032 Effects of shoeing on the joints of the lower forelimb and hoof morphology of mature horses

Limited information is available pertaining to potential benefits of barefoot trimming techniques under standard management conditions. Therefore, twelve mature Quarter horses (8-14 y; 450-572 kg) were utilized in a 91-d trial to determine effects of barefoot trimming and shoeing on joints of the forelimb and digital cushion thickness. Prior to the start of the trial, all horses were adapted to a standardized exercise protocol and lameness examinations were performed by a veterinarian; hooves were allowed to grow naturally with minimal farrier interventions. Horses were group housed in adjacent dry lots and provided a commercially available concentrate formulated to meet or exceed 100% NRC requirements with ad libitum access to coastal bermudagrass hay. This study was divided into 2 phases: d 0-42 horses were barefoot trimmed (BF) and d 49-91 horses were shod (SD) on the forehand with standard St. Croix plain lite shoes. Horses were group exercised 3 times per wk on a 132 × 3.7 m linear dirt track. Pedometers were fitted to randomly selected horses to account for steps traveled during exercise. Measurements were obtained every 21 d following exercise and included thermography images (FLIR Systems; Boston, MA) of carpal and metacarpal joints, superficial horn of the frog, and medial and lateral sole of the front digits. Joint circumferences were obtained utilizing a soft tape measure level with the accessory carpal and proximal sesamoid bones, respectively. Digital cushion thickness was also measured ultrasonically through the superficial apex of the frog using a 5.0-MHz convex probe and stand-off pad following previously described methods. Data were analyzed using the PROC MIXED procedure of SAS. Mean circumferences of the carpal and metacarpal joints were greater (P ≤ 0.01) in SD compared to BF. In BF phase, greater (P ≤ 0.01) surface temperatures of the frog, medial, and lateral sole were observed. There was no main effect (P ≥ 0.52) of d or treatment on digital cushion thickness. However, in BF phase horses (1.41 ± 0.13) had greater (P ≤ 0.01) digital cushion thickness at d 42 compared to the equivalent (d 91) in the SD phase (1.26 ± 0.14). These data indicate that a shod fore digit may fail to establish hoof to ground contact that could lead to a limited vascular exchange. This alteration in lower limb and hoof load dispersion may cause an increase in the incidence of lameness over time.