Faecal K+/Na+ ratio in lame horses and horses with a symmetric motion pattern at trot : a potential biomarker for osteoarthritis?

Abstract: Osteoarthritis (OA) is the most common reason for lameness in horses and is related to chronic pain. The disease is both costly for the horse owner and a welfare issue for the horse and a common cause for horses being culled. It would be helpful both for horse owners and veterinarians to find an early non-invasive biomarker to identify horses with OA. If so, it would be possible to start treatment before severe damage to articular cartilage has occurred. OA is associated with a low-grade inflammation and often affects several joints in the body. The inflammation in the joint influence several biochemical parameters, for example the chondrocytes of the articular cartilage inhibit their synthesis of extracellular matrix protein, downregulates the Na+/K+ pump and glucose transport to the cell. The hypothesis of this study is that an impaired Na+/K+ pump activity in the inflamed cartilage of horses with OA will result in a change in K+/Na+ ratio in faeces. A high ratio could predict OA in horses. The objective of this project was to collect faecal samples from symmetric and lame horses and to analyse the K+/Na+ ratio, to determine whether there is a correlation between the K⁺/Na⁺ ratio and lameness in horses associated with OA. The outcome of the study will define K+/Na+ ratio in faeces as a biomarker for OA or not. In this age-matched study nine symmetric and 27 lame horses were included. Lameness Locator® was used for evaluating locomotion symmetry in healthy horses and 62 horses were measured twice (with four to six weeks in-between). In conjunction with the second measurement a faecal sample was taken. Nine horses were considered symmetric and included in the study. Lame horses were included after a clinical assessment and lameness examination including flexion test and reduced lameness after intra-articular anaesthesia. A faecal sample was taken after the examination. All horse owners responded orally to questions about the horse`s age, training status and supplementary feeding of salt. The concentration of potassium and sodium in the faecal samples were analysed and a ratio for K+/Na+ was calculated from the given values. The mean age of the healthy horses included were 10,2 years and for lame horses 11,1 years. The mean (±SD) K+/Na+ ratio in faeces for the symmetric horses were 8,4 (±8,8) and for the lame horses 8,9 (±24,4). The mean K+/Na+ ratio in faeces for horses (n=10) that received salt supplement daily in the feed was 4,7 (±26,5) and the horses (n=23) that not received any supplementation was 13,2 (±5,0). In conclusion these results show that faecal K+/Na+ ratio is not a suitable biomarker for identifying lameness associated with OA in horses.