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. 

Stem Cell Therapy - the improved diagnostics available to treat lameness

Article by Jackie Zions (interviewing Dr. Koenig)

Prevention is the ideal when it comes to lameness, but practically everyone who has owned horses has dealt with a lay-up due to an unforeseen injury at some point. The following article will provide tools to sharpen your eye for detecting lameness, review prevention tips and discuss the importance of early intervention. It will also begin with a glimpse into current research endeavouring to heal tendon injuries faster, which has obvious horse welfare benefits and supports horse owners eager to return to their training programs. Dr. Judith Koenig of Ontario Veterinary College (OVC) spends half of her time as a surgeon and teacher with a strong interest in equine sports medicine and rehabilitation, and the other half as a researcher at the OVC.

Lameness is a huge focus for Koenig, whose main interest is in tissue healing. “I think over the past 20 or 30 years we have become very, very good at diagnosing the cause of lameness,” says Koenig. “In the past, we had only radiographs and ultrasound as a diagnostic tool, but by now most referral centres also have MRI available; and that allows us to diagnose joint disease or tendon disease even more. We are much better now [at] finding causes that previously may have been missed with ultrasound.” 
Improvements in diagnostics have resulted in increased ability to target treatment plans. With all the different biologics on the market today, Koenig sees a shift in the management of joint disease with more people getting away from steroids as a treatment.

The following list is excerpted from Equine Guelph’s short course on lameness offered on TheHorsePortal.ca. It outlines the different diagnostics available:

When asked for the latest news on research she has been involved in, Koenig proclaims, “I'm most excited about the fact that horses are responding well to stem cell treatment—better than I have seen any response to any other drug we have tried so far!”

Koenig has investigated the use of many different modalities to see if they accelerate tissue healing and has studied which cellular pathways are affected. Two recent collaborative studies have produced very exciting findings, revealing future promise for treating equine osteoarthritis with stem cell therapy.  

In a safety study, Koenig and her team at the Ontario Veterinary College have shown equine pooled cryopreserved umbilical cord blood, (eCB) MSC, to be safe and effective in treatment of osteoarthritis.  

“These cells are the ones harvested from umbilical cord blood at the time of foaling and then that blood is taken to the lab and the stem cells are isolated out of it,” explains Koenig. The stem cells are then put through a variety of tests to make sure they are free of infectious diseases. Once given a clean bill of health, they are expanded and frozen. 
The stem cells harvested from multiple donors of equine umbilical cord blood [eCB, (kindly provided by eQcell), MSC] were compared to saline injections in research horses. “This type of cells is much more practical if you have a cell bank,” says Koenig. “You can treat more horses with it, and it’s off the shelf.” There were no systemic reactions in the safety study. Research has also shown no different reactions from sourcing from one donor or multiple donors.  

In the second study, 10 million stem cells per vial were frozen for use in healing OA from fetlock chips in horses that were previously conditioned to be fit. After the fetlock chip was created, exercise commenced for six more weeks, and then osteoarthritis was evaluated by MRI for a baseline. Half the horses were treated with the pooled MSC stem cells, and the control group received saline before another month of exercise. Then MRI and lameness exams were repeated, and arthroscopy was repeated to score the cartilage and remove the chip.

Lameness was decreased and cartilage scores were improved in the group that received stem cell therapy at the time of the second look with arthroscopy.

Many diagnostics were utilised during this study. MRIs, X-rays, ultrasounds and weekly lameness evaluations all revealed signs of osteoarthritis in fetlock joints improved in the group treated with (eCB) MSCs. After six weeks of treatment, the arthroscopic score was significantly lower (better cartilage) in the MSC group compared to the control group. 

“Using the MRI, we can also see a difference that the horses treated with stem cells had less progression of osteoarthritis, which I think is awesome,” says Koenig. “They were less lame when exercised after the stem cell therapy than the horses that received saline.”

This research group also just completed a clinical trial in client-owned horses diagnosed with fetlock injuries with mild to moderate osteoarthritis changes. The horses were given either 10 million or 20 million stem cells and rechecked three weeks and six weeks after the treatment. Upon re-evaluation, the grade of lameness improved in all the horses by at least one. Only two horses presented a mild transient reaction, which dissipated after 48 hours without any need for antibiotics. The horse’s joints looked normal, with any filling in the joint reduced.
There was no difference in the 18 horses, with nine given 10 million stem cells and the other nine 20 million stem cells; so in the next clinical trial, 10 million stem cells will be used.

The research team is very happy with the results of this first-of-its-kind trial, proving that umbilical cord blood stem cells stopped the progression of osteoarthritis and that the cartilage looked better in the horses that received treatment. The future of stem cell therapy is quite promising!
Rehabilitation
Research has shown adhering to a veterinary-prescribed rehabilitation protocol results in a far better outcome than paddock turn out alone. It is beneficial for tendon healing to have a certain amount of controlled stimulation. “These horses have a much better outcome than the horses that are treated with just being turned out in a paddock for half a year,” emphasises Koenig. “They do much better if they follow an exercise program. Of course, it is important not to overdo it.”

For example, Koenig cautions against skipping hand-walking if it has been advised.  It can be so integral to stimulating healing, as proven in recent clinical trials. “The people that followed the rehab instructions together with the stem cell treatment in our last study—those horses all returned to racing,” said Koenig.  

“It is super important to follow the rehab instructions when it comes to how long to rest and not to start back too early.”

Another concern when rehabilitating an injured horse would be administering any home remedies that you haven't discussed with your veterinarian. Examples included blistering an area that is actively healing or applying  shockwave to mask pain and then commence exercise.

Prevention and Training Tips
While stating there are many methods and opinions when it comes to training horses, Koenig offered a few common subjects backed by research. The first being the importance of daily turnout for young developing horses.  

Turnout and exercise
Many studies have looked at the quality of cartilage in young horses with ample access to turn out versus those without. It has been determined that young horses that lack exercise and are kept in a stall have very poor quality cartilage.
Horses that are started early with light exercise (like trotting short distances and a bit of hill work) and that have access to daily paddock turnout, had much better quality of cartilage. Koenig cited research from Dr. Pieter Brama and similar research groups.

Another study shows that muscle and tendon development depend greatly on low grade exercise in young horses.  Evaluations at 18 months of age found that the group that had paddock turnout and a little bit of exercise such as running up and down hills had better quality cartilage, tendon and muscle.  

Koenig provides a human comparison, with the example of people that recover quicker from injury when they have been active as teenagers and undergone some beneficial conditioning. The inference can be made that horses developing cardiovascular fitness at a young age stand to benefit their whole lives from the early muscle development.

Koenig says it takes six weeks to regain muscle strength after injury, but anywhere from four to six months for bone to develop strength. It needs to be repeatedly loaded, but one should not do anything too crazy! Gradual introduction of exercise is the rule of thumb.

Rest and Recovery
“Ideally they have two rest days a week, but one rest day a week as a minimum,” says Koenig. “I cannot stress enough the importance of periods of rest after strenuous work, and if you notice any type of filling in the joints after workout, you should definitely rest the horse for a couple of days and apply ice to any structures that are filled or tendons or muscles that are hard.” 

Not purporting to be a trainer, Koenig does state that two speed workouts a week would be a maximum to allow for proper recovery. You will also want to make sure they have enough access to salt/electrolytes and water after training.

During a post-Covid interview, Koenig imparted important advice for bringing horses back into work methodically when they have experienced significant time off.
“You need to allow at least a six-week training period for the athletes to be slowly brought back and build up muscle mass and cardiovascular fitness,” says Koenig.  “Both stamina and muscle mass need to be retrained.”

Watch video: “Lameness research - What precautions do you take to start training after time off?” https://www.youtube.com/watch?v=zNHba_nXi2k

The importance was stressed to check the horse’s legs for heat and swelling before and after every ride and to always pick out the feet. A good period of walking is required in the warmup and cool down; and riders need to pay attention to soundness in the walk before commencing their work out.

Footing and Cross Training
With a European background, Koenig is no stranger to the varying track surfaces used in their training programs. Statistics suggest fewer injuries with horses that are running on turf. 

Working on hard track surfaces has been known to increase the chance of injury, but delving into footing is beyond the scope of this article.

“Cross training is very important,” says Koenig. “It is critical for the mental and proper musculoskeletal development of the athlete to have for every three training days a day off, or even better provide cross-training like trail riding on these days." 

Cross-training can mitigate overtraining, giving the body and mind a mental break from intense training. It can increase motivation and also musculoskeletal strength. Varied loading from training on different terrain at different gaits means bone and muscle will be loaded differently, therefore reducing repetitive strain that can cause lameness.



Hoof care
Whether it is a horse coming back from injury, or a young horse beginning training, a proficient farrier is indispensable to ensure proper balance when trimming the feet. In fact, balancing the hoof right from the start is paramount because if they have some conformational abnormalities, like abnormal angles, they tend to load one side of their joint or bone more than the other. This predisposes them to potentially losing bone elasticity on the side they load more because the bone will lay down more calcium on that side, trying to make it stronger; but it actually makes the bone plate under the cartilage brittle.  

Koenig could not overstate the importance of excellent hoof care when it comes to joint health and advises strongly to invest in a good blacksmith. Many conformational issues can be averted by having a skilled farrier right from the time they are foals. Of course, it would be remiss not to mention that prevention truly begins with nutrition. “It starts with how the broodmare is fed to prevent development of orthopaedic disease,” says Koenig. Consulting with an equine nutritionist certainly plays a role in healthy bone development and keeping horses sound.