The foal showed and IVVP diameter relatively smaller than adults, whereas the young adult specimen (2.5 years) showed IVVP diameters similar to the observed in the mature adult.
The abundant drainage of the meninges toward the IVVP increases the calibre of these veins contributing to the cushioning and protection of the spine (Gomez Jaramillo & Freeman).
Cranial (T1-T2) and caudal (T16-T18) thoracic segments presented a larger IVVP diameter.
Lumbar IVVP in the foal was poorly developed, where the diameter of these veins was 50 % minor than adults.
The IVVP in horses has a similar morphology to that observed in other mammals.