BACKGROUND In dressage, the head and neck position has become an issue of concern as certain extreme positions may imply a welfare risk for the horse. In man, extension and flexion of the cervical spine cause a decrease and increase in intervertebral foramina dimensions, respectively. However, in horses, the influence of flexion and extension on foramina dimensions and its possible interference with peripheral nerve functioning remains unknown. OBJECTIVE To determine the effect of ex vivo flexion and extension on intervertebral foramina dimensions in the equine cervical spine. METHODS Computed tomography was performed on 6 cadaver cervical spines from adult Warmblood horses subjected to euthanasia for reasons unrelated to cervical spine abnormalities, in a neutral position, in 20 and 40° extension, and in 20 and 40° flexion. Multiplanar reconstructions were made to obtain transverse images perpendicular to the long axis of each pair of intervertebral foramina from C2-T1. Intervertebral foramina dimensions were measured in the 5 positions. RESULTS Compared to the neutral position, 40° extension caused a decrease in foramina dimensions at segments C4-C5, C5-C6, C6-C7 (P < 0.001) and C7-T1 (P < 0.002); 20° extension caused a decrease in foramina dimensions at segments C5-C6 (P < 0.02), C6-C7 (P < 0.001) and C7-T1 (P < 0.01); 20° flexion caused an increase in foramen length at segment C6-C7 (P < 0.01). CONCLUSIONS Ex vivo extension of the cervical spine causes a decrease in intervertebral foramina dimensions at segments C4-T1, similar to that found in man. CONCLUSIONS In vivo extension of the cervical spine could possibly interfere with peripheral nerve functioning at segments C4-T1. This effect may be even more profound in patients with a reduced intervertebral foramina space, for example in the presence of facet joint arthrosis.