Existing recommendations suggest the condition should be treated with antibiotics regardless of its cause, but the evidence indicates that treatment with antibiotics is unlikely to improve pregnancy rates in mares and may even be detrimental to fertility. As such, clinicians should use antibiotic intervention judiciously, apply additional diagnostics to identify the cause of endometritis and avoid antibiotics altogether in mares with no history or signs of the condition.
The data was reported in January’s Knowledge Summary entitled “The use of antibiotics in broodmares with post-service endometritis”, which sought to uncover whether, based on current evidence, antibiotic treatment is superior to other routine therapies at improving pregnancy rates.
Collectively, the evidence provided by the seven relevant studies identified did not support the existing assumption that antibiotics delivered into the uterus post-service increase the likelihood of pregnancy. But the evidence does demonstrate that some treatment with routine therapies – with or without antibiotics – is better than no treatment at all in mares with endometritis.
Considering there are a number of possible non-antimicrobial therapies for endometritis (including lavages, mucolytics, immune modulation treatments and ecbolic agents), establishing whether intrauterine antibiotic intervention is more, less or as effective is important in preventing the unnecessary use of antibiotics. It is worth acknowledging therefore that there is no evidence in the studies that intrauterine antibiotics increase pregnancy rates when compared to other therapies. In fact, the current data shows that, when used individually, ecbolic agents and antibiotics have similar effectiveness. Notably however, when combined, the effects of antibiotics and ecbolic agents appear to synergise and provide higher pregnancy rates compared to using them as standalone treatments. Dual therapies are consistently shown by the evidence to be more effective than individual treatments. Interventions with lavage and oxytocin; antibiotics and oxytocin; and lavage, oxytocin and antibiotics all demonstrated pregnancy rates of between 45 and 62 percent.
The fact that there is little difference between the pregnancy rates produced by various combinations has increased significance when taking into account why intrauterine antibiotics are currently – unnecessarily – recommended for all cases of endometritis in mares. It is thought that intrauterine antibiotics enhance fluid removal by causing cervical dilation, but the evidence demonstrates that other, non-antimicrobial intrauterine therapies encourage the same process, hence restricting the need for antibiotics to their effect on pathogens.
Diagnosis, culture and sensitivity
Endometritis can be notoriously difficult to diagnose, made more challenging by the lack of a clear definition of the condition. It is clear from the evidence that additional diagnostic methods such as culture and cytology of endometrial samples should be employed to establish whether individual cases of endometritis are bacterial in nature.
Furthermore, isolating the bacteria involved (assuming the cause is pathogenic) is important to ensure an appropriate sensitive antimicrobial is used, and also for minimising the use of widely resisted or restricted antibiotics.
In one study, all isolates were sensitive to gentamicin and ceftriaxone (although it is worth noting that types of bacteria are likely to vary geographically). Streptomycin was heavily resisted – in the case of E. coli, by 100 percent – while penicillin showed both moderate resistance and sensitivity. As such, the currently available evidence indicates the need for further research in the diagnosis of post-service endometritis and the pathogens involved.