Sleep Deprivation by Dr Tom Ahern

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By Dr Tom Ahern



Is your horse crazy…or just tired and irritable?


ur horses seem to have an idyllic life as, apart from the very short time most of us are riding or training them, they spend their days either sleeping or eating. We are accustomed to seeing them either flat out in the paddock or standing with head drooping and catching a nap. But just how much sleep does your horse need and…is it actually getting enough? Sleep is essential for a horse’s well-being, yet it is rarely considered as part of our management plan. It’s not just any sleep that is necessary, the horse must have at least 30 minutes a day of rapid eye movement (REM) sleep, which occurs where it enters a state of temporary unconsciousness and its muscles become inactive and

About the Author: Dr Tom Ahern BVSc MRCVS Equine Veterinarian and Researcher.

Dr Tom Ahern graduated from Sydney University in 1978, then entered equine practice. Very early in his career he became interested in breathing problems in horses and began developing his own surgical approach to deal with some of the more common issues. Since Tom1990’s Ahern - the early he has worked exclusively in this field.

W: www.DrTom P: 0423 246 144 E: February/March 2021 - Page 58

completely relaxed. This only happens when the horse is lying down. Horses that are sleep deprived can exhibit a number of physical and psychological behaviours.

SLEEP PHASES There are four phases of sleep a horse experiences - diffuse drowsiness, intermediary, slow wave and paradoxical or ‘deep’ sleep. The specific type of sleep deprivation that is most concerning is a lack of paradoxical, or ‘deep’ sleep, which normally occurs whilst the horse is lying down (lateral recumbency).

DEEP SLEEP OR PARADOXICAL The fourth phase, referred to as paradoxical or ‘deep sleep’, occurs when the horse lies down (lateral recumbency). In this phase, REM occurs. A horse only requires approximately 30 minutes of this type of sleep daily.

DIFFUSE DROWSINESS This can occur whilst the horse is standing. At this stage, the horse has one hind limb off the ground whilst supported on the other three legs. Its head is slightly lowered and usually to one side.

INTERMEDIARY PHASE The next phase occurs just before the horse sits down (referred to as achieving ‘sternal recumbency’ where the horse is lying down on its stomach, with its legs tucked and head and neck off the ground). Again, on three legs but now the head is lowered to wither level. This is an alert phase where the horse checks its environment to make sure there are no predators about and that a companion animal is on guard to warn them if one does appear.

SLOW WAVE Next the horse moves to the sternal recumbency position. Diffuse drowsiness is resumed and then the third phase of ‘slow wave’ sleep begins.

This fourth phase often occurs in the early morning, a time when most predators are also asleep. During this phase of sleep the body’s muscles (except the respiratory muscles) are so relaxed that they are in a state similar to that of paralysed muscles. The horse therefore could not support its frame in any position other than recumbency. Very occasionally this ‘deep’ or REM sleep occurs whilst the horse is still in a sitting position or sternal recumbency with its head to one side. If REM sleep was to occur whilst standing the horse would collapse due to the sudden muscle relaxation.

SLEEP CRASHING As much as all phases of sleep are important and any degree of sleep deprivation will quite obviously impact both performance and behaviour, as it does with ourselves, it is a lack of paradoxical sleep that impacts a horse’s life most dramatically. A horse can go without this form of sleep for extended periods (up to several weeks), however, continued deprivation can lead to what is referred to as ‘sleep crashing’.

Are they convulsions? Does your horse have a brain tumour? Or is IT just crazy? Your horse goes from being calm and relaxed one minute to highly reactive and even explosive the next. You may be adjusting some tack, beginning a ride, tightening the girth, or walking it out of its stall when it suddenly… • leaps forward • rushes backwards • collapses onto its knees • explodes for no reason

Firstly, a few questions! Does it struggle with body condition? Is its coat unhealthy? Is its behaviour highly unpredictable? Does it yawn occasionally, or more often? Does it rarely lie down, including in the early morning? Does it spend abnormal periods of time lying down, usually in the late morning? Does it usually sleep on its haunches (sitting up) with its head to the side rather than lying down? Is this usually a ‘very relaxed’ but also in some circumstances ‘unpredictable’ horse …in reality just a ‘very tired animal’? As much as there may be a number of explanations for these changes and altered behaviours, the possibility that your horse may be suffering from sleep deprivation should always be considered.

Quite simply, with a continued lack of this deep sleep, the horse’s brain will eventually decide to initiate sleep regardless of the circumstances, often at rather disconcerting times. You may be adjusting a piece of tack or leading your horse out of its stall when it suddenly buckles at the knees and begins to collapse. At the same time, you may notice its eyeballs roll backwards and flicker. Your horse then wakes just as suddenly, often in a semi- panicked state, and then regains its stance. Occasionally they will then leap forwards or backwards. Continued February/March 2021 - Page 59

SLEEP TERRORS ‘Sleep terrors’ are a less common consequence of sleep deprivation. They can be very dramatic though - with sudden explosions of sometimes violent and seemingly uncontrolled behaviour. This can include crashing into walls, galloping whilst kicking out behind as if a dog is snapping at its heels and, during these periods, emitting sounds that have been best described as ‘horse screaming’!

Your horse can wake suddenly, often in a semipanicked state.

‘Sleep crashing’ is often confused with another sleep disorder referred to as ‘narcolepsy’. This condition is quite uncommon in horses. With narcolepsy, the affected horse will not attempt to support itself when it suddenly falls asleep and will crash to the ground and lie there.

The most common reason for a horse becoming sleep deprived would be the lack of a companion or ‘guard’ that they are comfortable with, to keep an eye out for predators or other dangers whilst they are asleep.


‘Hypersomnia’ is another consequence of sleep deprivation, which is defined as a feeling of excessive sleepiness. These individuals are often referred to as being very relaxed but in fact may be too relaxed. They may be seen yawning occasionally or in some cases frequently. They may also spend excessive amounts of time lying down, which often occurs in the late morning.

CASE DESCRIPTION In July 2013, a rising 4-year-old unraced Thoroughbred gelding was purchased to be trained for dressage. In October, the horse was sent to a breaker to be re-schooled as its aberrant behaviour suggested that its original education may have been inadequate. On the ground the horse appeared to have a split personality.

It was extremely lethargic and frequently seen yawning, was prone to tripping and stumbling when walked in-hand and yet could also become aggressive, biting and lashing out when being geared up.

significant or incriminating abnormalities. Despite frequent observations, only one report on the state of its eyes during these prolonged recumbencies was available. On this occasion the eyes appeared to be in a state of rapid eye movement (REM) but remained open. At one point the lids did close momentarily before opening again. Several months later a professional trainer of some thirty years experience was employed to take over the horse’s education as it appeared to have little respect for its owner and others who were involved with its handling.

One other unusual behaviour was its daily routine of moving to lateral recumbency (lying down) for extended periods of up to two hours at a time. This most often occurred around late morning.

One example of what was perceived to be a lack of respect was when, on a number of occasions and with different attendants, as the lead rope was being attached, the horse would suddenly lurch forward and walk straight over the handler. At other times, the horse would firstly roll its eyes into the back of its head as occurs in an oculogyric crisis (OGC). It would then take several short steps forward and launch itself into the air. On landing, it appeared to return to a normal state. This did not occur under saddle. In the months that followed these incidents the handler adopted the tact of using physical and audible stimulation to arouse the horse when altered behaviours were anticipated.

Several veterinary examinations of both a medical and orthopedic nature revealed no

There appeared to be some reduction in these, however the lethargy, stumbling and daily

The lethargy and inattentive stumbling was also apparent when being ridden but at this stage there were no aggressive traits exhibited when under saddle.

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Recumbencies In August 2014, the horse was taken to a training camp and yarded overnight without company. The following day, it was readied for its lesson and mounted. It took two steps and then exploded. A period of uncoordinated bucking and kicking then followed, which lasted for several minutes. This behaviour from a horse previously described by its owners as lethargic and rarely seen exercising. As time passed, the episodes of unpredictable behaviour continued. On several occasions whilst standing in the wash bay, an oculogyric crisis (OGC) would be evident. The horse would then launch itself into the air, halt, charge forward, launch, halt and continue this for up to a minute.

On one occasion when the horse had just been saddled, it suddenly exploded, crashing into walls, seemingly oblivious to the presence of obstacles or people. It then leapt out of the barn and charged over two twenty metre sand piles and eventually careered into a ditch. These were obstacles that in normal circumstances this horse would avoid.

Dominant mares are often the most trusted. Other reasons include stable and show protocols that are constantly interrupting a horse’s sleep, older horses with arthritic joints that may find it difficult to lie down and/or get up, and late pregnancy - with the associated large abdomen that makes lying down both difficult and uncomfortable for a mare. There is also another, less common, cause that has yet to be fully investigated. Some horses appear to suffer from a form of obstructive sleep apnea (OSA), that is well-documented in people. During deep sleep, a horse’s breathing muscles are very relaxed. Their upper airways (throat) collapse more commonly when these respiratory muscles are relaxed or fatigued. This situation in the exercising horse is commonly referred to as ‘choking’ or technically as palatal instability (PI), dynamic pharyngeal collapse (DPC) or dorsal displacement of the soft palate (DDSP). If these conditions occur during the deep sleep phase, then the horse can be suddenly aroused. If this happens frequently it can deter the horse from seeking recumbent sleep and it may then attempt to get its REM sleep whilst sitting, or worse, be forced into this deep sleep phase whilst standing. This new theory has arisen with observations of changed sleep habits following surgery to reduce the impact of these upper airway dysfunctions.

In May 2015, the daily periods of recumbency appeared to cease. There had been no significant changes in environment or herd status as the horse was on the same property and still paddocked next to a dominant mare.

Screaming After this, the next major incident was when the property owner was awakened at 2am by the sounds of what she described as “blood curdling screams” coming from the barn. The horse was found staggering, screaming, lashing out and throwing itself on the walls with such force that plaster was being dislodged in the next room. There appeared to be little coordinated or conscious control over these actions. Several minutes passed and the events ceased. Two further incidents occurred when the head collar was being fitted prior to bringing the horse in from the paddock. On the first occasion, the horse lurched forward knocking the handler to the ground before collapsing. The second episode was more severe. As the head collar was being placed, the horse firstly extended its head and neck and its body appeared to stiffen. Rapid eye movements were evident before it collapsed backwards over the fence. It then

How do you know if your horse is getting enough sleep and, in particular, paradoxical sleep? Obviously, personal observation is first but if that is not practicable, a night vision camera or a rug sensor will give you a good idea of how long your horse spends lying down. If you believe - through observation of a lack of recumbent sleep or the presence of behavioural changes - that your horse may not be getting enough sleep, then you should consult your veterinarian or a qualified animal behaviourist. In most cases, changes in the horse’s routine, environment or companion will result in a return to normal sleep habits. Medication in the form of a tailored pain relief program may be required where joint or arthritic pain is preventing your horse being able to lie down. However, if these changes do not lead to a resumption of normal periods of sleep while lying down then the possibility that your horse is experiencing a form of equine ‘obstructive sleep apnea’ triggered by upper airway collapse should be considered. For this assessment you will need to consult a veterinarian who is experienced in this area.

got to its feet and careered down the fence line, staggering and kicking out as though a dog was snapping at its heels. The previously described screaming then began whilst the horse continued cantering about the paddock. Several minutes later this behaviour ceased and the horse was able to be taken in-hand. It was sweating profusely, tachycardic with visible pulsations of the chest wall.

Treatment On the 29th of August 2015, the horse presented at the author’s practice. At this time, fourteen weeks had elapsed since there had been any evidence of recumbent sleep. There had been no significant environmental or social changes during this period and historically the horse was able to physically attain recumbency An upper airway examination revealed significant ulceration and wear of the mid-free border of the soft palate. In the author’s opinion this was typical of the changes seen in cases of chronic PI [9,11]. In the absence of any other etiological avenues, the possibility that PI [9] or pharyngeal instability [12] with resultant UAO may have been impacting negatively

A group sleep obviously horses that are comfortable in their environment and with their companions. Dr Tom Ahern reported that after his article Roar No More, in the Dec Jan issue, he performed surgery on a horse that the owner described as doing ‘all those things’ mentioned in the article. After working the horse for the first two days (following surgery) the owner declared that its breathing was normal for the first time in its life!

on the horse’s ability to experience sufficient paradoxical sleep was discussed with the owner. It was agreed the horse would undergo an oral palatopharyngoplasty (OPP) [13] procedure in an attempt to reduce the incidence of this instability. Following surgery, the horse was rested for eight weeks prior to resuming training. In the immediate postoperative period the horse, which was already in poor condition, lost considerably more weight.

RESULTS In the eight months since resuming ridden exercise the horse had steadily gained weight. There had been no significant alterations to its diet. It was now described by its owner as being in extremely good condition with a normal healthy coat. The horse also resumed regular recumbency although more often during the evening rather than late morning, which had been its habit. There had been no further episodes of collapsing, screaming or other untoward behaviours. Stumbling was now a rarity and the horse was described as being alert and keen to work. The yawning had ceased. February/March 2021 - Page 61


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