by Dr. Jennifer H Stewart BVSc BSc PhD Dip BEP
Equine Veterinarians Australia
What are bladder stones ? Bladder
Ureter
Kidney
Urethra
Credit to MSD
Male horse anatomy
HOW: Under certain conditions, dead cells, proteins and minerals that are normally washed out with a horse’s urine collect to form tiny crystals. Additional cells and debris then become attached to one or more of these crystals to form larger, rocklike masses. If these get big enough, they remain trapped in the bladder, where they can block the entry to the urethra and prevent the outflow of urine. WHAT: Most of these stones are composed primarily of calcium carbonate, but other minerals, such as magnesium and phosphorus, may be included as well. WHO: Male horses are much more likely to develop bladder stones than mares are because of differences in their anatomy.
Stones in your horse’s urinary tract . While stones in the horse’s urinary tract are uncommon and usually respond well to prompt treatment, the signs and symptoms of one or more stones can be mild, vague and easily missed. Signs occur when the stone or stones (known as uroliths) intermittently obstruct the outflow of urine and/or cause trauma and inflammation to the bladder wall. During exercise, the stone/s can bounce around and traumatise the bladder wall, causing blood in the urine after exercise.
Where the stone/s cause a complete obstruction it is very painful for the horse and they pass very little urine. These horses are at risk of bladder rupture, which is a life-threatening complication Continued and can be expensive and difficult to treat.
Kidney stone
Ureteral stone Bladder stone
WHERE: Urinary stones in horses are named based upon the location of the stone. When located in the bladder, they are referred to as cystoliths, when found in the kidney, they are referred to as nephroliths, in the ureter they are ureteroliths and when found in the urethra they are urethroliths. The presence of these stones can cause urinary problems for the horse, which can lead to urinary tract infections as well as urinary flow obstructions, which can ultimately lead to kidney failure and death if not treated.
Table 1. Signs That May
Indicate a Suspision of
URINARY TRACT STONES Painful or uncomfortable urination Unusual urine consistency or appearance Reduced volume of urine Thick, cloudy urine Bloody urine Pus in urine Blood clots in urine Particles in urine Scalding around the perineum in mares Scalding on the inside of the hindlegs in geldings and stallions Protrusion of the penis Dribbling of urine Recurrent mild colic Abnormal hindlimb gait Urinating too much Urinating too little Drinking too much Straining to urinate Mouth ulcers Change in appetite or attitude Behaviour problems (e.g. bucking) when ridden Passing frequent small amounts of urine Blood in the urine after exercise Stretching before and after urination
Because bladder stones can quickly become a veterinary emergency, any horse showing signs of stones in the urinary tract (urolithiasis) should be seen by a veterinarian as soon as possible. Stones (also known as calculi and uroliths) are much more common in males of every species because of their longer, less ‘stretchy’ (distensible), narrower urethra. Seventy-five percent of cases occur in geldings and stallions. Mares can generally pass small stones before they become large enough to cause a problem. In horses, the most common location for a stone to form is the bladder. But they can occur anywhere in the urinary tract. In one study of 64 horses with urolithiasis, stones were in the bladder (cystoliths) in 47 horses, urethra (urethroliths) in 11 horses, kidneys (nephroliths) in 15 horses and ureter (ureteroliths) in two horses. They occurred at several sites in six horses and seven horses suffered recurrent stones after treatment. Left: A bladder stone, showing approximate size. Below: Figure 2. Bladder Stone seen within the bladder via cystoscopy Image courtesy of University of Florida.
The Cause The cause of bladder stones in horses is not fully understood but they seem to be dependent on a number of factors including: urine retention, concentrated urine, vitamin A deficiency, excess dietary vitamin D and genetics. Two types of stones occur and both are believed to be formed as a result of the normal shedding of bladder lining cells and mucous in the bladder. Stones often start with a ‘nidus’ or a cluster of cells. These cells may be part of the normal bladder cell turnover, or secondary to a urinary tract infection or kidney damage from drugs like phenylbutazone and flunixin. Infection is usually a secondary problem, but damage to the bladder lining as a result of inflammation (cystitis) could allow the retention of organic matter that acts as a nidus for crystals to adhere to. Once that cluster of cells is there, layers of mineral keep getting deposited until a stone is formed (similar to a pearl forming in an oyster).
We might think bladder stones in horses would be a common problem due to the large amount of minerals in normal equine urine, but that is not the case. Although bladder stones are a concretion of minerals - primarily made up of calcium - heredity, diet and bacterial infection are often related to the development of stones. Although infection is not thought to be a cause of stones, it may be significant in creating circumstances where crystals begin to form and may cause them to increase in size. The different types of stones found in different species relates to their diet and urine pH. Horses have a lot of calcium and mucus in their urinary tract. That calcium and mucus is why even normal horse urine is often cloudy. Your veterinarian can diagnose stones by means of palpating the bladder rectally, ultrasound of the bladder, and/or endoscopic (camera) exam of the urethra and bladder (Figure 2 left ). Stone size ranges from 1.5 – 20cm and the time it takes for them to develop is not known. Removal usually requires surgery and your veterinarian can advise on the various methods.
February/March 2021 - Page 24
Any tricks you can use to keep your horses drinking lots of water will help prevent stone formation. day), ammonium chloride (25-50g twice daily) or ammonium sulphate (175g twice daily). Encouraging drinking to keep urine forming and flowing freely is critical in hot weather especially in exercising horses. Salt and fibre both stimulate drinking.
Other causes of stones and blood in the urine How can bladder stones be prevented? Keeping urine dilute may help prevent stone formation. So any tricks you can use to keep your horses drinking lots of water will help (dampening feed, ensuring salt intake is maintained especially after sweating or hard exercise) and minimising use of drugs like Bute that can be damaging to the kidney will also help. While not necessary for every horse, if your horse has recurrent stones, not overfeeding protein, beet pulp, legume hays and chaffs, and bran (high in phosphorus) may be beneficial in reducing mineral overload. Your veterinarian may advise urinary acidifiers like vitamin C (10-20g twice a
Although horses are unique in that they excrete excess dietary calcium through their urine instead of manure, reduced kidney function in older horses and those with reduced liver or kidney function can result in kidney (renal) stones, bladder stones, weight loss, and loss of appetite. If kidney function is reduced, renal and bladder ‘stones’ of calcium oxalate are more likely to occur – especially in horses grazing oxalate-containing pasture. (These include pastures like kikuyu, buffel grass, setaria, green panic, pangola grass, guinea grass, purple pigeon grass, para grass and signal grass; the soluble oxalates in the grass can be absorbed into the blood stream and deposit in the kidneys where they form calcium-oxalate crystals and lead to kidney damage).
Mares: Although rare in horses, inflammation of the bladder (cystitis) is more common in mares than geldings or stallions. It can occur when a urinary tract infection ascends, or a kidney infection
Continued
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Bladder Stones continued...
descends to the bladder. Damage to the nerves and muscles of the mare’s bladder or urethra can occur during foaling. If the muscles are unable to completely empty the bladder, sediment can accumulate causing inflammation of the bladder wall and initiate stone formation. It is not often outwardly apparent that the bladder is inflamed, but other signs of cystitis may be present include: excessive urination, excessive posturing to urinate, blood in the urine, or dribbling of urine without full voiding of the bladder. Treatment varies on a case-by-case basis depending on the cause; for example if the bladder inflammation is due to an underlying vaginal infection, the vaginal infection must be treated before the cystitis will go away without recurrence. Prompt veterinary diagnosis will improve the outcome and speed of recovery and reduce the risk of further complications.
Male horses: Smegma (a natural secretion of a pastylike material from the sheath) can form a ‘bean’ at the tip of the penis. Routine sheath cleaning prevents the bean from growing large. Large beans can cause difficulty urinating and sheath swelling. Excessive smegma accumulation is more common in stalled horses, possibly because of lack of exercise and accumulation of shavings and stall debris in the sheath. However, routine veterinary inspection of this area is important because tumours and other diseases of the sheath are relatively common. Also, vets often tranquilise horses before cleaning their sheath to relax the penis and make it easier to completely remove all debris. The presence of blood in the urine is more common in competition horses – whether racing, dressage, showjumping or other intense forms of training and exercise.
As exercise intensity increases and more blood is directed to the muscles, heart and lungs, kidney blood flow is reduced (especially in the presence of dehydration) and red cells can leak into the urine. Trauma to the bladder lining occurs in humans as well as equine athletes. As the horse’s body moves, the bladder flops backwards and forwards and can get bruised and leak blood and blood clots into the urine. This should resolve in a day or two. If it doesn’t a prompt veterinary examination is indicated. Blood in the urine has been described in high-level dressage horses. Termed ‘equine idiopathic haemorrhagic cystitis’, it is associated with thickening of the bladder wall and blood leakage into the urine. It is thought to be related to exercise intensity. In humans, urinary stones are attributed to a faulty diet and insufficient water intake to flush calcium through the system. The horse’s physiology is very different from humans. Bladder stones are rare in horses because the horse has evolved to excrete minerals through the kidneys. Horses are able to regulate the amount of calcium carbonate they produce, but any breakdown in the protective regulatory systems could increase risk and modifying the diet alone does not necessarily reduce the risk. One of the most important protective strategies in horses is the ability to posture and void the bladder at will frequently. Discouraging horses from urinating is dangerous. Formation of a stone is often bad luck — a random piece of debris in the bladder that acts as a ‘nidus’. Stones can also develop in the kidney and fall into the bladder.
Because there is no way to prevent stones, it’s really important to be vigilant about changes in urinary habits, especially in male horses. Pay attention to the colour and frequency and amount of urine produced, collect a sample if you’re concerned. With prompt veterinary intervention and correct dietary, salt and fibre intake after a stone has been removed, the prognosis is good. All content provided in this editorial is for general use and information only and does not constitute advice or veterinary opinion. The content does not consider individual circumstances, is not intended as a substitute for advice, and should not be relied upon as advice or in place of consultation with your equine veterinarian. For full disclaimer, please refer to our website: www.jenquine.com.au
Exercise-induced blood in the urine Often not visible to the naked eye, exercise-induced blood in the urine (haematuria) is very common but under-recognised. Microscopic examination of urine from horses exercising at 40% of maximum capacity found over 85% had red cells in the urine. One hundred percent of horses exercising at 95-100% had red cells in the urine. The cause of exercise haematuria is not well understood and may vary with the type and duration of exercise. The kidney blood supply can be compromised by contact (polo and rodeo horses) or from shaking and jostling (racing, endurance, jumping, reining, cutting, driving and most other equine activities). February/March 2021 - Page 26
Dr Jen Stewart has been an equine veterinarian for more than 40 years and an equine nutritionist for more than 20 years. Jen has been developing premium formulas for studs, trainers and feed companies - such as Mitavite - in Australia and around the world. Consulting to leading international studs and trainers in various countries while working on research projects and being involved in nutritional management of a variety of equine clinical conditions, including colic, tying-up, laminitis, performance problems, developmental orthopaedic diseases and post-surgery. Dr Jen is currently the only practicing equine veterinarian and clinical nutritionist in Australia and was also an official veterinarian at the Sydney Olympics 2000. Jen’s passion for nutrition along with her extensive experience and knowledge strives to continue to BRING SCIENCE TO YOUR FEED BIN.
Dr Jennifer Stewart CEO BVSc BSc PhD Dip BEP Equine Veterinarian and Consultant Nutritionist.
Dr Jennifer Stewart www.jenquine.com Equine Veterinarians Australia www.ava.com.au