Novel approach for modelling force and pressure distribution inside bovine claws and on different surfaces

Introduction 
The sustainability of the dairy industry is threatened by growing problems of claw disorders. One of the main risk factors is uneven weight distribution on hard and rough surfaces causing a compression of the corium between the claw bone and the sole horn (Lischer et al., 2002). Problems in weight distribution between and within claws are mainly caused by imbalance between claw horn growth and wear due to quality of walking surface in cattle barns (Telezhenko et al., 2008, 2009). What is really important for evaluation of the possible floor effects on claw health is to determine weight and pressure distribution directly at the corium along the weight bearing surface. Yet, all studies to date examined claw pressure distribution between outer edge of claw sole and floor surface (van der Tol et al., 2004; Carvalho et al., 2005; Oehme et al., 2018), which makes extrapolation of the real pressure directed to the vulnerable inner claw structures more difficult. This study represent a novel approach to study force and pressure distribution inside the sole of bovine claw for better understanding of biomechanical effects of different surfaces and claw shape. 

Materials and Methods
Three hind limbs of adult dairy cows from a slaughterhouse (2 Holsteins and one Swedish Red) separated below the tarsometatarsal joint were used. The claws were untrimmed but without significant overgrowth (toe length 79.6 ± 0.3 mm, mean ± SE). The specimens were tested in a special designed rig with stepless controlled application of both vertical load and stretching of deep and superficial flexor tendons, which emulates the natural load situation. The biomechanical measurements were performed with the I-Scan system (Tekscan Inc., Boston, MA) using pressure sensors (5101 CMP, Tekscan Inc.), which were set up as an ultrathin (0.10 mm) flexible printed circuit with a density of 15.5 sensing elements per cm². The sensors were inserted inside the sole over the whole weight bearing surface in the lateral and medial claw at the edge of the corium-claw horn junction, respectively. The thickness of the sole horn between sensor and the corium was 1 mm and average thickness of the claw horn between the sensor and ground surface was 7.2 ±0.4 mm (mean ± SE). The claw horn surfaces in contact with pressure sensor were made flat and a thin double adhesive tape was used to assemble claw and the sensor together. The exerted vertical force was on average 1400 N, and deep and superficial flexor tendons were pooled with a force of 1200 N, which was within the range of 0.74–1.06 of the ratio between force excreted on of the tendons and vertical load measured in horses (Takahashi et al., 2010). Three measurements were performed per foot, where each measurement included 100 frames.  […]