horses. Meal-feeding and stabling place a limit on behaviours that are ‘normal’ for horses — grazing/browsing and foraging, moving, locomotion and social contact. Separating these behavioural needs from those of frustration, excess energy reserves or lack of stimulation is difficult.

As well as an understanding of the effect of diet on gut function and behaviour, we must be mindful of equine learning (ethology - the science of behaviour). Research on in free-living horses suggests that the majority of ‘problem’ behaviours occurring in horses are actually normal responses – but are problematic when they occur in certain circumstances. Consider – as a free-living, prey species, horses survived by reacting to uncertainty, novelty and danger by avoidance, i.e. running away. They are also highly social - this facilitated the detection of and escape from predators. Plus, they had a fairly poor diet, and spent most of their time grazing. These three evolutionarily-determined characteristics are behind much of the behaviour of modern horses as they try to avoid potential dangers, is providing us with more information on how to read a horse’s emotional state and this will help us differentiate between fear, pain and anxiety and with correct nutrition will increase our understanding and therefore our approach to ‘hot’ behaviour.

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