The effect of plain, eggbar and 6 degrees-wedge shoes on the distribution of pressure under the hoof of horses at the walk.

Abstract: To quantify the effect of plain, wedged and eggbar shoes on the distribution of pressure under the hoof of horses at the walk, at selected areas of interest (AOI), to find scientific evidence for the perceived efficacy of these shoes in the treatment of palmar heel pain. Methods: Six clinically sound adult Warmblood mares weighing 551 (SD 25) kg were shod (forelegs) with either plain, eggbar or 6 degrees-wedge shoes using a latin-square experimental design. All horses were shod by the same farrier, and each balanced and aligned for its individual conformation. Data were collected on three walking strides for each foreleg using a 550 x 405-mm pressure plate to quantify the distribution of pressure under each type of shoe at five AOI. Results: Landing of the hoof with all three shoes was predominantly from lateral to medial (range 7-15 msec). Irrespective of the type of shoe, the greatest pressure was found in the lateral and medial toe (lateral 39.7 (SE 0.6) N/cm2 and medial 35.0 (SE 0.5) N/cm2) and the point of the toe (33.3 (SE 0.5) N/cm2). The lowest peak pressure was in the heel (lateral 25.9 (SE 0.5) N/cm2 and medial 21.1 (SE 0.4) N/cm2; p<0.05). Eggbar and wedge shoes increased total stance time (938 (SE 8) msec and 952 (SE 6) msec, respectively) compared with plain shoes (898 (SE 14) msec) (p<0.05). The wedge shoe reduced breakover compared with the plain and eggbar shoes (13.8% vs 15.8% and 14.5%, respectively; p<0.05). The eggbar shoe had lower total shoe peak pressure (29.5 (SE 0.7) N/cm2) than plain (31.8 (SE 0.5) N/cm2) and wedge (30.9 (SE 0.6) N/cm2) shoes. Conclusions: Both the eggbar and 6 degrees-wedge shoe offer advantages for palmar heel pain. In comparison to the plain shoe, the eggbar shoe had less peak pressure at the heel AOI, and across the entire shoe, due to the greater bearing surface and the effect of the longer heel. The 6 degrees-wedge shoe had greater loading on the lateral heel AOI, but promoted earlier breakover at the toe. Both shoes offer advantages for the horse with palmar heel pain, though choice of shoe will depend on clear identification of the causative factors, to provide therapeutic shoeing that maximises the individual horse's response.