Comparison of the effects of intragastric infusions of equal volumes of water, dioctyl sodium sulfosuccinate, and magnesium sulfate on fecal composition and output in clinically normal horses

A Latin square design was used to compare the effects of laxatives and a corresponding volume of water on gastrointestinal tract function in 4 healthy horses. Horses were intragastrically infused with each of the following: dioctyl sodium sulfosuccinate (DSS; 50 mg/kg of body weight); magnesium sulfate (0.5 g/kg-low dosage); magnesium sulfate (1.0 g/kg-high dosage); and an equal volume of water (6 L) given as a control infusion. From 5 to 33 hours after the high dosage of magnesium sulfate, feces were slightly softer than usual in all horses. In 1 horse, DSS caused mild colic, hyperpnea, and diarrhea from 0.3 to 3 hours after administration. After aH laxative treatments and the control infusion, fecal output, fecal water, number of defecations, and fecal water percentage were greater during the first 6 and 12 hours, compared with each subsequent 6-hour period (P < 0.05). The high dosage of magnesium sulfate had greater effect on fecal output and fecal water than did the low dosage and control infusion (P < 0.05). However, this effect preceded arrival of the liquid transit marker, polyethylene glycol, and magnesium at their highest concentrations in feces by 12 to 18 hours. Compared with the control infusion, none of the laxative treatments affected excretion of polyethylene glycol and plastic particulate markers, nor did they increase water consumption. It was concluded that the response to intragastric infusions may involve reflex mechanisms in the gastrointestinal tract and that these responses could be used for treatment of colon impactions. Under conditions of this study, DSS was not a sufficiently effective laxative to outweigh the risk of toxic effects at recommended doses. Although DSS and the low dosage of magnesium sulfate may not provide a greater laxative effect than did an equal volume of water, the high dosage of magnesium sulfate should be more effective.