Summary The medical records of 192 horses with septic arthritis/tenosynovitis 1979–1989 were reviewed. Forty‐three horses developed infection after an intra‐articular injection, 46 following a penetrating wound, 25 following surgery, 66 were foals less than 6 months old, and 12 were adult horses without a known aetiology. Haematogenous infection of a joint occurs in adult horses and should be considered as a differential diagnosis in horses with an acute onset of severe lameness. The aetiology of the infection had a significant effect on the type of bacteria identified by culture. Staphylococcus was cultured from most of the horses that developed infection following a joint injection or surgery, 69% of the horses from which an organism was identified. Horses that developed infection secondary to a penetrating wound frequently provided cultures of more than one organism; Enterobacteriaceae and anaerobes were more frequently isolated in this group. The most common organisms isolated from foals were Enterobacteriaceae; E. coli was identified in more than 27% of the foals. The hock was the most frequently involved joint. Multiple treatments were used over the 10‐year period of study. Survival rates were lowest in foals; only 45% survived to be released from the hospital. Survival was greater in adult horses; 85% of the horses that were treated were released from the hospital. Survival was significantly greater in horses with septic tenosynovitis; all 14 of the horses that were treated survived. Survival was not significantly affected by the joint involved or by the type of bacteria cultured from the synovial fluid. Follow‐up racing data were obtained for all horses of racing age that were released from the hospital; 56.5% of these horses returned to racing and over 45% of these horses were able to make at least 5 starts. We suggest that if the infection can be eliminated before irreversible damage to the articular cartilage occurs, horses can return to athletic function.

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Summary Bacterial culture and susceptibility results were analysed from 233 horses with septic arthritis/tenosynovitis or osteomyelitis that developed after fracture repair. Antibiotics were deemed highly effective, effective or ineffective if ≤85%, 70–84.9% or <70% of the isolates were susceptible respectively. In total, 424 bacterial types were isolated; 386 were aerobic or facultative and 38 were anaerobic. Enterobacteriaceae (28.8%) were the most common bacterial group isolated, followed by non‐beta‐haemolytic streptococci (13.0%), coagulase‐positive staphylococci (11.8%), beta‐haemolytic streptococci (9.4%), and coagulase‐negative staphylococci (73%). The remainder of the organisms were other Gram‐negative (15.8%), other Gram‐positive (2.3%) and miscellaneous (2.6%) bacteria. Penicillin and ampicillin were highly effective against beta‐haemolytic streptococci, but were ineffective against other bacteria. Ampicillin was no more effective than penicillin against most bacteria. Amikacin was the most effective antibiotic against the wide range of bacteria isolated in this study. Amikacin was highly effective against coagulase‐positive staphylococci, Enterobacteriaceae and Pseudomonas and was effective against coagulase‐negative staphylococci and Actinobacillus. Gentamycin was not highly effective against any bacterial group; but was effective against coagulase‐positive and negative staphylococci, Pseudomonas, Salmonella and Actinobacillus. Kanamycin was ineffective against all bacteria with the exception of Actinobacillus. Cephalothin was highly effective against beta‐haemolytic streptococci, coagulase‐positive staphylococci and Actinobacillus and was effective against coagulase‐negative staphylococci. Cephalothin is a very useful antibiotic for Gram‐positive organisms, especially staphylococci, which are an important cause of iatrogenic infections. Trimethroprim‐sulphonamides were highly effective against Actinobacillus and were effective against coagulase‐positive staphylococci, beta‐haemolytic streptococci, non‐beta‐haemolytic streptococci and Rhodococcus equi. Due to the narrow spectrum of activity of trimethoprim‐sulphonamides against the common pathogenic organisms, these drugs should be used only after culture and susceptibility results are known. Erythromycin was highly effective against coagulase‐positive staphylococci, beta‐haemolytic streptococci and Rhodococcus equi and was effective against coagulase‐negative staphylococci. Chloramphenicol was effective against a wide range of organisms, but it cannot be recommended because of the human health hazard associated with handling this drug. Other less commonly used antibiotics were effective against some types of bacteria. The combination of a cephalosporin and amikacin provides the best coverage against the bacteria isolated in this study. These are the antibiotics that should be considered when treating horses with musculoskeletal infection before culture and susceptibility results are known. However, these drugs are not recommended for prophylaxis in ...