10/25/2025
Equine Fluid Therapy
Brian S. Burks, DVM
Diplomate ABVP
Board-Certified in Equine Practice
Horses can lose fluid from the body for a variety of reasons. This is often due to diarrhea, but can be due to other gastrointestinal disorders, blood loss, or any disease that reduces voluntary intake of water. The GIT secretes and absorbs 100 liters (25 gallons) of fluid each day and requires, at minimum, five gallons of water at rest and neutral temperatures. Hot water and exercise can dramatically increase the need for water. There are also insensible losses of fluid from the body by sweat and respiration.
There are four fluid therapy options: voluntary oral intake, enteral, infusion per re**um, and intravenous that can be used to correct dehydration and shock. Their use depends upon the disease and its severity.
Voluntary oral intake is useful in many situations, such as correcting dehydration following exercise, and can replace fluid lost through sweat and respiration. The water may be plain or have added salt. If the horse is given unfamiliar water from a different venue, it may help to cover the taste with gelatin, Gatorade, or alfalfa.
Enteral fluid therapy is used by veterinarians to place water and electrolytes directly into the stomach of the horse via nasogastric intubation. The tube is passed through the nostrils as needed or can be left in place. The intermittent infusion rate for an average adult horse is approximately 10 liters (about 2.5 gallons) every four hours, depending on tolerance and other variables. Such fluid may contain laxatives or substances to absorb toxins in the GIT. It can be used to break down impacted feed stuff in the colon. There are advantages and disadvantages related to technical issues, facilities, and monitoring.
Fluids can be given per re**um, but great care must be taken to prevent rupture of the small colon and re**um. The amount of fluid delivered in this way is less than that of an e***a but can be used when there are diseases that prevent or decrease gastric outflow.
Intravenous fluid therapy is when sterile fluids are given through an IV jugular (usually) vein catheter. Fluid can be administered as replacement or maintenance. Replacement therapy involves giving large volumes of sterile physiologic fluid. Such horses might be affected by enteritis, colic, renal failure, or exertional rhabdomyolysis. The amount of fluid given is based upon clinical presentation and clinical pathology testing.
Maintenance IV fluid therapy is used for horses not allowed to drink or will not drink due to their disease status. It offsets daily losses of water through sweating, breathing, urination, and defecation. Typically, this is about 30 liters of fluid per day (8 gallons) to a full-sized adult horse. From there replacement fluid can be calculated.
To use IV fluids requires knowledge of many factors that affect maintenance needs. Horses that are not eating require less fluid than horses consuming large amounts of dry matter (hay and grain). Diet composition, physical activity, fever, and lactation all affect fluid requirements. Foals have a larger fluid compartment than adult horses, which must be factored into any fluid therapy plan.
Although the most common IV fluids are lactated ringers’ solution and normosol, there other types of fluids such as physiologic saline and half-strength saline. During some disease conditions, every ion must be counted. If the dehydration is so severe that there are fluid and electrolyte shifts from the intracellular to the extracellular space, sudden correction of fluid deficits can be detrimental. Brain cells are highly sensitive to fluid shifts and can suddenly swell during volume replacement, leading to a worsening of neurologic signs. Dehydrated horses are often depressed and will feel better when given fluid, but horses that are so dehydrated that the cells of the central nervous system shrink can develop severe depression and ataxia if too much fluid and sodium are administered. The lack of vascular fluids lowers central venous pressure and thus decreases tissue perfusion so that oxygen is not delivered to the tissues and wastes are not excreted, particularly creatinine. This leads to tissue necrosis and can cause acute renal failure and laminitis, among other things.
Horses with sodium deficits need to have fluid carefully administered. Acute dehydration may require the administration of hypertonic saline solutions to replace the lost sodium, but horses that have had dehydration for several days can have worsening clinical signs during sodium and volume replacement. Other horses will require various electrolyte replacement, including potassium, calcium, and bicarbonate. These replacements must be calculated carefully so as not to cause further harm to the horse.
Fluid is held within the vascular system by oncotic pressure. This ability to maintain the vascular fluid is because of electrolytes, but a large part of what is there is protein in the form of albumin. Horses with diarrhea and other disease states have large losses of electrolytes and protein. Oncotic pressure is therefore treated by replacing electrolytes and protein via crystalloid fluids described above, but also colloid fluids such as plasma obtained from other horses or using synthetic colloids of hydroxyethyl starch, with stay in the vascular system as they do not freely diffuse across the vascular epithelium. Such fluids help to expand the vascular volume and increase central venous pressure, improving circulation and therefore allowing tissue perfusion.
In some cases, delivery of enough fluid to and adult horse can be challenging, but overhydration is possible. The most common consequence is excessive urination and loss of electrolytes. Horses with polyuria should have the fluid rate reduced to conserve costs- sterile IV fluids are expensive.
The goal is always to administer enough fluid as is necessary to make the horse feel better and to allow time for correction of the disease state.
Fox Run Equine Center
(724) 727-3481
www.foxrunequine.com
