INDUCED DIARRHEA IN HORSES PART-2 - RESPONSE TO ADMINISTRATION OF AN ORAL REHYDRATION SOLUTION

Hydration status, electrolyte balance and acid-base balance were studi ed in four adult standardbred geldings with castor oil-induced diarrho ea. The horses received an oral rehydration solution (ORS) at a point when signs consistent with mild decreases in effective circulating flu id volume were first detected. within 1.5 h of ORS administration, all horses exhibited a significant metabolic acidosis. At this time, mean values for venous blood pH, [HCO3], and standard base excess were 7.2 64+/-0.011, 17.7+/-0.3 mmol L-1, and -8.2+/-0.4 mmol L-1, respectively . Throughout the duration of the study, plasma volume did not change s ignificantly, despite a decreasing trend, which tended to recover towa rds normal values 8 h after administration of the ORS. Signs of abdomi nal discomfort were observed in all horses following the last of three doses of ORS (8-10 L) administered at 30 min intervals. Faecal fluid sodium concentration increased significantly with diarrhoea, and reach ed values fourfold those in normal horses, while faecal dry matter sod ium concentration increased exponentially following the onset of clini cal signs. Despite this increase in sodium concentration, faecal fluid remained hypotonic at all stages. Our findings suggest that, while OR S can help restore systemic fluid balance, several factors influence t heir effectiveness. Two likely factors identified in this study were t he ionic composition of the ORS as well as the rate of administration. We concluded that the electrolyte composition of current ORS may not be ideal to treat diarrhoea in horses and that administration of 8-10 L, of ORS every 30 min via nasogastric tube may result in too rapid sm all intestinal transit to allow sufficient time for absorption.