The Disappearing Lamellae: Implications of New Findings in the Family Equidae Suggest the Loss of Nuchal Ligament Lamellae on C6 and C7 Occurred After Domestication.

This research investigates the variations in the attachments of the equine nuchal ligament lamellae (NLL) in different horse species and breeds, with an interesting discovery that the NLL loss on the C6 and C7 parts may have happened after domestication.

Motivation and Aim of the Study

• The focus of this study stems largely from conflicting data about which segments of the cervical spine the equine nuchal ligament lamellae (NLL) are attached to. There are varying claims that the NLL either attaches from C2 to C6, C2 to C7, or as recent preliminary evidence suggests, from C2 to C5. The lack of consensus prompted this research to confirm these attachments and investigate the potential relationships with species or specific breeds.

Research Methodology

• Cadaveric examination was the primary method used in the research, with 98 carcasses from four different species of the equidae family (horses and relatives) examined to explore the morphological differences in the NLL’s attachment sites. This included two donkeys (Equus asinus), 93 domestic horses (Equus ferus caballus) split into 20 different breeds, two Przewalski’s horses (Equus przewalskii), and one Grant’s Zebra (Equus quagga boehmi).

Findings of the Study

• The results revealed three distinct categories for NLL attachments: C2-C5, C2-C6, and C2-C7, across the subjects. Examination of E.f.caballus showed that most modern, primitive, and ancient type horses fell in the C2-C5 category. Conversely, the E.asinus, E.przewalskii, and E.q.boehmi specimens all showed NLL attachment from C2 to C7, which is categorised under C2-C7.
• In total, 88 of the 98 subjects expressed the C2-C5 category, 2 fell in the C2-C6 category, and 8 corresponded to the C2-C7 category. This notably high incidence of the C2-C5 category suggests that this is the most common attachment point for the NLL.

Implications of the Findings

• From these results, the researchers posited that the high prevalence of an “absent” NLL on C6 and C7 could contribute to the development of caudal cervical osteoarthritis, a degenerative joint condition often found in horses. They further hypothesised that the more seldomly observed C2-C7 attachment might have been usual in prehistoric, undomesticated horses, considering its presence in more ancient and primitive breeds related to the tarpan horse, and the other undomesticated equidae species.