Is Hot Weather Making My Horse's Legs Stock Up?

Q. Recently, we have been experiencing some very hot weather, and I noticed that my horse’s legs are stocking up. This has not happened before. Could this be related to the heat, and is there anything I can do nutritionally that might help?

A. “Stocking up” is swelling in the lower limbs caused by pooling of lymph, a fluid containing infection-fighting white blood cells that circulates through the lymphatic system. Stocking up is typically temporary and often occurs due to reduced activity, which impairs circulation. It is commonly seen in horses that live outside that are brought in for a time and, therefore, do not move as much as normal. Sometimes, though, it develops in other scenarios.

Step One: Check for Injury or Illness

Any time limbs swell, it’s important to check for heat and pain to determine whether the cause might be an injury. Also, take your horse’s temperature; if it’s elevated, he could have an infection.

Stocking up should not be painful to the horse or result in a fever or reduced appetite. These signs would suggest something more serious is at play. If in doubt, always contact your veterinarian; some conditions, such as cellulitis, present like stocking up but are more severe and require medical treatment.

Lymphatic System Basics

If you’ve determined stocking up isn’t due to injury, illness, or other health issues, you’re likely dealing with pooled lymph.

The lymphatic system is part of the circulatory system and follows blood flow around the body. Oxygen- and nutrient-rich blood travel away from the heart and to the horse’s extremities, where very small arteries (arterioles) and tiny capillaries carry it. Oxygen and nutrients leak from the capillaries and into the surrounding tissues, which use them for metabolism and other cellular functions. The deoxygenated blood then travels back in vessels, and the lymphatic system transports any waste products or unused nutrients to the lymph nodes (where they’re filtered out) and then back to the veins and heart.

When blood and lymph are in the horse’s legs, gravity takes a toll. Obviously, by this point, the fluids are a long way from the heart and so face an uphill battle to get back up the legs. The horse’s foot plays a vital role in fluid return because the digital cushion’s action helps push the blood and fluid back up the leg.

Therefore, stalled horses and those that don’t move around frequently are at greater risk of stocking up. Additionally, older horses tend to stock up more than their younger counterparts because their circulatory systems don’t work as effectively. Finally, horses with a history of cellulitis are also more likely to stock up than those without, even if it was a one-time event many years ago.

Nutrition’s Role in Stocking Up

A horse’s hydration status can play a role in if and how much he stocks up. A dehydrated horse’s blood pressure might be reduced, which could impair the lymph’s ability to flow back up the leg and result in pooling and edema (fluid swelling). Adequate hydration and sodium balance also impact how fluids move across cells. Therefore, it is possible that dehydrated horses and/or those that haven’t consumed enough sodium could be susceptible to stocking up.

If this is the case, the solution is to improve hydration by ensuring adequate salt intake and fluid consumption. Because you can’t rely on a horse to consume enough sodium from a block, it’s best to provide loose salt (or a good-quality electrolyte supplement) in feed. A 1,100-pound (500-kilogram) horse at rest in cool weather needs about 10 grams of sodium per day—about what 2 tablespoons of salt provides. This amount increases in hot weather and/or when working, which is when an additional electrolyte is helpful.

Other Options

Another way to help prevent stocking up? Try applying standing wraps when your horse is stalled. These apply pressure to the lower limb, which can help keep fluids circulating smoothly.

Involve Your Veterinarian

If your horse’s stocked-up legs don’t resolve in a few days, have your veterinarian out for an exam. Extended periods of edema can cause the skin to stretch or fold, which increases the risk of infection.