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In recent years, equine complex vertebral malformation (ECVM) has been of concern in the equine community, with studies identifying numerous associative morphological variations. Here, we examine the morphological association between C6 and C7 for dependency in ECVM cases, where the partially absent ventral process of C6 transposes on the ventral surface of C7. A C6 ventral process presents two tubercles, one cranial (CrVT) and one caudal (CVT). In this study, the C6 osseous specimens ( n = 85) demonstrated a partial or completely absent CVT (aCVT) graded 1-4 that often extended cranially creating a partially absent cranial ventral tubercle (aCrVT) graded 1-3. In the 85 C6 osseous specimens examined, the corresponding C7s demonstrated either a complete or incomplete transposition of the ventral process from C6 in 44/85, with 30/44 replicating a transverse foramen. A strong statistical dependency existed between C6 grade 4 aCVTs and grades 1-3 aCrVTs and C7 transpositions with replicated transverse foramen. Sidedness was also demonstrated, where a left sided absent C6 associated with transposition on the left ventral surface of C7. This likewise applied to right sidedness and most bilateral cases. These findings might benefit practitioners when radiographing the extent of the ECVM configuration in patients presenting caudal cervical pain.

This study examined the anomalous variations of the ventral process of C6 in modern E. ferus caballus. The aim was to provide an incremental grading protocol measuring the absence of the caudal ventral tubercle (CVT) in this ventral process. The findings revealed the most prevalent absent CVT (aCVT) was left unilateral ( n = 35), with bilateral ( n = 29) and right unilateral ( n = 12). Grading was determined in equal increments of absence 1/4, 2/4, 3/4, with 4/4 representing a complete aCVT in 56/76, with a significance of p = 0.0013. This also applied to bilateral specimens. In those C6 osseous specimens displaying a 4/4 grade aCVT, 41/56 had a partial absence of the caudal aspect of the cranial ventral tubercle (CrVT). Here, grading absent CrVTs (aCrVT) followed similarly to aCVTs, though 4/4 was not observed. The significance between 4/4 grade aCVTs and the presentation of an aCrVT was left p = 0.00001 and right p = 0.00018. In bilateral specimens, C6 morphologically resembled C5, implying a homeotic transformation that limited the attachment sites for the cranial and thoracal longus colli muscle. This potentially diminishes function and caudal cervical stability. Therefore, it is recommended that further studies examine the morphological extent of this equine complex vertebral malformation (ECVM) as well as its interrelationships and genetic code/blueprint.

In this study, we examined the ventral process of C6 in extinct and extant Equus (sister taxa to Equus ferus caballus only) with the purpose of describing normal morphology and identifying anomalous variations relevant to recent studies describing a congenital malformation in E. ferus caballus . Overall, 83 specimens from 9 museums and 3 research/educational facilities were examined, totalling 71 extinct specimens from 12 species and 12 extant specimens from 5 species. The lateral view revealed that a large convexity exists in the ventral process between the cranial ventral tubercle (CrVT) and the caudal ventral tubercle (CVT) in the earliest ancestor, Hyracotherium grangeri , from 55 mya, which receded throughout the millennia to become a smaller convexity in E. ferus caballus and the sister taxa. The CrVT is visibly shorter and narrower than the CVT, with a constricted section directly ventral to the transverse process, essentially demarcating the CrVT and CVT. No congenital malformations were evident. As the ventral process of C6 is an integral component for muscle attachment in supporting the head/neck during posture and locomotion, this would indicate that the caudal module in the cervical column might be compromised when a partial or complete absence of the CVT is detected via radiographs in modern E. ferus caballus .

Ultrasound is a well-established modality in equine investigative and diagnostic procedures. Although to date, it has not been utilized in examining the attachments of the equine nuchal ligament lamellae (NLL) onto the cervical vertebrae, for which a noninvasive technique is currently lacking. This study presents a standardized methodology for investigating the equine NLL using ultrasonography, and further evaluates the ultrasound images against postmortem dissection in two nonrelated horses. The ultrasound images in both horses clearly presented the attachment points of the NLL to the dorsal spines of the cervical vertebrae from C2 to C5, whereas no attachment points could be seen from C6 to C7. The ultrasound images were confirmed through close, comparative inspection of the NLL postmortem. Therefore, ultrasound provides a noninvasive alternative to gross anatomic dissections for investigating the NLL attachments in members of the family Equidae. Importantly, this provides an opportunity to examine endangered breeds or isolated populations without the detrimental loss to the gene pool of rare anatomic and or primitive traits., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The Yonaguni pony is a rare breed of pony that has remained isolated on the westernmost island of Japan and may well retain normal morphological traits currently lost in most domestic horses (Equus caballus), such as the attachment of the nuchal ligament lamellae (NLL) from C2-C7. Recent research has found that NLL attachments are no longer present at C6 and C7 in most modern domesticated horses. This study investigated the attachments of the NLL in three Yonaguni ponies; 2 were examined in situ(deceased), and 1 was examined in vivo via ultrasound. The aim was to verify the attachments and compare the morphology to that in equids from previous studies. The in situ (2/2) and in vivo (1/1) findings revealed that the NLL was attached from C2-C7 in the Yonaguni ponies., (©2020 The Japanese Society of Equine Science.)

For over 200 years, equine anatomic literature has chiefly portrayed the attachment points of the nuchal ligament lamellae (NLL) from the second to the seventh cervical vertebrae (C2-C7). However, recent studies have shown that the modern domestic horse, Equus caballus, primarily exhibits the attachments points from C2-C5. Here we present the rare finding of a complete NLL attached from C2-C7 in one Australian Stock Horse (ASH) and discuss the potential implications of these findings. Previously, this trait has only been confirmed among close descendants of Equus ferus ferus; namely the primitive Dutch Konik and Bosnian Mountain Horse. The examination of the NLL attachment points in 55 unrelated horses of mixed breeds revealed that 52 horses had attachments from C2-C5; 1 horse (Welsh Cob) had attachments from C2-C6; and only 2 horses (ASH and Dutch Konik) presented with a complete NLL attached from C2-C7. In light of earlier findings that suggest this loss of NLL attachment at C6 and C7 occurred after domestication, a possible explanation for this finding in 1 ASH is that it is a remnant trait from the founder population of Waler horses that contributed to the early development of the ASH breed. The reported rare occurrence of a complete NLL (C2-C7) in a modern domesticated equine (ASH) suggests that there may be other individuals expressing this unique trait, providing opportunity for its preservation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The 55-million-year history of equine phylogeny has been well-documented from the skeletal record; however, this is less true for the soft tissue structures that are now vestigial in modern horse. A recent study reported that two ligamentous structures resembling functional interosseous muscle II and IV were evident in Dutch Konik horses. The current study investigates this finding and compares it to members of the genus Equus to identify either a breed anomaly or functional primitive trait. Distal limbs ( n = 574) were dissected from four species of Equus ; E. caballus , E. asinus , E. przewalskii and E. quagga boehmi . E. caballus is represented by 18 breeds of horse, including the primitive Dutch Konik'. The interosseous muscle II and IV were evident in all four species, but only two breeds of E. caballus expressed this trait-the Dutch Konik and Bosnian Mountain Horse. These two breeds were the only close descendants of the extinct Equus ferus ferus (Tarpan) represented in this study. In conclusion, the interosseous muscle II and IV originated from the distal nodule of metacarpal II and IV, respectively, and inserted into the corresponding branches of interosseous muscle III proximal to the sesamoids. This suggests a functional role in medial and lateral joint stability and a primitive trait in modern equids.

Conflicting data predominantly describes the equine nuchal ligament lamellae (NLL) attachments as C2-C6 or C2-C7; however, preliminary evidence suggests C2-C5. This study aimed to identify morphological variations in the attachments of the NLL in four species of the family equidae and determine if the variations were species or breed linked. Cadaveric examination evaluated 98 equids; Equusasinus (n = 2), Equus ferus caballus (n = 93), Equus przewalskii (n = 2), and Equus quagga boehmi (n = 1). Twenty breeds of E. f. caballus were included according to breed type-modern horse (n = 81), ancient type (n = 10), primitive (n = 4). Of the 98 equids, observations were divided into three categories according to the NLL attachments: C2-C5, C2-C6, and C2-C7; in category C2-C7, E. f. caballus (n = 3/93), modern horse 0 of 81, ancient 1 of 8, primitive 2 of 4; in category C2-C6, modern horse 2 of 81; in category C2-C5, modern horse 79 of 81, ancient type 7 of 8, primitive 2 of 4. Equus asinus, E. przewalskii, and E. q. boehmi all expressed category C2-C7. In total, 88 of 98 expressed category C2-C5; 2 of 98 category C2-C6; and 8 of 98 category C2-C7. These findings suggest that category C2-C5 provides sufficient evidence to suggest a normal occurrence. The high incidence of an absent NLL on C6 and C7 may be considered a contributing factor in caudal cervical osteoarthritis. Furthermore, category C2-C7 still exists in an ancient and primitive breed closely related to the tarpan, implying the NLL may have been attached from C2 to C7 in prehistoric horse before domestication. This hypothesis is supported by the findings of E. asinus, E. przewalskii, and E. q. boehmi, displaying attachments from C2 to C7., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Hereditary multiple exostoses (HME) is a condition rarely diagnosed in horses, which has not been previously reported in Dutch Warmblood horses. Its presentation resembles that diagnosed in humans, and it is predominantly active during periods of skeletal maturation. This case study reports a link between a granddam with no obvious HME lesions and its first and second generations presenting with HME, albeit with different sires. The severity in affected horses (n = 5) varied from one foreleg to the other with extensive multiple lesions of 123 of 205 bones in a half sibling in the first generation. In the second generation, axial deviations were reported, including similar lesions to those found in the first generation. Rib and limb lesions were the most commonly reported in the first and second generations by age four. However, an extensive examination of the 4-year Dutch Warmblood first generation male revealed lesions from the first cervical vertebra to the first caudal vertebra, inclusive of rib and limb lesions. As all horses with this condition are untreatable, early detection and diagnosis would provide the owner/breeder with options to avoid financial loss and emotional stress., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The Dutch Konik is valued from a genetic conservation perspective and also for its role in preservation of natural landscapes. The primary management objective for the captive breeding of this primitive horse is to maintain its genetic purity, whilst also maintaining the nature reserves on which they graze. Breeding selection has traditionally been based on phenotypic characteristics consistent with the breed description, and the selection of animals for removal from the breeding program is problematic at times due to high uniformity within the breed, particularly in height at the wither, colour (mouse to grey dun) and presence of primitive markings. With the objective of identifying an additional non-invasive selection criterion with potential uniqueness to the Dutch Konik, this study investigates the anatomic parameters of the distal equine limb, with a specific focus on the relative lengths of the individual splint bones. Post-mortem dissections performed on distal limbs of Dutch Konik ( n = 47) and modern domesticated horses ( n = 120) revealed significant differences in relation to the length and symmetry of the 2nd and 4th Metacarpals and Metatarsals. Distal limb characteristics with apparent uniqueness to the Dutch Konik are described which could be an important tool in the selection and preservation of the breed., Competing Interests: The authors declare no conflict of interest.