Each horse has a different pattern of urination — when, where and how much he pees.
Normal urine production is typically 15-30 ml/kg daily, which for an average 500kg horse totals around 15 litres. Measuring urine output is not easy, in practical terms, but this equates to a horse peeing around five or six times per day, with a normal stream of urine lasting 30 seconds.
A healthy bladder holds 300-400mls of urine. We have to assume that a horse with a full bladder will feel uncomfortable and may lack concentration, so ideally he will pee before he competes. Ways of encouraging a horse to go at home, before a short journey, include walking him out on to grass or moving him on to fresh bedding. Some can be trained to urinate in response to whistling or even when a bucket is produced.
Long journeys are more challenging, as some horses will not urinate on the lorry — especially geldings, who may worry about having insufficient room to stretch out or that urine will splash on their legs. If a horse won’t go when he gets to the venue, try unloading him on to grass, spreading new straw or shavings on the lorry floor or even hiring a stable so you can lay down some new bedding.
More often than not, a horse will pass urine before he suffers any significant ill-effects. On occasion, however, he may experience more than discomfort by holding it in. A full bladder bouncing off the pelvic bones during strenuous exercise has been reported to cause bladder damage and blood in the urine, especially if there are abnormal bony protuberances in the pelvis.
In full flow
Urination allows the body to eliminate waste, so the urinary tract — the kidneys, ureters, bladder and urethra — also plays an important role in electrolyte balance, blood volume and regulation of blood pressure.
Urine is typically straw-yellow to pale brown in colour and may be cloudy due to the mucus and calcium carbonate crystals present. A horse with free access to water tends to have paler urine, while an animal in hard work and possibly sweating a lot, in hot weather, may produce more concentrated and stronger-smelling urine that is darker yellow or brown. A natural oxidation process can turn urine red-brown — this is particularly noticeable on a bed of new shavings and can be mistaken for blood in the urine.
Urine should stay the same colour throughout the stream. The timing of any discolouration should be noted — knowing whether it changes at the beginning, middle or end of the stream can help to locate the problem.
Consistent discolouration is usually indicative of myoglobinuria (muscle damage) caused by the condition tying up, or could be a sign of atypical myopathy caused by sycamore poisoning. Abnormal colour at the beginning or end of the stream may indicate a lesion in the urethra, or, in a stallion, the accessory sex glands.
Blood in the urine is a serious concern and requires veterinary attention. Kidney infections are uncommon in adult horses, but blood may be a sign of cystitis, which is more common in mares because of a shorter urethra. Bladder or urethral stones (calculi) can cause partial obstruction during urination; the horse may try to pee repeatedly but only pass small amounts, usually with some blood present.
By knowing what’s normal for your horse, you’ll be more tuned in to any changes that may be a cause for concern.
Ref Horse & Hound; 11 July 2019