Question

I care for a 12-year-old Warmblood. He produces excessive urine (his urine stream is clear) and drops quite a bit. He seems uncomfortable at times under saddle. Once he urinates, he seems comfortable again. He is being tested for diabetes and other medical issues. Any ideas? The owner is quite concerned and I am thinking a dietary change might help.

Answer

Unusually frequent urination occurs for many reasons, some medical and some dietary. Because your horse’s veterinarian is doing a thorough evaluation of possible medical issues (considering insulin resistance, kidney disease, and Cushing’s disease, for example), I will address the nutritional possibilities.

Excessive protein in the diet can cause a horse to urinate more than usual because the body is breaking down large quantities of protein. In processing protein, the nitrogen molecule is split off from the the protein so that the nitrogen-free part can be used for energy. The nitrogen fraction must be removed from the body because a buildup can be toxic. Nitrogen is diluted with water to form urea to minimize its effect on the body and is then filtered out of the bloodstream by the kidneys.

Instances of excessive protein in the diet are characterized by a noticeable increase in water intake and urine production. Feedstuffs high in protein include alfalfa (lucerne), clover, and other legumes, as well as soybean and canola meals and peas. Fed in small quantities, these feedstuffs will not cause a problem, but when overfed problems can occur.

If the horse is out on pasture, there are certain plants that may cause excessive urination. Clover is the most obvious but grasses like millet and some sorghum types (especially Johnsongrass) contain toxins that overwork the kidneys and possibly cause cystitis.

If a horse has an excessive obsession with salt and eats well above its requirement, it will also cause the horse to drink a lot more water. Too much salt in the body triggers the thirst response, which is the physiological prompt designed to dilute and flush out excessive salt. The body will get rid of the excessive sodium and chloride through urination.