Polysynovitis after Oligofructose Overload in Dairy Cattle

SummaryAcute bovine laminitis is a systemic disease with local manifestations primarily affecting the claws. However, distension of the tarsocrural joints has been observed after experimental oligofructose overload in dairy heifers as a part of the complex interpreted as acute, clinical laminitis. Therefore, the aim of the present study was to study bovine synovial joints and tendon sheaths after oligofructose overload. Ten dairy heifers received oral oligofructose overload (17 g/kg body weight); four were killed 24 h after overload and six after 72 h. Six control heifers received tap water and were killed after 72 or 96 h. Clinical examination included locomotion scoring and palpation of the tarsocrural joints. Ruminal fluid and blood was collected for measurements of pH and hydration status. Total protein concentrations and white blood cell (WBC) counts were determined in synovial fluid collected from tarsocrural joints after death. Synovial joints and tendon sheaths were examined and synovial membranes were studied microscopically. Swabs taken from the synovial cavities were subject to bacteriological culture. Heifers with oligofructose overload developed signs of ruminal and systemic acidosis. Lameness was observed in three of ten heifers 24 h after overload and in all remaining heifers after 72 h. Distension of tarsocrural joints was observed from 18 h after overload and peaked at 30 h when all examined joints were moderately or severely distended. The synovial fluid was turbid and protein content and WBC counts were increased at both 24 and 72 h compared with controls. Bacterial culture was negative. Synovial membranes 24 and 72 h after overload had a fibrinous and neutrophil inflammatory reaction that regressed in severity between 24 and 72 h after overload. Heifers subjected to oligofructose overload therefore developed generalized sterile neutrophilic polysynovitis. Focus on this aspect of bovine laminitis may shed new light on the pathogenesis of this complex disease.