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A MAJOR goal of prophylactic antimicrobial administration is to prevent incisional infection, an important cause of morbidity after equine colic surgery. The inclusion criteria used in the study by Durward-Akhurst and others (2012), which is summarised on p 287 of this issue of Veterinary Record, created two comparable sets of colic cases at two referral hospitals to study the timing of antimicrobial administration to prevent this complication. The study found no difference between 72 hours and 120 hours of prophylactic antimicrobial administration in preventing incisional infections and, therefore, the shorter period should be preferable; postoperative antimicrobial use for long durations in horses could promote emergence of resistant organisms (Morley and others 2005) and induce diarrhoea ( Cohen and Woods 1999 ).
The critical question is whether or not we should give antimicrobial agents to horses at all after colic surgery is completed. One option is to follow the evidence-based practice for human clean-contaminated surgery, in which antimicrobial prophylaxis is not recommended after wound closure (Bratzler and others 2013). In the two groups of horses described by Durward-Akhurst and others (2012) almost 17 per cent had exploratory surgery only. Such procedures should be regarded as clean and, therefore, should not qualify for antimicrobial prophylaxis according to the strictest guidelines ( Brown 1999 ) and experience with other large animal procedures ( Klein and Firth 1988 , Borg and Carmalt 2013 ). However, acute colic seems to increase the risk of incisional complications compared with elective abdominal surgery (Wilson and others 1995).
Although preoperative findings might not predict the need for a clean-contaminated procedure (such as enterotomy or enterectomy), and since most colic surgeries are clean-contaminated (Durward-Akhurst and others 2012), all candidates for colic surgery should receive preoperative antimicrobials. If the surgery does qualify as clean, then antimicrobials could be discontinued after surgery. Preoperative use only has been validated in human colorectal surgery (Baum and others 1981) and for rumenotomy in steers (Haven and others 1992). Longer periods of antimicrobial administration could be indicated for horses with a pre-existing septic process, such as uterine tear or other forms of peritonitis.
The most common reasons for reinstituting antimicrobial therapy or for changing antimicrobial class after colic surgery are fever and signs of incisional infection (Dallap Schaer and others...