Treatment of Acute Diarrhea. What Really Works ?

Diarrhoea in the adult or neonate can result in marked extracellular fluid deficits. Therefore, the most important treatment for horses with severe diarrhoea is intravenous fluids to help correct these deficits. The rate of fluid administration depends on the severity of dehydration which can be crudely determined by examining the following :

• Dryness of mucous membranes
• Skin Turgor
• Speed of distention of the jugular veins when compressed
• Analysis of the Pack Cell Volume (PCV) or hematocrit (HCT)
• Degree of Azotemia
• Total Protein Levels.

Many clinicians feel that the second most important treatment of diarrhoea is the use of systemic antimicrobials. While there is controversy with this thought process, there may be some merit for this decision when the clinician considers the age of the patient and the etiology of the gastrointestinal disturbance. (Fecal Culture, PCR or Next Generation Sequencing)

Problems with antimicrobials in horses

Antimicrobials can cause adverse gastrointestinal effects in horses because of their activity against commensal bacteria in the intestinal tract. When antibiotics are utilized indiscriminately in patients with diarrhoea are we making a dire situation worse ? Antibiotics that have activity against anaerobes can alter carbohydrate metabolism which can exacerbate a noninfectious cause of diarrhoea. A change in the anerobic bacteria also favors an overgrowth of some bacteria known to be pathogenic such as clostridia. Despite their beneficial properties for treating infections, injudicious antimicrobial use can promote resistance in bacteria in both human and animal populations (1,2). In a recent study conducted by the author demonstrate empirically that widespread use of macrolides and rifampin at horse farms in foals with subclinical R. equi infections results in propagation of resistance to macrolides in R. equi but also resistance in other fecal bacteria to many other antimicrobials. This is what was unexpected that the use of one class of antimicrobial can actually result in the resistance of a different class of antimicrobial.

Age of the horse

In a study at the University of Pennsylvania, Veterinary School titled Bacteremia in equine neonatal diarrhea : a retrospective study (1990-2007), the authors concluded that bacteremia is common in foals (< 30 days of age that were admitted to a tertiary clinic) with diarrhoea. 50% of the foals admitted to the university with diarrhoea were bacteremia with 57% noted to have a gram-negative organism and 43% noted to have a gram-positive organism. Decisions regarding antimicrobial selection should be made with these differences in mind. The author currently treats all diarrheic foals that present to the hospital with broad spectrum antimicrobials. The risk of bacteremia in young foals with a compromised mucosal barrier that later develop septic physitis or synovitis is just too high for a clinician to debate about starting antimicrobials.

Salmonellosis

Although antibiotic administration is frequently avoided to treat adult horses with salmonellosis, there may be exceptions for which antibiotic us is indicated (Prolonged Pyrexia and /or Critical Leukopenia). Ina study by the author looking at duration of salmonella shedding in adult horses it was noted that horses that receive oral antimicrobials tend to shed for longer median duration than horses receiving either parenteral or none. It is possible that the antibiotic administration decreases the competitive balance in the intestine and allows Salmonella spp. to proliferate and shed. [...]