Pressure mat analysis for detecting and quantifying lameness in pigs

Lameness is a common problem in modern swine industry, affecting both animal welfare and economic profit for the farmer. Animal welfare may be affected due to pain and the resulting reduced mobility. A lame pig may not be able to reach feeding and drinking facilities and may have a higher risk to be overrun by penmates.The economic impact of lameness is caused by lower productivity and higher costs of treatment or early culling of affected animals . The aforementioned welfare and economic issues can be minimized if veterinarians provide evidence-based advice on interventions to treat and prevent lameness. These interventions need to be assessed using objective, sensitive and repeatable methods to quantify lameness. Traditionally, visual assessment of gait is used most often to quantify lameness. Although this method is fast and inexpensive, it has several drawbacks. Visual assessment may suffer from inherent subjectivity, is affected by observer bias and has limited intra- and inter-rater agreement, especially in untrained observers and in mild lameness. Pressure mats may provide a solution to this problem. They consist of many pressure sensors in a dense grid, which collect data on both loading and timing of gait. In this thesis, the use of pressure mats to detect and quantify lameness in pigs has been validated. The first part of the thesis explored influencing factors on pressure mat paramaters in healthy, growing pigs. Parameters of individual limbs were influenced by several factors such as velocity, measurement session and front-or hindlimb. Therefore, asymmetry-indices, comparing loading of limbs within one run, were used to minimize the effects of variations between runs. Asymmetry-indices of healthy pigs were repeatable, remained stable over time and were not influenced by velocity and front-or hindlimb. In the second part of the thesis, asymmetry-indices of lame and sound pigs were compared to each other. Limb loading of lame pigs was more asymmetric compared to sound pigs and correlated well with the sverity of the lameness. Also, the effect of a strong analgesic could be detected by the pressure mat, but not by visual inspection. Pressure mat analysis was therefor considered a sensitive and objective method to quantify lameness. In the third part of the thesis, with pressure mat analysis validated as a useful method, it was used to determine the effect of a non-steroidal anti-inflammatory drug (NSAID) on experimentally induced osteoarthritis. Lameness was assessed on several timepoints. Only on the last timepoint, at day 56 post-induction of osteoarthritis, an effect of NSAID treatment was seen. In conclusion, pressure mat analysis of lameness in pigs provided a useful method to detect and quantify lameness in pigs under laboratory conditions.