Equine nutritionist LARISSA BILSTON, BAgrSc (Hons 1), Nutritionist, Farmalogic explains why nutrition can influence hot or anxious behaviour and what you can do to minimise the problem.
As prey animals, horses are naturally perceptive to potential dangers and will prime themselves for flight instinctively. An individual horse’s tendency towards ‘hot’ or ‘anxious’ behaviour is influenced by breed and genetics, life experience and training as well as the type and amount of feed ingested. Identifying which of several possible diet-related causes of altered behaviour is a critical first stage in determining the best nutritional strategy for long-term management of an individual horse’s health and behaviour.
Nutritional factors that can underpin changed behaviour in horses include:
- Overfed, underworked
- High starch or sugar intake
- Gut-related pain
- Mycotoxin ingestion
- Microbiome and the Gut-Brain axis
- Dietary deficiencies and mineral imbalance.
Overfeeding of hard feeds is one of the most common causes of hyperactive behaviour in horses. When horses consume more calories than they use in a day, they will store some excess energy as body fat, and often use some of it for ‘play.’ The key to avoiding exuberant misbehaviour is to match calories consumed with calories burned.
The amount of hard feed a horse needs each day will depend on the sugar and starch (calorie) content of the forage and the horse’s requirement for body maintenance, growth and workload. Changes in pasture or hay quality and intake aren’t always easy to observe, so it is important to regularly monitor horse body condition for signs that they are gaining or losing weight. Then increase or decrease the size of the hard feed in response to changes in workload and body condition score. Extra calories will be needed for weight gain, and calorie reduction for weight loss as required.
High sugar or starch intake
Although many working horses perform very well on grain-based hard feeds, some horses are prone to displaying ‘hot’ behaviour and become easily excited or nervous on high sugar or high starch diets. The reasons for this are largely unknown but are likely due to spiking blood sugar levels and/or gut issues related to the microbiome via the gut-brain axis (see below), or pain caused by gastric ulcers or hind gut acidosis.
Scientists have evidence that the balance of gut microbes within mammals has a direct impact on the endocrine system responsible for regulating the messaging hormones that send signals from the gut to the nervous system and brain.
The pain caused by gastric ulcers in both the squamous (upper) and glandular (lower) regions of the stomach is frequently a cause of poor or changed behaviour. Gastroscopy is required for a correct diagnosis, and the treatment protocol will be different depending on ulcer severity and the affected region of the stomach. Lifestyle and dietary changes are usually necessary for successful management of gastric ulcers.
Horses prone to ulcers need free choice access to forage (unless overweight) and should avoid cereal hay or chaff as well as cereal grains and by-products including barley, wheat, oats, corn, millrun, bran and pollard. Also avoid feeds with added molasses or honey – read the labelling on the bag carefully. Choose low GI hard feeds by mixing your own or looking for premixed feeds made from legume grains (e.g. lupins), ‘super fibres’ (like beet pulp or soy or lupin hulls), oilseed meals or oil. Feeding lucerne just prior to exercise is also recommended to buffer stomach acid and prevent splash burning the squamous region of the stomach.
Hindgut acidosis occurs when high levels of undigested starch and sugar overflow into the caecum and colon. Microbial fermentation of sugar and starch in the hindgut produces a different balance of volatile fatty acids (VFAs) than those produced by fibre fermentation and this leads to a drop in hindgut pH which can cause ulcers in the gut lining.
Hindgut acidosis can occur suddenly such as when horses are turned out onto a fresh paddock of lush, high sugar pasture, or after the quick introduction of high starch hard feeds. The acidic hindgut environment kills the fibre-fermenting gut microbes and when the change occurs suddenly, high levels of endotoxins released from the dead organisms pose a severe colic and laminitis risk. Chronic hindgut acidosis occurs from starch overload as occurs when horses are fed large meals of high starch ingredients because undigested starch moves beyond the point of absorption in the small intestine.
Minimise the risk of hind gut acidosis by limiting meal size of high starch ingredients to no more than 500 grams per 100 kg of horse bodyweight every 6 hours and limiting access to high sugar grass (especially lush new shoots in autumn and spring, or following a frost). Research shows that the addition of protected forms of the live yeast Saccharomyces cerevisiae stabilizes hindgut pH by favouring microbes that produce a less acidic VFA profile. Buffers such as protected bicarbonates that are able to reach the hindgut can also be a useful tool in minimizing the risk of hindgut acidosis when starch and sugar intakes cannot be reduced sufficiently.
Mycotoxins are harmful substances produced by bacteria and fungi that grow on forage and grains. They can be present in pastures and grains pre- and post- harvest as well as in hays and silage. They may build up if unprocessed grains or manufactured feeds are not well stored and cannot be detected by smell, taste or the naked eye.
After ingestion, mycotoxins can negatively impact gastrointestinal function, disrupting the intestinal mucosa and the microflora of the digestive tract before being absorbed into the bloodstream. Mycotoxins can cause permanent damage to the brain, nervous system and organs.
The symptoms of mycotoxin load in horses can be very broad depending on many factors including the type and amount of toxin present and the individual’s immunity or tolerance to mycotoxins. It is not unusual for one horse in a paddock to be much more affected than others on identical feeds. Symptoms of mycotoxin issues affecting the nervous system may include:
- Unpredictable, irritable or spooky behaviour, which is out of character for the horse’s temperament;
- General crabbiness when ridden, pinning ears, swishing tail, kicking out;
- Girthiness, not standing for saddling/mounting;
- Tight, tense, impulsive flight response;
- Head shyness and sensitivity to touch, noise or sudden movement;
- Aggressiveness towards people or horses;
- Hormonal behaviour in mares and ‘riggy’ behaviour in geldings;
- Abnormal separation anxiety; and
- Head shaking or flicking.
Adding a broad-spectrum mycotoxin binder to the feed can help to address these issues. Options to reduce exposure to mycotoxins can include limiting grazing hours or removing horses from affected pastures during certain times of the year.
Microbiome and the Gut-Brain Axis
Exciting new research is emerging to demonstrate the significant influence of the gut microbial population on animal health and behavior. Disruption of the balance of gut microbial species (as occurs during stress) has been demonstrated to cause behavioral change in some species.
Animals treated with probiotics have measurably lower levels of corticosterone, a stress hormone. Scientists believe that supplementation with probiotics to improve digestive comfort is a plausible strategy that could contribute to behavior modification in horses. Supplementation with live yeast Saccharomyces cerevisiae or specific Lactobacillus bacterial species maintains the natural diversity of hindgut bacterial populations. This reduces the levels of lactic acid and maintains a more stable hindgut pH which could reduce the impact of stress on the gut and avoid potentially behaviour-modifying deficiencies in the vitamins and amino acids normally provided by a healthy hindgut microbiome.
Dietary deficiencies and mineral imbalance
When a horse’s body lacks the essential nutrients to maintain the nervous system in good order, various behavioural and neurological symptoms commonly referred to as ‘grass-affected behaviour’ can occur. For example, grass tetany and staggers can be causes by an imbalance in the macrominerals sodium, magnesium, nitrogen and potassium.
Dr Thomas Swerczek, a veterinary pathologist at the University of Kentucky says that grass has a dramatic effect on electrolyte balances and metabolism in horses, and when grass is stressed, dramatic changes occur. Supplement changes may be necessary to deal with stressed pasture forages, especially grass in the spring and autumn when cold-stress and drought stress occurs. The use of herbicides also dramatically stresses grass pastures. The levels of potassium and nitrate spikes in stressed plants, and sodium will decrease in pasture forages. The excessive potassium and nitrate can be corrected by adequate salt in the diet, both as a preventive and when symptoms are acutely occurring.
Calcium and magnesium levels need to be balanced to maintain normal muscle contraction and relaxation so ensuring correct dietary balance between calcium, phosphorous and magnesium is critical to optimize uptake and avoid painfully tight muscles after work. However, no scientific evidence exists to support the use of excessive amounts of magnesium or calcium in any form to improve brain function or reduce excitability. A high oxalate intake from many species of tropical pasture including kikuyu, setaria and buffel grass is a common cause of calcium deficiency. Many diets lack adequate magnesium to achieve an optimal calcium to magnesium ratio, creating a need for magnesium oxide supplementation.
B-group vitamins are important for energy metabolism and nervous system function. Signs of deficiency include decreased appetite and increased irritability. The gut microbial population is responsible for production of much of the vitamin B that horses require so supplemental vitamin B is required in times of stress and by hard working or breeding horses.
Scientists have found that omega-3 fatty acids in the form of DHA and its precursor, EPA, can improve cognitive function in humans. Research from many species demonstrates that DHA is essential for normal brain development before and after birth. New work is linking EPA to mood and behavior. Perhaps in future we will see research linking marine-sourced omega-3 supplementation (DHA and EPA) to improved horse behavior and learning!