Preliminary Investigations Into Photogrammetric Measurement of Hoof Shape

Introduction Advances in close-range photogrammetry offer an option for high accuracy measurements of the equine hoof. Automatic camera calibration using coded targets, image matching and triangulation enables 3D model reconstruction from photographs. This study aimed to identify an accurate photogrammetric method to measure proximal hoof circumference (PHC). PHC is currently measured by hand and shown to change in racehorses during training. Methods A cadaver hoof was measured by hand, photographed, and laser scanned for method comparison. Then, the left front hooves of two adult horses were photographed under two treatments (exercise and control). Exercise involved 5 minutes brisk trot counter-clockwise on a lunge-line. During both experiments a Canon 40D camera (28–135 mm lens; F5 aperture; 1/60 sec shutter speed) was used. Hooves were marked with permanent marker and coded targets placed on the ground around the hoof for automatic point identification. Photos were taken from 10–16 different locations around the hoof. A paired t-test was used for comparisons and significance set at P<0.05. Results Photogrammetry produced a 3D model of the cadaver hoof which was considered good (accuracy of 0.25 pixel RMS). Points on the hoof were manually identified and model creation took 1.5 hours. PHC measurements from photogrammetry differed from the laser scan by 1.25 mm and from hand measurements by 1.73 mm. PHC decreased following exercise (0.8 mm; p = 0.25). Conclusions Close-range photogrammetry could be viable for highly accurate and quick measurements of hoof shape. Advantages include; ease of data acquisition, flexibility, low cost, evaluation of the loaded hoof, and high geometric accuracy. To measure only PHC eight images or less could be used. Additional research is required to determine repeatability and accuracy. Ethical Animal Research Procedures were approved by the University of Melbourne's Animal Welfare and Ethics Committee. Sources of funding: University of Melbourne. Competing interests: none.