The topic of reducing stress and calming our equine friends continues to be high on the conversation mill. This week, Dr Stewart revisits some nutritional factors involved and some of the latest research using minerals.
Most of us have seen and experienced the effects of ‘fizzy’, excitable, ‘hot’ behaviour – in a whole range of situations. Research 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. As a free-living, prey species, horses survived by reacting to uncertainty, novelty and danger by avoidance, ie running away. Horses 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 — and the presence of undiagnosed pain — are behind much of the behaviour of modern horses as they try to avoid potential dangers.
It’s easy to interpret ‘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. They can also result 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.
Let’s take a closer look at what the problem(s) could be. Firstly, feeds high in starch/sugar (starch + sugar = non-structural carbohydrate NSC) cause big swings and peaks and troughs in gut hormones, blood sugar and insulin level. 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) – literally a ‘pain in the stomach’ for horses, trainers, riders and owners!
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. 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.
Constant access to of fibre definitely helps horses gut and brain function – and so does feeding oils. Mares and foals fed high fibre-fat 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’. In adult horses 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. 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 B1 and low magnesium also contribute to irritable, fidgety behaviour. Anecdotal reports on the benefits of magnesium and thiamine have recently be validated in several university veterinary studies in Australia and Canada. In a ‘speed-reaction test’ (the time taken for a horse to cover 2 m in a custom-built chute after being startled), horses on daily magnesium supplementation were less reactive than when on acepromazine! This is the first time an objective measurement of behavioural change due to oral magnesium supplementation has been reported in the horse.
The Canadian study published in 2017, looked at the amount of stress horses experienced (in terms of heart rates and cortisol levels) performing a set task when they received either ACE or a magnesium-thiamine supplement. Heart rate was significantly lower when the horses received ACE or magnesium-thiamine, compared to when they were unsupplemented. The primary active in the study was magnesium with supporting bioactivity from thiamine. Magnesium is required for conversion of thiamine into its active form and a magnesium deficiency could potentially induce a secondary thiamine deficiency. This is one of the reasons we formulated EzyMag+!
Studies on tryptophan as a calmative are inconclusive, with one study in 1994 showing that doses of 0.05 and 0.1 mg/kg bodyweight increased both heart rate and activity under both isolation and visual contact environments — suggesting that oral tryptophan may stimulate horses 2–4 h after dosing rather than having a sedative effect.* A more recent 2017 study found the desired effects of tryptophan lasted only a few hours after administration and that longer term use may provide no additional benefit or may even have unwanted effects.**
Ongoing, ground-breaking research 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. Many behavioural issues are thought to be ‘coping’ mechanisms to deal with stress, boredom or frustration. So, in addition to ensuring magnesium and thiamine deficiencies aren’t occurring, go through the environment and your management to see if anything could be causing stress – including thwarting of psychological needs. We must be mindful of equine learning (ethology - the science of behaviour).
EQUINE CLINICAL NUTRITION
Dr Jennifer Stewart