The effects of wooden blocks on load distribution in fore- and hind limb claws of dairy cows.

Introduction
Application of blocks to treat claw horn lesions in dairy cows is a procedure commonly carried out by farmers, hoof trimmers, and veterinarians. Although the positive effects of this treatment have long been known (Nuss and Tiefenthaler, 2000, Wehrle et al., 2000), scientific studies have been done only recently (Thomas et al. 2015). Little is known about the effect of a wooden block on the limb it is attached to and the load distribution changes in the contralateral limb. Therefore, the aim of our study was to determine whether changes in weight distribution occur in the fore- and hind limbs of dairy cows after application of a wooden block. 

Materials and Methods
A custom-made wooden block, 3 cm thick, was temporarily attached with duck tape to the lateral claw of the left forelimb in 30 dairy cows for the measurements. The load, consisting of vertical ground reaction force, sole imprint area, and mean and maximum pressure were measured simultaneously in both forelimbs. Data were acquired using a platform containing a force plate, which was connected to a pressure plate, an interface box, and a PC. The block was then removed and attached to the medial claw of the left hind limb, and the same variables were measured in the hind limbs. 

Results
With a wooden block on the lateral claw of the left forelimb, there was a tendency for the cow to transfer weight to the right forelimb, but the mean ground reaction forces exerted on the limbs and claws measured before and after block application did not differ significantly. As expected, the load of the left forelimb was exclusively transferred to the claw to which the block was attached to. Similarly, with a wooden block on the medial claw of the left hind limb, there was a tendency for the cow to transfer the load to the right hind limb. The pressures, but not the mean ground reaction forces exerted on the limbs and claws measured before and after block application did differ significantly. However, the vertical ground reaction forces and pressures transferred to the bulbar zone of the lateral claw of the hind limb contralateral to the block increased significantly. Also, there were changes in load distribution in the lateral and medial claws of the contralateral hind limb. 

Conclusions
A 3-cm wooden block fulfilled expectations in that it offloaded the partner claw. Within the 2-second measuring period, there was no significant transfer of load towards the contralateral limb. When we analysed the sole and bulbar zones of the claws separately, there were significant changes in the hind limb contralateral to the block. There, the vertical ground reaction forces and pressures transferred to the bulbar zone increased significantly. These findings indicate that a wooden block should be removed as soon as the claw lesion in the partner claw has healed to avoid increased loading of the claw with the wooden block and to avoid increased loading of the bulbar area of the contralateral lateral claw in the hind limbs.