Equine fluid therapy

- Introduction

Fluid therapy is a key component in treatment and supportive care of horses with a variety of conditions, especially those with critical illness. fluids are drugs and, as such, have the potential for both life-saving benefits and serious, possibly life –threating, adverse effects in order to better align their utilization with their characterization as drugs. Water balance in the horse physiologic response to feeding and water loss or deprivation, and methods used to correct dehydration. Under normal environmental conditions horses tend to consume around 50 ml/kg/day of free water. This represents around 25 liters a day for a 500 kg animal. This value varies with environmental temperature and humidity, physical exercise, and diet. Water is an important component of the fermentation process in the large intestine and horses on hay diets will consume more water than those on meal-based diets. The intestinal tract receives fluid in the form of saliva, and gastric, pancreatic and biliary secretions. This may be around 125 - 150 liters daily in a 500 kg animal. This includes 30 - 50litres of pancreatic fluid, 12 - 25 liters per day of biliary fluid, around 50 liters per day of saliva, and a variable amount of gastric secretions.The process of hind gut digestion is dependent on large water and electrolyte fluxes in the caecum and large colon. Hind gut digestion in equids is superior to rumen digestion for dealing with high fiber plant material, provided that food intake and the rate of digesta passage are not limited through feed availability.These large intestinal fluid fluxes are maximized by meal feeding. Episodic feeding promotes movement of fluid and sodium into the intestinal tract causing a transient reduction (10-13%) in plasma volume leading to renin and angiotensin II release. Aldosterone release follows to promote post-prandial retention of sodium at renal, colonic, and other target epithelia, in exchange for potassium or hydrogen ions. Aldosterone causes a reduction in urine volume and decrease in plasma protein.