The Occurrence of a Congenital Malformation in the Sixth and Seventh Cervical Vertebrae Predominantly Observed in Thoroughbred Horses

During the dissection and skeletal examination of 123 horses, it was observed that a significant number had a gross skeletal congenital malformation of the sixth and seventh cervical vertebrae. In the sixth cervical vertebra (C6), either a unilateral or bilateral absence of the caudal ventral tubercle (CVT) was noted. In the presence of the C6 malformation, the seventh cervical vertebra (C7) presented either as normal or with a unilateral or bilateral transposition of the CVT from C6 onto the ventral surface of C7 with an arterial foramen. This transposition onto C7 was noted to be present on the corresponding side as the absent CVT on C6. Of the 123 horses examined, the congenital malformation of C6 was noted in 19 of 50 Thoroughbred horses; three of three Thoroughbred derivative horses; one of 15 nondescript bred horses; and none of 55 purpose bred horses of mixed breeds. In total, 23 horses expressed a C6 congenital malformation of which 22 were Thoroughbreds or Thoroughbred derivatives. Of these 22 Thoroughbred and Thoroughbred derivative horses, 11 of 22 expressed either a unilateral or bilateral transposition of the CVT from C6 onto the ventral surface of C7 with an arterial foramen on the corresponding side. This malformation could have functional and clinical ramifications in the postural and locomotive properties of the equine neck and cervicothoracic junction as reported in other species.