Summary Reasons for performing study: Wound healing proceeds faster in ponies than in horses and complications during healing, such as wound infection, occur less frequently in ponies. Earlier studies suggested that this difference might be related to differences in the initial post traumatic inflammatory response. Hypothesis: That polymorphonuclear leucocyte (PMN) function and profiles of humoral factors in local inflammatory processes are different in horses and ponies. Methods: PMNs were isolated from venous blood of horses and ponies. Chemotaxis and reactive oxygen species (ROS) production was determined. Tissue cages were implanted in limbs and necks of horses and ponies and injected with carrageenan and, 3 weeks later, with LPS. In sequential samples of inflammatory exudate, the numbers of macrophages and PMNs and the production of PGE2, TNFα, IL‐1, IL‐6 and chemoattractants were determined. Results: In vitro ROS production of PMNs was significantly higher in ponies than in horses, whereas in vitro PMN chemotaxis was significantly lower in ponies. In the tissue cages for both stimuli, the production of IL‐1 and chemoattractants was significantly higher in ponies than in horses and remained so towards the end of the observation period in ponies. Conclusions: This study demonstrated a higher production of various inflammatory mediators by pony leucocytes. Despite the lower in vitro chemotaxis of pony PMNs, this higher in vivo production resulted in a stronger initial inflammatory response in ponies, as has been reported in studies on wound healing, through the attraction of leucocytes and triggering of the production of other cytokines. A stronger initial inflammation may promote healing by more rapid elemination of contaminants and earlier transition to repair. Potential relevance: Modulation of the initial inflammatory response might therefore be a valid option for therapeutic intervention in cases of problematic wound healing. Further, the intraspecies differences in leucocyte function may have an impact on many fields in equine medicine.

Summary Equine acute abdominal disease is often associated with shock. Important aspects in the onset of this complication include hypovolaemia, the translocation of endotoxins from the gut and the subsequent activation of the cytokine network. The clinical efficacy of high volume continuous venovenous haemofiltration (HV‐CVVH) and the clearance of cytokines were therefore investigated in an equine endotoxaemic model. Ten male Shetland ponies received a slow infusion of LPS (2 μg/kg bwt) under general anaesthesia. The treatment group (n = 5) received HV‐CVVH (2 ml/kg bwt/min) using a 75 kD polymethylmethacrylate (PMMA filter). Haemodynamic, blood variable and cytokine (TNF, IL‐1 and IL‐6) measurements were performed every 30 min for a 6 h period. The ponies showed a typical reaction in mean pulmonary arterial pressure, blood chemical and haematological markers after LPS challenge. No significant differences were found between the treatment group and the control group. Only a slight increase in cardiac index and no marked decrease in mean arterial pressure were seen. A clear cytokine response was found in all ponies, though substantially different in magnitude between individuals. The clearance of cytokines from the blood increased in time, but did not lead to significant decrease in serum levels. In this study, HV‐CVVH with a PMMA filter did not prove to have a significant beneficial effect on the course of experimental endotoxaemia in horses. However, in a more severe model, better efficacy might be obtained. Testing additional filters might lead to a more suitable therapy for horses.