By Popular Demand: Here’s How You X-Ray for the C6-C7 Malformation

News about the malformation of the C6 and C7 vertebrae has understandably raised a lot of concern. There are major implications for both buyers and breeders of TB and TB-derived breed horses, as outlined in the original article, All You Need to Know About the Hidden C6-C7 Malformation That’s Bringing Horses Down. In response, Sharon May-Davis has very kindly provided us with the English version of a paper she published in the Journal of Japanese Local Government Racing, outlining a preliminary protocol for radiographing this area of the neck and identifying the malformation. (Yes, a single racing authority has taken this issue on board!)

So without further ado, here is the paper in its entirety, the only adaptations being the positioning of images to better fit this site’s blog format.

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Preliminary Radiographic Protocols for Identifying Congenital Malformations of the Caudal Cervical Vertebrae

Authors: May-Davis SER, Minowa F, Monoe S



In 2014, a published study based on dissections and skeletal examinations noted that 19:50 Thoroughbred horses had a congenital malformation of the 6th cervical vertebra (C6). In addition, it was found that in those 19 Thoroughbred horses expressing a congenital malformation of C6, 9 displayed a concurrent congenital alformation of the 7th cervical vertebra (C7). In this study, 3 Thoroughbred horses and 1 Thoroughbred type were clinically examined; 3 were radiographed for limb abnormalities and 2:3 radiographed for the congenital malformation of C6 and C7 prior to euthanasia. Upon dissection, 3:4 expressed a congenital malformation of C6 with 2:3 displaying a concurrent CM of C7. These 2 horses were positively radiographed for the CM of C6 and C7 prior to dissection. The radiographs of C6 were taken in direct lateral orientation with 0 degree of elevation and revealed the absence of the caudal ventral tubercle (CVT) of C6. Re-positioning the horse’s forelimbs caudally with an outstretched neck, C7 was radiographed at a 30° oblique lateral angle in a cranial to caudal direction with 0 degree of elevation; the transverse process of C5 remained cranial to the beam. The caudal aspect of the plate was positioned medial the Cranial deep pectoral and rotated vertically to expand the field of view of the cervical vertebrae, whilst remaining perpendicular to the beam



In recent times, 3 Australian studies reported congenital malformations of C6, C7, the 1st sternal rib, along with their associative soft tissue structures. Furthermore, it was noted that these congenital malformations were predominantly breed related and more specifically, to Thoroughbred horses or derivatives thereof. In addition, reports of forelimb proprioceptive dysfunction, neurological impediment and gait deficits were concurrently noted (May-Davis [a,b], May-Davis and Walker). The congenital malformations of C6 appeared as either a left or right unilateral absence of the caudal ventral tubercle (CVT) or as a bilateral absence of the CVT (Figure 1).


Left: Normal. Centre: Absent right CVT. Right: Bilaterally absent CVT

Figure 1. View of the ventral aspect of C6, cranial aspect top. Photo credit: Sharon May-Davis


The congenital malformation of C7 appeared with either a fully transposed CVT from C6 onto the ventral surface of C7 or a partial transposition of the CVT from C6 onto the ventral surface of C7 (Figure 2) (May-Davis [a]).


Left: Normal. Centre: Transposed right CVT. Right: Bilaterally transposed CVT

Figure 2. View of the ventral aspect of C7, cranial aspect top. Photo credit: Sharon May-Davis


The congenital malformation of the 1st sternal rib appeared in multiple presentations with gross anatomic variations including; an absent 1st sternal rib; bifid Tuberculum costae (Figure 3); bifid Sternochondral articulation onto the sternum; flared shaft; normal 1st sternal rib inserting onto the cranial branch of a bifid Sternochondral articulating 2nd sternal rib; straight costal shaft and an articulating rudimentary Tuberculum costae with a ligamentous extension replacing the bony shaft and attaching to a rudimentary Sternochondral articulation onto the sternum (May-Davis [b]).

Figure 3. Left costal bifid Tuberculum costae. Photo credit: Sharon May-Davis

Associative soft tissue structures varied according to the presentation of the congenital malformation with the most noted being, the Longus colli muscle, Scalene muscles and neural vessels such as the Phrenic nerve and Brachial plexus (May-Davis [b], May-Davis and Walker).

The congenital malformations noted in these 3 studies were determined via dissection and skeletal examination. They were based on 2 specific skeletal variations in C6 and C7 plus any variation to normal of the 1st sternal rib.

The congenital malformations could appear in C6 as a singular expression with no other anomalies, however, the congenital malformation of C7 only occurred when the CVT was absent on C6. The congenital malformations of the 1st sternal rib only occurred in the presence of the congenital malformation of C6 and C7 (Table 1) (May-Davis [b]).

With this in mind, the premise that if a congenital malformation exists in C6 then there is a 50% chance that transposition will occur on C7. In this format, it would stand to reason that there could also be an anomalous rib. Therefore, this study is designed to identify the absent CVT on C6 and investigate its transposition onto C7.


Table 1. Noted observations of 151 horses of mixed gender aged between 0 (stillborn) and 30, exhibiting a congenital malformation of C6, C7 and the 1st sternal rib.


Materials and Methods

After evaluation and clinical examination, the 2 horses (1 Thoroughbred and 1 Thoroughbred type) were restrained in cross ties. Detomidine Hydrochloride (Detomovet CEVA Animal Health Pty Ltd) was administered via left jugular vein venepuncture. The dosage was determined by the clinician’s experience and in consideration of the individual’s current health status.

The radiographs were obtained by utilising a Porta 100 HF High Frequency portable x-ray unit (7.8kgs). The kV range was 40-100kV with an mA range of 20-30 mA and a mAs range of 0.3 – 20 mAs. The images were captured on a wireless Rayence 1012WCA Medical Image processing unit (26cm x 32.5cm) and computerised with Vetview Digital Diagnostic Imaging software.

The radiographic angles were obtained with the horse’s neck in full extension and the forelimbs behind the vertical in standing position. With the clinician standing with the x-ray unit on the left side of the neck and the plate positioned on the right side of the neck, the distance between the x-ray unit and plate was 80cms. The x-ray unit and plate remained lateral to the cervical vertebrae determined by the transverse processes of C5.

The first view is a direct lateral at 90 degrees, with 0 degree of elevation whilst maintaining the transverse process of C5 to the left of the beam. 

Remaining lateral to the cervical vertebrae with a 0 degree of elevation, the second view is taken with the x-ray unit positioned at a 30° oblique lateral angle in a cranial to caudal direction with the transverse process of C5 cranial to the beam. The caudal aspect of the plate is positioned medial the Cranial deep pectoral and rotated vertically to expand the field of view of the cervical vertebrae, whilst remaining perpendicular to the beam.

Upon the radiographic evaluation of C6, radiographs of C7 are obtained. The 4 horses were then euthanized and dissected so to verify the radiographic findings. Only those pertaining to the congenital malformation of C6 and C7 are reported in this study.



Figure 4. A compressed trachea (white arrow) in Thoroughbred No. 2 at C6 / C7. Photo credit: Sharon May-Davis

Upon euthanasia of the 4 horses, Thoroughbred No.1 was normal. Thoroughbred No.2 presented with an absent CVT in C6 and trachea compression (Figure 4).

Thoroughbred No. 3, presented with a C6 and C7 congenital malformation and a malformed 1st sternal rib. The Thoroughbred type also presented with a congenital malformation of C6 and C7 (Table 2).



Table 2. Noted observations via dissection of the congenital malformation of C6, C7 and the 1st sternal rib.


Left: Radiographic view of C6. Centre: The white line denotes a normal CVT. Right: The white denotes an absent CVT.

Figure 5. The radiographic lateral view of C6 depicting a unilaterally absent CVT in C6. Image credit: Sharon May-Davis


Thoroughbred No. 3 C7 radiograph (Figure 6) clearly presents the observer with a transposition of the CVT from C6 onto the ventral surface of C7, furthermore it denotes a reciprocal deviation in the trachea at the point of this transposition.


Left: Radiographic view of C7. Centre: The white line denotes the unilateral transposition of the CVT from C6 onto the ventral surface of C7. Right: The white line denotes the deviation in the trachea.

Figure 6. The radiographic view of C7 depicting a unilaterally transposition of the CVT from C6. Image credit: Sharon May-Davis


The Thoroughbred type (Figure 7) exhibits the absent CVT in C6. The radiograph clearly indicates an absent CVT that is unilateral in its presentation.


Left: Radiographic view of C6. Centre: The white line denotes a normal CVT. Right: The white denotes an absent CVT.

Figure 7. The radiographic lateral view of C6 depicting a unilaterally absent CVT in C6. Photo credit: Sharon May-Davis.


The Thoroughbred type C7 radiograph (Figure 8) clearly presents the observer with a transposition of the CVT from C6 onto the ventral surface of C7, furthermore it denotes a reciprocal deviation in the trachea at the point of this transposition.


Left: Radiographic view of C7. Centre: The white line denotes the unilateral transposition of the CVT from C6 onto the ventral surface of C7. Right: The white line denotes the deviation in the trachea.

Figure 8. The radiographic view of C7 depicting a unilaterally transposition of the CVT from C6. Photo credit: Sharon May-Davis.


Figure 9. Right: Absent CVT on C6 (white arrow) and transposed CVT from C6 onto the ventral surface of C7. Photo credit: Sharon May-Davis

Upon dissection, the Thoroughbred type displayed identical congenital malformations of C6 and C7 as depicted in the radiographs (Figure 9).







This study was conducted with the view to obtain specific radiographic evidence of the congenital malformation of C6 and C7. Radiographic views of the 1st sternal rib were not possible due to thick and dense musculature in the region. The views obtained of C6 and C7 with exact radiographic angles proved that this region can be radiographed with precision so that the practitioner can make a clear diagnosis should a horse present with a neurological deficit, as previously published (May-Davis

[a, b], May-Davis and Walker]). Furthermore, the asymmetry of the cervical vertebra could exacerbate arthritis in the articular process joints as previously noted (May-Davis [a]). In addition, the incidental finding of the compression of the trachea is an important factor to consider when Thoroughbred racehorses present with compromised airways. An explanation for this occurring is that the Longus colli muscle hypertrophies in support of the weakened structures and due to its proximity to the Trachea, it impinges upon its dorsal surface. This impingement is further exacerbated by the ventral projection from C7 of the transposed CVT from C6.

Since the first publication in 2014, retrospective studies were conducted that added another dimension to the current research. Italian and American studies noted that Warmbloods, Quarter Horses and Arabs were also afflicted with this condition (Santinelli et. al 2016 and DeRouen 2016). It is significant to note that these breeds present the majority of the ridden horse population in Japan extending from Racing, Showjumping, Dressage to Eventing and Endurance. However, a specific Dutch Warmblood study was conducted with fresh cadaver’s that were portioned and CT scanned (Veraa 2016), this also included Oldenburg horses. The congenital malformation of C6 and C7 was present in both breeds with a noted malformed 1st sternal rib in a Dutch Warmblood. Combined percentages of these 3 studies in conjunction with the 3 Australian studies and the current study has the congenital malformation of C6 at; Warmbloods 30%, Quarter Horses 16% and Thoroughbred horses over 40%. 

Aside from the Arabian who is an ancestor to the Thoroughbred, the Warmblood breeds and Quarter Horses all have Thoroughbred lineage in the back line of their breeding. Thus, implying that this condition is heritable as noted by May-Davis [b] and more systemic than just one breed. With this in mind, all critical events should be assessed with the knowledge that a potential congenital malformation could exist in C6, C7 and the 1st sternal rib, as previously noted. With the largest population of horses in Japan being Thoroughbreds, it would be a recommendation to note the studies of several countries including Japan and the severity in percentage of this systemic congenital malformation. Especially in relation to Thoroughbred’ racehorses racing and cornering at speed.



This study showed that of the 4 horses investigated, 3:4 horses displayed a CM of C6, 2:3 displayed the congenital malformation in C6 and C7, and 1:2 a congenital malformation of the 1st sternal rib. Even with a small sample of Thoroughbreds, studies from other countries must be measured and it would therefore be a recommendation to radiograph for this condition in the caudal cervical vertebrae in a pre-purchase examination. The purpose of which would be to eliminate this condition so that riders and handlers are not put at risk.


Author contributions

Sharon May-Davis, Fumiko Minowa and Sadae Monoe wrote and reviewed this article.


Conflict of Interest

The authors have no conflict of interest in the preparation or presentation of this original research article.



The author wishes to thank Christine Gee for her professional advice on the manuscript. The Nippon Veterinary and Life Sciences University for the use of their facilities and to those authors / editors/ publishers of those articles, journals and books cited in this manuscript.



Derouen A, Spriet M, Aleman M. Prevalance of anatomical of the sixth cervical vertebra and association with vertebral canal stenosis and articular process osteoarthritis in the horse. Vet Radiol Ultrasound, Vol. 00, 2016, pp 1–5.

May-Davis SER. The Occurrence of a Congenital Malformation in the Sixth and Seventh Cervical Vertebrae Predominantly Observed in Thoroughbred Horses. J Equine Vet Sc 2014; 34:1313-17.

May-Davis SER. The Congenital Malformation of the 1st Sternal Rib. J Equine Vet Sc 2014; 34:1313-17.

May-Davis SER, Walker C. Variations and implications of the gross morphology in the Longus colli muscle in Thoroughbred and Thoroughbred derivative horses presenting with a congenital malformation of the sixth and seventh cervical vertebrae. J Equine Vet Sc 2015; 35:560-8.

Santinelli I, Beccati F, Pepe M. Anatomical variation of the spinous and transverse processes in the caudal cervical vertebrae and the first thoracic vertebra in horses. EVJ 48 (2016) 45–49.

Veraa S, Bergmann W, van den Belt A-J, Wijnberg I, Back W. Ex vivo computed tomographic evaluation of morphology variations in equine cervical vertebrae. Vet Radiol Ultrasound, Vol. 00, 1–7.




8 Golden Rules For Helping Your Thoroughbred Get Right Off The Track

OTTB Header

Sometimes, you can achieve more by doing very little. There’s a lot advice around about what you can do to help ex-racehorses, or OTTBs (Off the Track Thoroughbreds). Much of it focuses on what can be done through retraining, while some of it focuses on dealing with physical issues.

In this guest post, Kerry Warren Couch responds to the recent article about physical issues in OTTBs by stating, clearly and simply, how she has helped her OTTBs over many years, mainly by initially doing very little at all.

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I have ridden many OTTBs over the decades of my riding career, professionally and for sheer pleasure. I just adore them – they have so much heart, and they give  everything if the rider is willing to be extraordinarily patient, partnering with their horse and never forcing them.

I loved the Buying an Ex-Racehorse: Can You Spot the Major Physical Issues? article – it’s absolutely on target. I have a few suggestions for folks to consider when they bring their OTTBs home. These come from my personal experience – they may not apply to everyone and all cases, so do keep that in mind.

The author's new OTTB

The author’s new OTTB

Seven months ago, I purchased yet another OTTB. He came from a top trainer/track and we knew his entire medical history, including x-rays. This is NOT typical – I was very fortunate to have access and for my vet to be able to talk with the stable and their vets. Very lucky me.

Despite coming from a top trainer, my new OTTB does have some issues – he IS an ex-race horse, so this is to be expected.

He has benefited from my usual approach, which helps the horse long before we start work.

What follows is my approach to helping every OTTB that comes to live at my farm.

1. Allow the OTTB plenty of downtime

My OTTBs have always needed time to ‘defuse’ from the training barn life, so I turn them out, slowly to acclimatize – but then as they come to understand turn out, I find them pasture mates and allow turn-out at will, so they can go in their stalls or walk out to the field as they wish.

2. Give the OTTB a full check-up

I have a complete chiro assessment done before ANY work is begun – and that includes groundwork. We start working on the serious physical issues right away, but leave simple ones for a little later, so we don’t overwhelm the horse in his transition to a non-track life.

3. Use paddock time as self-help time

I am lucky that my farm has hills, so I can help my OTTBs work on symmetrical muscle building long before I begin groundwork. I purposefully keep their water in their stalls so they must walk the hills every day, from pasture to barn and back. Their attitudes really change with this time to ‘reprogram’.

OTTB SandI also have a designated ‘rolling area’ near the paddock, filled with super soft sand.  I have been amazed at how smaller, simpler issues can be naturally worked out by allowing horses to relax and roll in lovely sand.

My region has hard clay soil, so I had the sand area made, because I know that rolling on hard clay can actually cause or exacerbate injuries. It’s not that expensive and I’ve found that horses LOVE it. Do consider putting it in a well-drained area with a little bit of full sun, as warm sand is wonderful!

4. Use grooming as therapy time

I groom them every day ­– slowly and methodically.  I fully believe this has wonderful therapeutic benefits. It helps with circulation and muscle tone, and helps me partner with my horses without asking anything of them.

5. Work out an individual nutritional plan

Where feed’s concerned, I have full blood panels done and put a nutrition program together based on each horse’s needs. These vary from horse to horse.

I have been fortunate to acquire OTTBs from known training barns, so my horses typically have few deficiencies. This may NOT be the case for so many people who are purchasing OTTBs from a TB rescue operation or general sale.

By the way, I am NOT implying that rescue groups do not take care of the horses. It’s just that sometimes, the rescue folks aren’t told about the horse’s medical history, so they simply don’t know. It is not due to any lack of care or concern on their part.

Hills at the author's place

Hills at the author’s place

We some times see minor anemia, and imbalance in the micro-minerals.  Many OTTBs do have some signs and symptoms of gastric discomfort. This may reflect fore or hind gut ulcers. I don’t like to have an endoscopy performed, as the pre and post procedures often exacerbate the ulcers, if they do exist.

I actually prefer to treat this area empirically. So, if my vet and I both feel the horse is exhibiting signs consistent with ulcers, we treat them without the instrumental diagnostics.

That said, if there IS a serious issue, one certainly may wish to pursue the endoscopy.

Diet is really individualized to the horse. It is not advisable to suddenly change a horse’s diet. I like to implement a tapering program. I keep the horse on whatever he was being fed at the training barn for two weeks, with a very slow changeover to whatever program we have determined for the new horse.

I typically have acquired very young OTTBs, ie, 3-4 year olds. So I know my horses are still growing and will require nutrition appropriate to a growing horse. We do feed a LOW carbohydrate feed mix and will supplement as warranted. If one feeds the proper amount as recommended by the feed company and one’s vet, the horse ought to receive the right blend of vitamins and minerals.

I do like to add flax seed meal, not the seeds. If a horse has really thin walls or poor feet, I add a hoof supplement with biotin and trace minerals. If a horse requires, we will add probiotics. If a horse is a poor drinker, I may add some soaked, drained, no-molasses-added beet pulp.

I think the main thing here is that no two horses are exactly the same.  There is NO cookie cutter approach to caring for horses. There are only general principles:

  • Fresh, clean water, daily (scrub out those water buckets),
  • Plenty of quality hay and forage at will, so the horse does not stand for hours without roughage (the average 1100 lbs horse requires approx 22 lbs of total quality forage a day, which can be a combination of pasture and hay, all hay or all pasture)
  • Get the horse out, moving at will in a pasture so the fore and hind gut can work effectively.
  • Make sure a dentist has assessed their teeth.
  • A fecal test is also a good idea, especially for OTTBs coming from a rescue or general sale.  Good training barns have a worming routine.  This may not be the case with a rescue operation or at a general sale when one doesn’t know much about the OTTB’s origin.
  • I also know the vaccination history of my newly acquired horses, but this may not always be the case for others.  I’d advise anyone to discuss this with the veterinarian.

6. Improve poor hoof balance slowly

I get the farrier in from the beginning to slowly – NOT rapidly – change those hoof angles over several months of trims.

Most OTTBs have under run heels, long toes and flat soles. A slow correction  allows longer term adaptation of the hoof structures and avoids short term soreness. It also avoids dramatic changes that affect posture

OTTBOne MUST take it very slowly.  I believe this holds true for any horse, but particularly for the OTTBs.  Their muscles, tendons and ligaments are put at risk if angle changes are made too rapidly. It leads to transitory lameness, soreness and increased risk of injury, even in the pasture.

I offer the analogy of a person wearing barn boots, day-in, day-out. Then, suddenly switching to three inch high heels and attempting to carry out the same daily chores. OUCH!

I think it is SO important to have all the professionals involved in the horse’s care/transition on the same page and are informed of each other’s interventions with the horse.  It’s really important to have the big players on the ‘team’ communicating with one another:  the chiropractor, the farrier, the vet/nutritionist, hay and feed dealer.

7. Allow time for slow and steady progress

I have also found that my OTTBs have really needed to learn how to enjoy other horses and life before I start any type of training program.

We humans seem to be in such a hurry.  It’s so helpful to let their bodies and minds defuse.

I have noted that less experienced horse owners would do well to remember that these horses are NOT, at this stage, pets. They have frequently not been cuddled or hand fed carrots, or hugged or loved. These horses were working horses. They had a job to do.

I have observed some people new to horses being so enthralled with the idea of adopting an OTTB that they immediately want to love them, pet them, stand very close to them and even throw their arms around their necks.  This is a lovely sentiment but oh, so dangerous. Ex-track horses are often more accustomed to varied stall muckers coming in, varied groomers, different hot walkers, exercise riders, jockeys, etc.

So many OTTBs are simply NOT accustomed to being fussed. They may pin their ears and toss their heads to even bite or nip at the new owner, raise a hind foot, or wring the tail as a warning. People new to horses who start with an OTTB really really need to be aware of this and put together a realistic plan to allow the horse to defuse, detox, rebuild and SLOWLY re-acclimatize to a life where his new people will show affection.

This happens over weeks or months – NOT days. Take it very slowly and give the horse his personal space and time to come to you – don’t force your eager affection on the horse too soon. It may likely backfire.

In time, with patience and understanding, you WILL have a lovely, affectionate horse. But not right away, as a general rule.

Talking to your horses daily, or singing, is good – I sing a lot to my horses so that they learn my voice and intonations.  I do this over a long period, way before I ever attempt to be affectionate with my new OTTB. And even then, I wait for my horse to show me he is ready for me to rub his ears, etc.

Grooming helps this along, too. I often sing while I groom.

8. Enjoy starting work with your OTTB



With all this, they are so much easier to work with – even for their rehab therapies, and physical therapy is always part of the program. They ARE off the track and there WILL be issues, almost always hips, pelvis, back and others…

I give my OTTBs six full months, and sometimes up to a year, as each horse is different.  I know that may not be reasonable for many people, but even so, at least three months would yield a big benefit.


I do hope others have suggestions to add in the Comments section, below. Horses are such magnificent and amazing creatures.  I have spent my lifetime, to date, with them, and I feel I have merely scratched the surface of understanding. I learn something new every single day.  They are wonderful teachers, if we simply have the heart and open mind to ‘listen’ to their voices. 


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