Understanding and treating depression in horses

Introduction

While depression is widely recognised in humans, it is a condition which is often overlooked in animals. The symptoms and clinical signs of depression vary from species to species but recent studies have shown that humans and horses share some characteristic warning signs which are important to recognise.  

Horses are prey animals with a well-developed fight-or-flight response and their behaviours are controlled by the nervous and endocrine system.  Like all animals, behaviour is influenced by many external factors that include genetic predisposition, environment, physiology, experience and learning. Foals are neurologically mature at birth and soon after birth can identify and react to dangerous stimuli, but like humans, the horse’s brain function does decrease with age resulting in increase in anxieties and fears. 

The brain and its neurotransmitters play an instrumental role in the temperament and behaviour of the horse; therefore, abnormal levels of various hormones can lead to a change. Normal survival instincts for the horse fall into two broad categories that includes ‘something to fear and must flee’ and ‘something not to fear and should be explored or ignored’. New research has also demonstrated that there is not a linear dominance hierarchy but rather the herd communicates with positive reinforcement and less from punishment.

In order to achieve the best results when training, it is important to consider these natural behavioural instincts. Maintaining a positive mental attitude in both training and management regimes for the horse will have considerable benefits to performance and reduce negative behaviours. 

What is depression? 

Depressive disorder (also known as depression) is a mental disorder that can occur in horses.  It involves a depressed mood or loss of pleasure or interest in activities for long periods of time.  Depression affects how the horse thinks and behaves and may lead to a variety of potential physical problems.  

While depression is widely recognised in humans, it is an illness which is often overlooked in animals.  The symptoms and clinical signs of depression vary from species to species but recent studies show that humans and horses share some characteristics. With racehorse welfare being a key topic at present, understanding and recognising small behaviour changes can allow for small management adaptations to be made thus enhancing the horses wellbeing. 

The research 

Recent research from France alongside the growing body of research, suggests that horses may develop something similar to depression in a response to physical or social discomfort.   

Researchers have observed horses that become withdrawn because of undergoing a cognitive shift.  It has been found that horses tune out to their surroundings due to physical or psychological stress.  Horses have the cognitive ability to be attentive; however, with the presence of chronic stressors there is a delay in a horse's response as they have “switched off” from their environment and demonstrated sensory inattention. 

Because we do not truly know how the horse is feeling, the hypothesis currently being considered is that the horse develops an “inward-oriented attention” when subjected to chronic disorders.  It must be stressed that this long delay in attentiveness does not indicate a state of calm for the horse but a withdrawal from its surroundings. 

Dr Georgia Mason from The Ontario Veterinary College has suggested that a horse may respond similarly to humans with depression.  It is thought that the horse’s withdrawal can be a result of a ‘learned helplessness’ in that responding to negative stimuli does not make any difference.  Thus depressed people are prone, for example, to judge ambiguous stimuli as being unlikely to be positive and to recall unpleasant memories more readily than pleasant ones.

In addition, a number of studies have assessed cortisol levels in those horses that are withdrawn. Cortisol acts to assist in relieving stress by increasing glucose metabolism to provide energy, which then enables the horse to escape from the stress. In the short-term, cortisol release is beneficial to the horse to help it cope with a stressor. This study found that abnormally low levels of cortisol (hence a physiological depression) were found in withdrawn horses that are in a pathological and depressed state.  These depressed horses also expressed anhedonia, which is the loss of pleasure to feed on an appetent substance.  

Further studies and research are needed to better understand the pathology of depression in horses.  It has been suggested that the life conditions, such as food, space, social conditions and health problems should be questioned and observed in order to identify potential acute or chronic stressors that may lead to depression. 

However, there are reviews that question the current animal models of depression and suggest that ethological models of mood disorders based on animals living under natural conditions need to be improved and developed. 

Symptoms of a depressed horse 

It is important to become acquainted with potential signs of depression in the horse so that you can identify them quickly.  By identifying the symptoms of depression, one can rapidly begin the task of identifying the underlying cause such as an injury, illness, social or environmental stressor.  With these tools, one can reduce the risk of the short-term and long-term negative effects that could ultimately hinder the horse’s health and performance.  

Lack of response

In humans and animals, being attentive is one aspect of subject cognitive abilities and capacities. The delay in responding to stimulation shows that withdrawn horses ‘switch off’ from their environment and show sensory inattention. Such lapses of attention are likely to be associated with the chronic effect of stressors, which might be expected to induce a lowered state of arousal.

A French study from the Universite de Rennes, demonstrated that depressed horses that were subjected to a series of five new, unique and unusual sounds were significantly less likely to pay attention to the noises compared to normal horses.  Their findings demonstrated that the withdrawn horses had undergone a cognitive shift that they were so physically or psychologically stressed that they developed sensory inattention. 

Heightened anxiety 

While the depressed horse will often be disinterested in everyday activities, people and companions, they are likely to demonstrate heightened emotions towards challenging situations and new stimuli as they try to express their discomfort. Stimuli that are usually unremarkable to the horse may become uncomfortable for the horse and make them “spooky”, anxious or fearful when they weren’t before. 

Lack of interest in food 

A change in mental well-being in your horse can lead to a loss of appetite.  The potential complications are the loss of weight, condition, muscle development, fitness, energy levels as well as the increased susceptibility to infection and prone to other health conditions such as colic or gastric ulcers. 

There are other illnesses and ailments that can lead to inappetence; hence, it is worth seeking veterinary advice in order to rule out any other physical problems.  

Anhedonia

Dr Carole Fureix looked at anhedonia which is the loss of feeling pleasure from experiences that used to be pleasurable.  This symptom is prominent in the depression of humans. Her study demonstrated that horses who are at times withdrawn are more anhedonic than those that are not withdrawn.  She concluded that this is a key symptom of clinical depression and suggests that withdrawn horses are indeed in a depression-like state.  

The horse may show unwillingness to work or no longer take pleasure in work they used to enjoy. This is especially important when considering rider and horse safety too as a withdrawn horse may not react appropriately to potentially dangerous situations.

Posture

Standing facing the stall wall for periods of time while demonstrating a withdrawn posture showing a fixed gaze, neck stretched out level with back, eyes open but lack of eye and ear movement. This differs from a content horse that is resting and displaying relaxed muscles, laterally rotated ears, the drooping of its eyelids and lips and holding its neck such that it slopes lower and rounder.  

Physical changes are perhaps somewhat easier to spot with a withdrawn posture being one of the typical signs of depression.  A healthy and content horse will stand with their head up and ears moving inquisitively.

Causes of depression 

The domesticated horse is often managed in such a way that they cannot express their natural behavioural instincts, thus exposing them to stressors which can lead to depression.

Lack of adequate positive social interaction with other horses 

A study from Michael Steger and Todd Kashdan explained that dysfunctional social behaviour has been implicated in the experience of depression. 

In addition, Timothy Elmer and Christoph Stadtfeld described individuals with depressive symptoms are more likely to be isolated from their social group(s), which can further increase their symptoms.  

Similarly, lack of social interaction without conscious choice for extended periods of time can lead to depression in humans.

Lack of adequate exercise and/or turnout 

It is well documented in human medicine that exercise and physical activity can improve many health conditions. Research on depression, anxiety and exercise demonstrates that the mental health and physical benefits can help improve mood and lessen anxiety.  The link between depression, anxiety and exercise are not entirely clear.  It has also been shown that exercise and physical activity may help keep depression and anxiety from coming back. 

Companionship reduces stress in the horse, hence naturally  living in a herd.  Horses are able to form companionships with their own species and other animals including humans.  In fact, horses kept in isolation, such as in closed stables, can become anxious, flighty and difficult to manage. 

Exercise releases endorphins which are feel-good chemicals in the body and also allows for more social interaction.  A recent University of London study demonstrated that people with low aerobic and muscular fitness are nearly twice as likely to experience depression.  

Illness or injury that causes pain or discomfort 

In humans studies have found that anywhere between 30-85% of patients suffering from chronic pain are also clinically depressed. Other illnesses in humans such as nutritional deficiencies, cushing’s disease, lyme disease, chronic pain, and insulin resistance can cause depression.

Stress during training, competing or in the daily routine 

If there is chronic stress in which the horse’s physiological stress response is taxed beyond what it is designed to do it can begin to impair the horse possibly leading to depression 

Inflammation and depression 

There is evidence that there is a link between inflammation and depression. Inflammations that lead to serious depression in humans can be caused by infections such as those caused by bacteria, viruses or even parasites.  There is increasing evidence that inflammation can cause depression because of the increase of cytokines setting the horse’s brain into “sick mode”.   

Treating depression

Simple changes in management can help treat the underlying cause of depression and can substantially improve the horses well-being thus having a positive impact on performance.

Light therapy

Modern management methods mean that horses can spend a large amount of time stabled which impacts the horse’s circadian rhythm (body clock). 

A study was performed at Nottingham Trent University where trial horses were put under an hour of high intensity broad spectrum light every day for six weeks. Their behaviours regarding feeding, sleep patterns and attitude to being handled and ridden were compared to a group of horses that had not received the therapy. The untreated horses were noted to be sleeping longer, lazier at ridden exercise and grumpier.

Light therapies have many positive benefits that can reduce signs of depression and improve overall well being; better daytime alertness and improved rest and sleep pattern, extending summer coat and body condition and encouraging the body to convert feed to muscle mass, noticeably fewer stable vices such as box walking, cribbing, weaving and reduced bacterial pathogens and fungal load leading to improved respiratory function.

Management

Racing is already making moves to ensure the best welfare conditions for horses, with German trainers now having to comply with regulations regarding size of stable, the amount of light in the stable, the provision of windows enabling horses to socialise and turn out capacity for a minimum two hours per day.

Increasing turnout time is reported to have positive effects on their horses' mental wellbeing, reduces stiffness and lowers the rate of stable vices. It also allows the horse to make social connections whilst allowing them to show their natural instinctual behaviours. 

With horses in varying routines in large yards, this can sometimes become stressful to some individuals. By providing company of other horses when stabled, this can help with social interactions and reduce stress. Stable enrichment and adlib forage can also replicate positive behaviours in the stable. 

It is known that exercise releases ‘feel good’ endorphins, thus, keeping the horse in a regular training regime complimented with the correct nutrition will be beneficial. 

Veterinary advice

It is important to seek veterinary advice should the horse be exhibiting signs of depression to help identify the underlying cause. Diagnostics such as blood tests can ensure there is no infection present and work-ups will highlight any pain or discomfort.

Conclusion 

While depression is widely recognised in humans, it is an illness which is often overlooked in animals. Depression in horses can be significant and harmful regardless of the underlying cause and can be temporary or long term. It is vital to ascertain the underlying cause of depression in a horse in order to treat and remedy the illness. 

Starch v fibre intake. Balancing different carbohydrate sources against changing requirements of fitness, injury and recovery

Starch or FibreBalancing different carbohydrate sources against changing requirements of fitness, injury and recoveryCarbohydrates are by far the largest component of any horse’s diet, typically two thirds by weight, yet we often focus more on other…

By Catherine Rudenko

Carbohydrates are by far the largest component of any horse’s diet, typically two thirds by weight, yet we often focus more on other nutrients, such as protein—which in comparison forms only a small portion of the total diet at around 8-13%. Carbohydrates, specifically the balance between differing carbohydrate sources, influences three key areas relating to performance.

The choice of carbohydrate influences the type of energy available, providing varying proportions of ‘fast release’ or ‘slow release’ energy. The type of carbohydrate chosen also impacts behaviour, increasing or decreasing risk of excitability and certain stereotypical behaviours. Last, but by no means least, the choice of carbohydrate and the way in which it is fed impacts digestive health and the ability of the digestive system to convert food to ‘fuel’ for the body.

Getting the balance right between the different types of carbohydrates is important for getting the right results when having to adjust the intensity of training, when resting a horse and when working back up through the stages of fitness. 

What are carbohydrates? 

There are different ways of classifying or grouping carbohydrates, depending on whether you take things from the plant’s point of view or that of the digestive anatomy of the horse. Working with the horse in mind, carbohydrates are best classified by the section of the digestive system that they are processed in—either the small intestine or large intestine. The site of digestion determines the type of energy provided, often referred to as fast releasing for the small intestine and ‘slow releasing’ for the large intestine. The group of carbohydrates, known as hydrolysable carbohydrates, are the group behind the description of fast releasing, whilst the group known as fermentable carbohydrates are those forming the ‘slow releasing’ category. Within the fermentable group, there are three sub groups of rapid, medium and slow. 

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What are carbohydrates made of? 

There are many types of carbohydrates in the horse’s diet, ranging from simple sugars to more complex structures. They are defined by their degree of polymerisation, which refers to the way in which sugar units are joined together. How a carbohydrate is formed and the type of link present are important as they determine if digestion is possible in the small intestine or whether fermentation in the large intestine is required. This influences the type of energy available. 

For horses in training, the type of carbohydrate of particular interest is the polysaccharide group which includes starch, cellulose, hemicellulose and fructans amongst others. Starch is found in significant quantities in hard feeds, whilst cellulose and hemicellulose, amongst other fermentable carbohydrates are abundant in forages. Pasture is a source of fructans, which can change rapidly depending on growing conditions and daylight hours. 

Structure

Single sugars, also called simple sugars, comprise one unit only. They are categorised as monosaccharides—the most commonly known being glucose. For horses in training this is a highly valuable sugar as it is the main ‘fuel’ for muscles. Glucose forms the basis of many of the more complex structures of interest to horses in training.

When two sugars join together, they are known as a disaccharide—the best known being lactose which is found in mare’s milk. Oligosaccharides refer to more complex structures where more units are joined together—a common example being fructo-oligosaccharide (FOS) which many horses in training are specifically fed as a prebiotic to support digestive function. 

Type of Carbohydrate

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Polysaccharides, our group of particular interest, are significantly more complex chains that are branched and are not so easily digested as the simple sugars. The branched nature of polysaccharides, such as starch and cellulose, are the result of links between chains of sugars. The type of link present determines whether or not it will be possible for the horse to digest this form of carbohydrate in the small intestine or not.

Starch

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Starch is the primary carbohydrate of interest in our hard feeds. It is a hydrolysable carbohydrate, which can be digested in the small intestine, releasing glucose into the bloodstream. For horses in training this is the most important fast release energy source. Starch is found in all plants, with the highest quantities seen in cereals such as oats, barley and maize.

Composition of cereals commonly used in racing feeds

Starch is made up of two types of sugar chains: amylose and amylopectin, which are formed from glucose units. Amylose itself is easily digested, however amylopectin has a different type of bond connecting each branch, which the enzymes of the small intestine cannot break down. Feed processing, which changes the structure of starch and breaks apart the previously indigestible bonds, is therefore a key factor in ensuring that when starch is fed that the maximum amount of glucose is derived. 

Amylose and Amylopectin 

Feed processing comes in many forms, from simply crushing or rolling the grain to cooking techniques including micronizing, steam flaking, pelleting or extruding. The amount of processing required for what is deemed efficient digestion differs by grain type. Oats have a natural advantage within the cereal group as they can be fed whole, although processing can still improve digestion. Barley, wheat and maize cannot be fed whole or simply rolled. They require cooking to ensure that starch becomes available, and the impact of cooking processes is much greater for these grains. 

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The availability of starch is assessed through the amount of glucose released into the blood after feeding. The study below shows the effect of steam cooking maize (corn) compared to two processes that simply change the physical appearance, cracking or grinding. Steam-flaked maize is more available as shown by the greater glucose response. 

Starch is a fast release energy source, being digested in the small intestine, and the term can easily be misunderstood. It does not mean that the horse will suddenly run at top speed nor appear to be fuelled by ‘rocket fuel’. The word ‘fast’ relates to the relatively short time it takes for digestion to occur and glucose to be available. …

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