Equine Headshaking Syndrome

January will be the beginning of my 4th research module at the University of Edinburgh. This entire adventure into academia has been, and continues to be, eye opening and thought provoking as evidence based research confirms ideal practices in Equine Management. 

My first module was on Equine Welfare and Behavior.  Meeting up with others around the world and discussing the plight of horses in today's modern world was a humbling experience. Delving into the natural and ethological behaviors of equids left me amazed that this creature actually survives the constraints we, as humans, sometimes put on them. I highly recommend this coursework, or similar studies, to any and all horse enthusiasts. 

My first evaluated assessment was to compose a summary of current Equine Headshaking Syndrome research. I have shared this research with others that have horses experiencing similar symptoms, especially during the spring and summer seasons, with positive feedback. Always discuss any peculiar symptoms with your equine veterinarian. At any rate my hopes are, that after reading this synopsis, you will be more informed about this puzzling malady.

Enjoy,

Nancy

Causal Factors and Management of Equine Headshaking Syndrome.

Nancy McLean

University of Edinburgh

All horses at one time or another can be observed shaking their head. Usually this normal occasional behavior occurs after a roll in the dirt or when being pestered by flying insects. However, when the horse exhibits a forceful repetitive pattern of flipping the head or nose, and this behavior is accompanied by other symptoms like snorting, sneezing, rubbing the head, and eye or nasal discharge, then it may be considered Equine Headshaking Syndrome (HSK)(Madigan and Bell 2001).   “A syndrome is defined as a group of signs and symptoms that occur together and characterize a particular abnormality or condition” (M. Webster).  Contrast this with headshaking behavior that only occurs while a horse is being ridden. Without other symptoms present, this scenario could be interpreted as a response to pain or pressure from equipment, training technique or avoidance behavior from past experiences.  

True HSK syndrome can be violent. Symptoms are observed at rest and while being ridden and it is classified as a locomotor stereotypical behavior.  More importantly, it is known to have a physical, not an attitudinal, cause. Most horses, with this syndrome, flick the head vertically, but a small number have been found to perform a horizontal and/or rotary motion, as well (Newton and others 2000; Mills and others 2002). It can be very difficult and dangerous to ride horses that are exhibiting this abnormal behavior.  The motion can be so extreme that it can knock the horse and rider off balance.  Leading or long -lining the horse can also be dangerous; due to the flinging head and the distress and anxiety some horses display.  It has been reported that the condition worsens as the nostrils flare with increased vasodilation during exercise (Lane and Mair 1987; Mair and Lane 1990; Madigan and others 1995).

Headshaking Syndrome is not a modern diagnosis it has been documented and discussed in equine veterinary journals for over 100 years (Williams 1899).   It can be highly frustrating for horse owners and veterinarians to treat, as physical causes can be suspected in most cases, but elude a definitive diagnoses (Madigan and others 1995).  Finding a corrective treatment, to alleviate the behavior completely, has proven to be difficult (Lane and Mair 1987). Headshaking Syndrome has been recognized in all breeds, at all ages, in all sexes with predominance occurring in geldings. It seems to be mostly seasonal in nature and has been linked to multiple physical causes that all seem to center around the trigeminal nerve and it’s tributaries (Madigan and Bell 2001; Pickles and others 2011; Roberts and others 2012).  It has been reported that humans experiencing trigeminal neuropathy describe tingling, burning, itching and stinging sensations (Pickles and others 2011; Nurmikko and Eldridge 2001).  Perhaps this can explain the headshaking behavior of some afflicted horses. Although, as with other species displaying possible trigeminal nerve sensitivity, a post mortem look at the trigeminal nerve, brain and head of horses with this syndrome, have yet to reveal any atypical pathology (Newton 2001). 

Another analogy, to a human condition, that helps describe HSK to others is Photic Sneeze Reflex. This is a photic sensitization of the sensory nerves originating from the trigeminal nerve pathway along the optic nerve (Madigan and others 1995, Mills and others 2002, Pickles 2014).  This may explain the propensity of the headshaking symptoms to appear in the spring and continue until autumn. Photic light sensitivity seems to play a role, in these seasonal cases, where most horses show marked improvement at night, on cloudy/rainy days and inside a stall/shelter (Mills and others 2002).

Research has also hypothesized that a possible cause of increased headshaking during bright sunshine may be the increase in the level of atmospheric ozone. “Sunshine induces the formation of ozone from oxygen in the presence of nitrogen dioxide derived from volatile organic compounds in petrol fumes and exhausts” (Brostoff and Gamlin 1998). With this in mind regional differences in demographics may be a consideration. Population density, vegetation and crop production might be a factor (Mills and others 2002). This may explain why some horses are non-headshakers until moved to a new location where they become headshakers, at the dismay of their owners  (Lane and Mair 1987).

 To add to the mix of causes, there is current on-going research, reviewing a hormonal effect, specifically high levels of gonadotropin producing hormones, that could theoretically create trigeminal ganglion instability, which could result in nerve sensitivity or neuropathy (Pickles and others 2011).  This line of research may help to understand the seasonality and sex ratios of the syndrome, but to date has not produced any conclusive results.  

Other causative factors of Equine Headshaking Syndrome that warrant mentioning are allergic rhinitis, ear mites, otitis interna (inner ear inflammation), cranial nerve dysfunction, cervical injury, ocular disease, guttural pouch mycosis, dental periapical osteitis (possible jawbone lesion), and vasomotor rhinitis (Lane and Mair 1987).

Unfortunately, conventional analgesics, anti-inflammatories, and antihistamines, normally administered to horses, do not reduce headshaking symptoms (Pickles and others 2011). 

In light of all these causative factors, HSK is still considered idiopathic, since conclusive diagnosis has proven to be elusive and therapeutic options somewhat limited (Pickles and others 2014).  Current treatment is geared more toward managing HSK than curing it. Treatment options showing some success include the use of nose nets and/or fly mask, Cyproheptadine, Carbamazepine, and Magnesium supplementation.  There are many other proposed therapies, but additional research and trials are continuing in this area (Pickles and others 2014). Below are brief descriptions of the most current and somewhat successful therapies along with known side effects.

The use of equine nose nets and/or facial masks seem to have the best results in treating HSK.  An estimated 75% of owners report some improvement in HSK behavior by using a full or half net (Mills and Taylor 2003). The nose nets appear to control the “bee up the nose” behavior although how they work is unknown. It is theorized that by adding a different stimulus, the sensory input, in the muzzle area, is altered (Pickles and others 2014).

It has also been found that more than 50% of horses with Photic HSK benefit from wearing ultraviolet blocking fly mask than tinted contact lenses (K. Pickles et al., unpublished observations) (Madigan and others 1995).  Side effects of these nets and masks can be panic, and irritation from the material. An acclimation period is recommended along with proper care and cleaning of the nets and masks.

Cyproheptadine is often used to treat human vascular headaches.  There is currently no data on the bioavailability or the interactions of this drug in horses. Two studies in the UK showed no improvement in HSK horses after administering Cyproheptadine. However in the USA, Madigan and Bell (2001) reported that 70% of 61 horses improved moderately to greatly within one week of starting this drug therapy (0.3mg/kg PO (per orally) twice daily). Once the drug was stopped, symptoms returned within several days (Madigan and Bell 2001). Side effects are drowsiness, lethargy, anorexia, and colicky behavior (Headshaking Syndrome Center; Pickles and others 2014).

Carbamazepine is an anticonvulsant drug.  A dose of 2-8mg/kg PO 2 to 4 times daily was successful in 2/9 horses (K. Pickles et al., unpublished observations), but Newton and others did a study that found it to be effective in 88% of the 12 horses in the trial (Newton and others 2000).  In the same study Newton and others found when Carbamazepine was combined with Cyproheptadine, at the aforementioned doses, this combination was effective 80%-100% of the time. Improvement was observed in 3 to 4 days (Pickles and others 2014).  “There is a wide variation in the interactions of this drug between individual horses. This may account for the failure rate in some horses while having success in others. Side effects are dullness, lethargy and drowsiness. (Pickles and others 2014)

Magnesium Supplements have been found to lessen the activation threshold of the trigeminal nerve in HSK horses. Absorption rates and optimal serum concentrations need more research.  Approximately 40% of 58 owners reported improvement in HSK after beginning oral supplementation. Plasma ionized magnesium levels should be measured before beginning supplements and again two weeks later to avoid toxicity, which is reported to be rare.  Doses vary according to the type of magnesium being supplemented. Currently there are many types of oral Magnesium supplements available for horses.  There are no reported side effects. (Pickles and others 2014)

In conclusion, Idiopathic Equine Headshaking continues to be a puzzling syndrome to the equine community of owners, trainers, veterinarians and researchers. Trigeminal nerve involvement seems to have propelled research into a new direction. The complexity of nerve connectors and interactions with sensory stimuli continues to make the cause and effects of HSK a guessing game. Treatments are trial and error on an individual basis.  The goal for all involved should be to continue the quest for answers, through research and education, while always putting the welfare of the horse as our initial priority and purpose.

 References

1. BROSTOFF, J. & GAMLIN, L. (1998) The Complete Guide to Hayfever. 3rd edn. London, Parragon, pp. 153-244

2.  Lane J. G. & Mair T. S. (1987) Observations on headshaking in the horse. Equine Veterinary Journal 19, pp. 331–336

3. Madigan J. E., Kortz G., Murphy C. & Rodger L. (1995) Photic headshaking in the horse: 7 cases. Equine Veterinary Journal 27, pp. 306–311

4. Madigan J. E. & Bell S. A. (2001) Owner survey of headshaking in horses. Journal of the American Veterinary Medical Association 219, pp. 334–337

5. MAIR, T. S. & LANE, J. G. (1990) Headshaking in horses. In Practice 9, pp. 183-186

 6. Mills D. S., Cook S.,Taylor K., & Jones B. (2002) Analysis of the variations in clinical signs shown by 254 cases of equine headshaking. Veterinary Record 150, pp. 236–240

7. Mills D. S. & Taylor K. (2003) Field study of the efficacy of three types of nose net for the treatment of headshaking in horses. Veterinary Record 152, pp. 41–44

8. Neff, P., Headshaking Syndrome Center’s website (2016). Treatments [Online]. Accessed on 15/2/1016.  Available from: www.headshakingsyndrome.com

9.  Newton S. A. (2001) The functional anatomy of the trigeminal nerve of the horse. PhD thesis. University of Liverpool, UK

10. Newton S. A., Knottenbelt D. C. & Eldridge P. R. (2000) Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases. Equine Veterinary Journal 32, pp. 208–216

11. Nurmikko T. J. & Eldridge P. R. (2001) Trigeminal neuralgia – pathophysiology, diagnosis and current treatment. British Journal of Anaesthesia 87, pp. 117–132

 12. Pickles K. J., Berger J., Davies R., Roser J.& Madigan J. E. (2011) Use of a gonadotrophin-releasing hormone vaccine in headshaking horses. Veterinary Recorddoi: 10.1136/vr.c5992

13. Pickles K., Madigan J., Aleman M., (2014) Idiopathic headshaking: Is it still idiopathic? The Veterinary Journal 201 pp. 21-30

14.  Roberts V. L. H., Perkins J. D., Skårlina E., Gorvy D. A., Tremaine W. H., Williams A., McKane, S. A., White, I. and Knottenbelt D. C. (2013), Caudal anaesthesia of the infraorbital nerve for diagnosis of idiopathic headshaking and caudal compression of the infraorbital nerve for its treatment, in 58 horses. Equine Veterinary Journal, 45: pp. 107–110.

15. Williams L. W. (1899) Involuntary shaking of the head and its treatment by trifacial neurectomy. American Veterinary Review 23, pp. 321–326

  

Seasonal information...updated research included!

Great read...for this time of year.

http://www.amazon.com/dp/B00PYSTEJQ

Professional Stall Cleaning Techniques.

Cleaning stalls is a horse-keeping chore that is often times looked at as being menial or unimportant. In reality that couldn’t be less true. A dirty stall or improperly “mucked” stall can result in many health issues for the equine occupant.  Thrush, Cellulitis, breathing and skin problems can be the result of an extended stay in a dirty environment.  Today’s blog will attempt to go over the basics of a good stall management program. This is a topic that is very basic, but sometimes overlooked by training professionals when teaching students horse care and management.

Stalls should be cleaned on a daily basis. On the racetrack where horses are confined in their stalls for 22-23 hours a day, we clean continually throughout training hours. This does seem to lessen our workload in the mornings and does keep the stalls cleaner and drier. Good stall management also involves keeping the stalls maintained structurally. Fix boards and remove anything that poses a risk of injury. Keep the stall floor level and uniform, fill in holes and uneven surfaces with ag-lime, (make sure you "tamp", water and allow it to dry.), mats are an option if a horse puts a lot of wear and tear on the stall floor. Now for the actual cleaning suggestions...

The first step in cleaning a stall is to sift out the manure with a cleaning fork. Some horses have a regular routine and defecate in the same spot or pattern everyday, this makes it easy to clean and assess if all is normal with your horse. Some spread their manure all over the stall; this takes more time to clean and may involve using a rake as a sifting tool for smaller pieces of manure.

Raking the stall usually helps in pinpointing the urine spot, a wet area that will usually be in the same location everyday for each individual horse. 

Fillies and mares tend to urinate toward the back of the stall and colts and geldings tend to urinate toward the center of the stall.  Once you locate the urine spot it is important to remove all the urine soaked shavings down to the mat or limestone base this will help to prevent bacterial infections, such as thrush, and/or ammonia vapors from building up to unhealthy levels. Rake to get as much as possible. Spread the remaining clean shavings throughout the stall in a uniform manner and add more bedding if needed.

For cleaning stalls with straw bedding the process is basically the same except you need to separate the clean straw (usually I use a corner) and remove the manure and soiled straw. Rake the entire base or floor of the stall. Spread the clean straw evenly and add straw if needed.

It's better to bed on too much straw/shavings than not enough. Hock sores, front ankle abrasions and urine stains on the horses will appear if you don't use enough bedding whether you use straw or wood shavings.

Finally, don’t forget to clean feed tubs and water buckets!