Bone Spavin in the Icelandic Horse

How much do you know about spavin in the Icelandic horse?  Take the following quiz to find out.  And read the article below for detailed information.


1. Research studies have shown prevalence rates of spavin as high as ____ among Icelandic horses:
a. 11%
b. 23%
c. 46%
d. 64%
2. Spavin is associated with which joint?
a. hock
b. stifle
c. fetlock
d. pastern
 3. Which of the following can be a sign of spavin?
a. Heat in the joint
b. Back pain
c. Dragging of the hind toe
d. Cracking or popping noise from the joint
e. All of the above
4. Per the Western College of Veterinary Medicine, bone spavin is diagnosed as the most frequent cause of lameness in horses.  True or False?

5.  Per the Merck Veterinary Manual (n.d.), bone spavin is prevalent in the Standardbred and Quarter Horse breeds.  True or False?
6.  Examination of horse bones found in pagan graves in Iceland prior to 1000 AD show that spavin was rare in the Icelandic horse at that time.  True or False?
7.  Per a study by Björnsdóttir et al (2003), the most frequent reason for culling the Icelandic horse in Iceland was hind limb lameness.  True or False?
8.  Which of the following are not risk factor for spavin? (multiple answers):
a. Age
b. High leg action
c. Sickle hocked
d. Frequent use of shoes with outside trailers
e. Breaking to saddle at age 4 as opposed to age 6
9.  Björnsdóttir (n.d.) states that genetic predisposition for spavin is the most important causal factor for the disease among Icelandic horses.  True or False?


10.  Since 2006, FEIF requires that owners of stallions and mares must provide radiographs of the hocks from four different angles from at least age five at the first breeding evaluation.  True or false?
Answers are at bottom of posting.

Introduction
Spavin is probably a term with which many Icelandic owners are unfamiliar.  However, an internet search on the term “bone spavin” delivers many research articles about this disease and the Icelandic horse.  Based on radiograms of horses in Iceland and Europe, results indicate prevalence rates of spavin as high as 46 % in horses across a range of ages.  
Photo from Wikipedia


In this article, I survey the research literature to define what is spavin, describe early symptoms of spavin, scan research on spavin in the Icelandic horse breed, list risk factors for spavin, describe FEIF actions to limit spavin in the breeding population, and highlight success by one breed society in controlling this disease.

What is It?

The Merck Veterinary Manual (n.d.) defines bone spavin as “osteoarthritis or osteitis of the hock joint, usually the distal intertarsal and tarsometatarsal articulations, and occasionally the proximal intertarsal joint. Lesions involve degenerative joint disease, particularly on the craniomedial aspect of the hock with periarticular new bone proliferation, which eventually leads to ankylosis. Although bone spavin usually causes lameness, this may be obscured if the lesions are bilateral. “

Let’s try to explain spavin in layperson’s terms.  The hock or tarsus is in the hind leg of the horse, 

Location of hock--Photo Wikipedia
above the cannon bone; the fetlock is below the cannon bone.  The hock corresponds to the human ankle but bends in the opposite direction.  It is made up of six tarsal bones and four joints.  The tarsocrural is the topmost joint and has the most range of motion (90%).   The other three joints have much less motion but can experience considerable torsion due to the movement of the leg.  Bone spavin usually affects the two lowest joints of the hock: the distal intertarsal (DIT) and tarsometatarsal (TMT) joints.  The third joint, proximal intertarsal, is very unlikely to develop bone spavin (Hanson & McCain, n.d.). 

As Bercier et al (2009) explain, “When wear and tear of a joint occurs, physical and biochemical damage is inflicted upon the articular [joint] cartilage. Enzymes and other agents from the joint lining (biochemical agents) are released inside the joint and destroy the components of the cartilage, triggering tissue inflammation which, in turn, causes pain, effusion, and reduced range of motion. As the cartilage in the joint erodes due to this cyclic insult to the joint, the bones of the joint begin to grind against each other, resulting in further disability and pain.”  When the joint is continually overloaded through uneven wear, bone spurs can also develop.

Bones in the hock--Source
Wikipedia
Spavin is also known as Degenerative Joint Disease (DJD) of the hocks.  In its simplest terms, bone spavin is arthritis of the two lowest joints of the hock. The condition can be quite painful causing the horse to alter its gait, to change the way it moves resulting in back pain, and even to refuse work such as jumping or going downhill that the horse previously did willingly.  If spavin is bilateral or occurs in both hocks, the lameness may be masked since equal amounts of pain occur in each hind leg.  Over time, the two joints may naturally fuse (ankylosis)--which can reduce or eliminate the pain.  The condition can require veterinary care and medical, possibly surgical, treatment (Novick, 2004).

Signs of Spavin

Depending on the severity of the onset of bone spavin, the horse may exhibit any of these signs of the disease (Merck Veterinary Manual, n.d.; Bercier, et al, 2009; Bone spavin fact sheet, n.d.; Shoemaker, 2004):

-          Dragging of the hind toe
-          Shortening of the forward motion of hind hoof
-          Less hock action
-          Elongation of heel
-          Habit of resting toe on the ground with heel raised
-          Lameness that disappears after exercise but returns after stall rest
-          Stumbling
-          Swelling around the joint that last more than two weeks
-          Fluid in the joint
-          Heat in the joint
-          Back pain related to unevenness of gait
-          Unwillingness of horse to back up, turn suddenly, or go downhill
-          Reluctance to take a specific lead
-          Change in behavior such as bucking after jumps or refusing jumps
-          Cracking or popping noise from the joint when used (crepitus)

Many of these symptoms can also be the result of an injury, poor fitting tack, or an entirely different disease.  It is easy to see how an owner can be frustrated and spend considerable time and money tracking down the cause of these non-specific symptoms. 

If you notice significant changes in your horse’s gaits or performance that lasts more than a few

Light exercise can help extend the
working life of a horse with spavin
weeks, check with your veterinarian for palliative treatment.  Confirmation of spavin requires radiograms of the affected joints.  Multiple treatments—from drugs, injections, and surgery-- are available to mitigate the pain.  Corrective shoeing can help.   “However, even with careful management, bone spavin will progressively get worse, and the animal may not be able to continue at the level of competition it was first used for once the lameness is consistent. However, many horses can still be successful in a less-strenuous career. Frequent, light exercise is much better than no exercise at all, and a change of career may prolong the horse's useful life” (Bone spavin fact sheet, n.d.).

Spavin in Other Breeds

Individual horses from all breeds can develop bone spavin.  Dr. Shoemaker, DVM, (2004) reports 

Western reining horse coming to a slinding stop.
This maneuver can  be very wearing on the hocks.
Photo Wikipedia
that “Bone spavin is the most common hindlimb lameness diagnosed at the Western College of Veterinary Medicine [in Canada] and ranks second only to navicular syndrome (caudal heel pain) as the most common lameness diagnosis in the horse…Osteoarthritis is widely recognized as a significant source of lameness in all disciplines of horse use, although the disease is more often associated with mature performance horses that practice jumping or western performance horses used for reining, roping, barrel racing, or cutting.”  

Trauma or repetitive stress can increase the possibility of developing spavin.  As Dr. Novick (n.d.) states, “Among all the sports medicine problems faced by the horse, bone spavin is probably the most common. It affects jumping and dressage horses, trail horses, endurance horses and backyard horses.”  And osteoarthritis or bone spavin is commonly diagnosed as the horse ages.  Dr. Shoemaker (2004) goes so far as to claim that any horse ridden at a fast gallop is at risk for this disease.

Information about actual spavin rates per horse breed is scarce.  The Merck Veterinary Manual (n.d.) mentions that bone spavin is prevalent in the Standardbred and Quarter Horse breeds; prevalence rates are not listed.  In her overview of research on bone spavin in the Icelandic horse, S. Björnsdóttir (n.d.) cites studies in which radiographs have confirmed signs associated with bone spavin in German sports horses, young trotters, and Dutch warmblood foals but she does not list actual spavin rates.  In their study, Björnsdóttir et al (2000) calculate that the percentage of Icelandic horses showing signs of bone spavin as confirmed by radiograms is similar to a study of German riding horses and that the calculated heritability factor of bone spavin is close to that shown by a study of Standardbred trotters in Norway.  Because of the multiple factors involved, they caution that “heritability estimates for lameness need therefore to be interpreted with care.”

However most of the breed specific research that I found on bone spavin relates to the Icelandic horse.  This could be because the Icelandic breed has been genetically pure for 1000 years and there are easily accessible and extensive breeding records available to researchers.  Or it may be that recent research has shown that bone spavin is an inheritable factor among Icelandic horses.

Historic Evidence

Before the conversion to Christianity in 1000 AD, important people in Iceland were sometimes 
Horse remains from Norse burials, in this case from
Sutton Hoo, can provide important evidence about
the historic prescene of spavin in the Icelandic horse.
Photo from Wikipedia
buried with horses sacrificed to the Norse gods.  Björnsdóttir, et al (2004) examined horse bones recovered from pagan graves in Iceland.   The researchers examined the bones for evidence of conformational defects and bone disease.  Out of the 23 grave sites studied, 10 of the horses exhibited signs of various diseases such as splints; 7 of the 10 had obvious signs of bone spavin.  The researchers could not determine the ages of the horses but hoped to determine the ages based on teeth preserved from the graves at some future time.  As the researchers conclude, “It is, however, an interesting observation that both diseases [bone spavin and splints] were also common in Icelandic horses 1000 years ago when the use of the horses for riding and many other environmental factors were very different from now.”  

Research

Around 1985, Sweden began importing large numbers of Icelandic horses from Iceland.  Over the next decade, Icelandic horses became increasingly popular as the horse population grew from around 1000 to more than 10000.  At the same time, Swedish veterinarians noticed that they were treating more and more Icelandic horses for hind limb lameness.   Radiograms confirmed the lameness was due to bone spavin.  This observation kicked off a number of large clinical studies in Sweden and Iceland as to prevalence, risk factors, heritability, progression, and treatment of spavin in the Icelandic horse (Eksell, 2004).   A few of these studies are summarized below.

Eksell et al (1998) conducted a field study to examine the radiographic signs of bone spavin in the Icelandic horse population in Sweden.   They studied 379 Icelandic horses located across 11 farms in Sweden.  The horses ranged in age from 0 to 19; the mean age was 8.1 years. The researchers radiographed the tarsi of all horses and inspected the conformation of each horse.  As confirmed by radiographs, signs of bone spavin were found in 23% of the population.  The rate increased to 33% for horses between the ages of 4 and 8; the study found no signs of bone spavin in horses less than 5 years of age. 

In a study of 508 horses in Iceland, Björnsdóttir et al (2000) found that 46% of the horses showed signs of bone spavin as confirmed by radiograms or indicated by flexion tests of the tarsus.  The researchers deliberately included offspring from 17 evaluated and popular breeding stallions.  Owners submitted data from offspring from additional 83 stallions.   Horses with radiographic signs of spavin were 4 times more likely to be lame. 

Unlike the study by Eksell, et al (1998), Björnsdóttir et al (2004) found signs of bone spavin among Icelandic horses ages six months to six years.  Signs of early onset of the disease were observed in 33% of the tarsal joints that were examined via slab sections.  Since so many of the young stock showed early signs leading to bone spavin, the researchers concluded that the onset of the disease is early with few clinical signs and that it progresses slowly.  Since none of the horses studied had been broken to saddle, the cause of the onset of the disease is unrelated to riding the horse.  As they concluded, the development of the early signs of bone spavin in young Icelandic horses “seems to be due to poor conformation or joint architecture rather than trauma or overloading.”

Spavin is the most common reason for culling the Icelandic horse in their native country.  In a follow up study of 508 horses in Iceland after 5 years, Björnsdóttir et al (2003) surveyed the owners to see which horses had been culled (no longer used for riding).  Those owners who responded to the follow up study reported that 19% had been culled, 30% had been sold or selected for breeding, and 51% were still being used for riding.  Hind limb lameness (42 horses) was the most frequently mentioned reason that the horse was culled.  Other medical reasons for culling were problems with forelimbs and back pain (11 horses), colic (3), digestive infection (1), tumor (1), and laminitis (1).  Other reasons included accidents (12), bad temperament (16), and poor performance (11).  Note the decision for culling in Iceland is usually made by the owner without input from a veterinary.  If the horse had showed signs of spavin in the earlier study, it was less likely to have been sold or used for breeding. As Björnsdóttir et al (2003) point out, “The late clinical manifestation of bone spavin in Icelandic horses may prevent natural and artificial selection against the disease and be an important reason for the high prevalence in the population.”

Risk Factors

Veterinary science and research have determined several risk factors that are related to the
Improper trimming of the horse can lead
to the development of spavin; proper
shoeing can extend the useful life of the
horse.
development of bone spavin in the general horse population.  Age is a major factor.  Like the development of arthritis in humans, the older the horse, the more likely it is to develop this disease.  Another major risk factor involves poor conformation.  The conformational defects of sickle hocked and cow hocked result in uneven loading of the joints and thus increased risk of developing spavin.  Uneven trimming or shoeing of the horse over time is also a risk factor.  (Bone spavin fact sheet, n.d.)  Frequent use of shoes with outside trailers or calks can lead to the development of bone spavin (Shoemaker, 2004). 

Any activity that regularly overstresses the hocks puts the horse at increased risk of spavin.  “Types of activities, such as dressage, show jumping, hunting and racing, which require much hock flexion or where there may be excessive concussive forces acting on the hock joints, may contribute to uneven or repeated loading of the lower hock joints, and thus bone spavin”  (Bone spavin fact sheet, n.d.)

Several research studies have examined risk factors specific to the Icelandic horse.  Björnsdóttir (n.d.) summarizes these risk factors:
-          As horses age, their chances of developing bone spavin increase approximately 6% each year from ages 6 to 12


-          Horses with larger tarsal angles have lower prevalence of spavin probably since the reduced angle alters the biomechanics of the tarsal joints


-          Horses born in the north and south of Iceland had a lower rate of spavin compared with other areas of the country. “This is most likely an indirect genetic effect because of clustering of dams in the specific regions.”


-          Certain sires had significantly higher (or lower) prevalence of bone spavin in their offspring supporting the genetic predisposition of this disease.


-          Workload as indicated by age of breaking to saddle at age four versus age six and entry into stud shows did not impact the prevalence of bone spavin.


-          The mean height for sound horses as measured at the croup was six mm higher than for lame horses as measured by flexion tests.  Although this difference was statistically significant, the researchers regarded the height difference to be too small to be of value.

Although research shows that taller horses may show
better results during flexion tests for spavin, the results
are too small to be of value.

-          Four-gaited horses showed significantly less signs of lameness during a flexion test than five-gaited horses; however the researchers caution that the ability to perform a flying pace may be impacted by the onset of bone spavin therefore artificially reducing a five-gaited horse to a four-gaited horse.

-          Neither the use of a professional versus an amateur trainer, ability to tolt, temperament, or action of the front limbs impacted the prevalence of bone spavin.

As Björnsdóttir (n.d.) summarizes, “The genetic predisposition for the disease stands out as the most important aetiological [causal] factor. It was presumed that the presence of RS [radiographic signs] is a quantitative threshold trait with an underlying normal distribution of multigenetic effect. The genetic contribution can be, at least partly, via the conformation of the hock or the shape of the distal tarsal joints. It is suggested that the medium high heritability estimate reflect an inheritent variation in conformation or stability of the distal tarsal joints, resulting in predisposition to the disease.”

FEIF Guidelines

In 2006, FEIF published rules aimed to reduce the prevalence of inheritable spavin among the Icelandic horse population.  At the first breeding show, the owner of the stallion must provide radiographs of the hocks from four different angles from at least age five.  This radiograph is examined by selected veterinarians in each country for signs of spavin.  The results are recorded in World Fengur. 

Sample spavin report from World Fengur
As the FEIF rules explain, “Breeding selection based on radiographic examination of the distal tarsus is therefore expected to reduce the prevalence of bone spavin in the population. It is most important to exclude stallions and mares that develop RS [radiographic signs] early in life as they are likely to have the highest predisposition for bone spavin” (FEIF, 2006). Readers can refer to the FEIF website for a more complete description of the requirements for submitting radiographs for bone spavin at breeding shows.  

Per my article in the Fall edition of the USICH Quarterly:  “Dr. Nathan Dykes, Senior Lecturer, Section of Veterinary Imaging, in the College of Veterinary Medicine at Cornell University, has been engaged by FEIF to interpret the required radiograms submitted by horse owners as part of the breeding evaluation process for Icelandic stallions.  He explains that ‘In a small sample of Icelandic horse radiographs examined at Cornell, the incidence of osteoarthrosis of the tarsus (“bone spavin”) is low. Sample bias may falsely lower the true prevalence of spavin in this breed. ‘ 

‘As far as the true prevalence of spavin in the Icelandic horse, I don’t believe that I have examined a large enough sample. Further, I am only sent those radiographs taken by other veterinarians on horses not lame. I don’t examine tarsus radiographs from lame horses or radiographs that may be diagnosed with spavin by the primary veterinarian. This is why my sample is likely biased. If you wanted to get a true prevalence, you would need to examine all horses, sound and lame and not select only the studies from the “good ones” to put into the stud book. There are many examples of this bias in the veterinary literature. Breeders are probably unwilling to submit the radiographs from horses with signs of spavin so those stallions don’t get counted and their veterinarians can easily see the signs of spavin so may advise them ahead of time not to submit the exam.’"  (Nolf, 2013)

Success Story

Officials of the Dutch Warmblood society were alarmed at the relatively high prevalence (5%) of

Dutch warmblood performing at
World Cup--Wikipedia
spavin in their breed in the early 1980s.  Studies of the Dutch Warmblood in that timeframe showed that there was a strong correlation between poor conformation of the hock (especially sickle hocks, extended hocks, outward rotation of the hock) and the incidence of spavin.  Other researchers estimated that the heritability of bone spavin in the Dutch Warmblook was between 0.20 and 0.35, meaning that a stallion with inheritable spavin would sire 1.6 times more offspring with this disease than a sire who did not carry this trait.  (Barneveld, 2004)

By strengthening the conformation standards and requiring radiograms for approved breeding stallions in the Royal Dutch Warmblood Studbook (KWPN), the society reduced the prevalence of bone spavin in the breed from 5% to less than 1 %. “In fact, nowadays bone spavin can be considered a rare disease in the riding horse that hardly plays a role in pre-purchase examinations” (Barneveld, 2004). This success story can certainly serve as an inspiration to Icelandic horse breeders.

Moving Forward

FEIF has taken an excellent first step to reduce the incidence of spavin in the Icelandic horse population by requiring radiograms of breeding stallions.  The results published on World Fengur provide useful data that you can take into consideration when selecting a younger stallion to breed to your mare.  If you are thinking of breeding to a stallion who is not evaluated or whose evaluation pre-dates 2006, World Fengur may provide the names of owners of the stallion’s offspring whom you can contact to discuss occurrence of spavin.  And if you are purchasing an Icelandic horse, you can take the same steps.  When selecting a horse you will want to pay particular attention to those conformational defects—such as sickle hocks and cow hocks--- associated with early onset of spavin.   If you are concerned about how spavin may impact the long-term rideability of your investment, you can talk to your vet about taking radiograms as part of the pre-purchase exam.  Let us all look forward to the time when spavin in the Icelandic horse, just as in the Dutch Warmblood, need no longer play a role in pre-purchase examinations.     

Answers to Quiz:

  1. C
  2. A
  3. E
  4. False.  Per Western College of Veterinary Medicine, navicular syndrome (caudal heel pain) is the most common lameness diagnosis in the horse; spavin, the second most frequent diagnosis.  However, spavin is the most common diagnosis of hind limb lameness. 
  5. True.
  6. False.  Horse bones found in pagan graves indicate that splints and spavin was fairly common among Icelandic horses at that time.
  7.  True. 
  8. B, E
  9. True
  10. False.  FEIF only requires owners of stallions to provide radiograms of the hock. 
References:
Barneveld, A.  (2004).  Bone Spavin, a Dutch View.  International Symposium on Diseases of the Icelandic Horse, International Veterinary Information Service.

Bercier, S., Burba, D., Heidorn, N.  (2009).  Bone spavin.  Found March 5, 2013 at http://text.lsuagcenter.com/en/crops_livestock/livestock/Horses/Lameness/Bone-Spavin.htm

Björnsdóttir, S.  (n.d.)  Bone spavin in Icelandic horses.  Icelandic Veterinary Services, Dep. Holar 551 Saudarkrokur, Iceland

Björnsdóttir, S., et al.  (2000).  The heritability of degenerative joint disease in the distal tarsal joints in Icelandic horses.   Livestock Production Science 63, pp. 77-83.

Bjornsdottir, S., Ekman, S., Eksell, P., and Lord, P.  (2004).  High detail radiography and histology of the centrodistal tarsal joint of young Icelandic horses. Equine Veterinary Journal 36 (1) pp. 5-11.

Björnsdóttir, S., Jörundsson, E., Arnadóttir, L., (2004).  Bone Diseases of the Saga Horse – A 1000 Years Old Story.  International Symposium on Diseases of the Icelandic Horse, Veterinary Information Service.

Björnsdóttir, S., Árnason, T., Lord, P. (2003). Culling Rate of Icelandic Horses due to Bone Spavin.  Acta Vet Scand. 44(4): 161–169.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1831549/

Bone Spavin.  (n.d.)  The Merck Veterinary Manual.  Found at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/90771.htm

Bone spavin fact sheet.  (n.d.).  The Dick Vet Equine Practice.  University of Edinburgh.

Eksell, P.  (2004).  Bone spavin in Icelandic horses - Diagnostic imaging and long term follow up.  International Symposium on Diseases of the Icelandic Horse, International Veterinary Information Service.

Eksell, P., et al (1998).  Prevalence and risk factors of bone spavin in Icelandic horses in Sweden: a radiographic field study.  Acta Vet Scand. 1998;39(3):339-48.  

FEIF.  (2006)  New rules aimed to reduce the prevalence of bone spavin in Icelandic horses.  Last found March 10, 2013 at http://www.feif.org/Download/Breeding/tabid/204/Default.aspx

Hanson, A., & McCain, R. (n.d.).  Bone spavin.  Found March 1, 2013, at http://evrp.lsu.edu/healthtips/bone_spavin.htm

Nolf, P.  (2013).  Bone Spavin, USIHC Quarterly.

Novick, D. (2004).  Hock lameness - bone spavin.  Found March 5, 2013, at http://www.novickdvm.com/spavin.htm

Shoemaker, R.  (2004).  Osteoarthritis of the distal tarsal joints (bone spavin) in the horse.  Large Animal Veterinary Rounds, Volume 4, Issue 2, pp. 1-6.


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