Urolithiasis (Urinary stones, Bladder stones)
By Dr Mackie Hobson BSc(Agric),BVSc

1. Diseases

Urinary stones (also referred to as bladder stones, uroliths or urinary calculi) is an accumulation of crystals and cellular debris to form a ‘stone’.  

Obstruction (urolithiasis) occurs in Angora goat ‘kapaters’ and rams and NOT ewes.

The reason kapaters and rams become obstructed is that they have a long and narrow urethra (urinary pipe) which has a number of bends and areas of narrowing when compared to the ewe.

The problem occurs when the stones cause an obstruction and the goat can’t urinate effectively causing urine retention and bladder distension and often ultimately death.

Bladder stones.  (photo vet.uga.edu)                                            Crystal sediment in urine- (photo lockandherd.net.au)

Most common sites of obstruction

(Reference Nancy Walters)

• In the urethral process- a small tube-like extension of skin and urethra at the tip of the penis
• The second most common site is at the “distal sigmoid flexure” — an S-shaped curve in the lower half of the penis.

What causes the stones?

Apart from the anatomy of the male goat a variety of risk factors exist for the development of uroliths.

• Decreased water intake,
• Urinary stasis, retained urine
• Urinary tract infection,
• Vitamin A deficiency,
• High eostrogen intake (Lucerne)
• Lush legume (lucerne) or clover pastures. These forages are rich in calcium, low in phosphorus, and have a high oxalate content. In the gut, oxalate binds calcium avidly and makes it unavailable for absorption. Calcium carbonate and calcium oxalate crystals are less common.
• Diets that are high in grain, phosphorus, and magnesium and low in roughage and that have a low calcium (low Ca:P ratio) will increase the risk of Struvite/Phosphate uroliths

Normally, a ruminant will remove phosphorus from its body by excreting it into saliva and then out through the faeces (manure). High grain, low roughage diets decrease the formation of saliva, so extra phosphorus must be removed from the blood by the kidneys and then excreted in the urine. When diets are too high in phosphorus, the urine phosphorus levels become excessively high, and the phosphorus settles and consolidates into stone-like pellets that can be too large to pass.

Clinical signs

Obstruction, urine retention will lead to abdominal pain, eventual urethral perforation and death due to uraemia.

The obstruction may be partial or complete.

Partial obstruction

• Dribble blood-tinged urine
• Long painful attempts at urination

Complete obstruction

• Strain to urinate
• Tail twitch
• Weight shifting
• Signs abdominal pain

The bladder or urethra may rupture

• The abdominal subcutaneous skin along the penis may become filled and may slough.
• The abdomen may become urine filled (uroperitoneum)
• The goat will not eat, be depressed.

Diagnosis:

• Clinical signs
• Palpation to feel distended bladder or by ultrasound examination
• Calcium oxalate and calcium carbonate can be seen on radiographs but not struvite
• In bladder ruptures fluid obtained by abdominocentesis will have twice the creatinine levels of plasma.
• The abdomen will be symmetrical and pear shaped if urine filled and fluid will be balloted.

Flock Management -Prevention and Treatment

• The salt content of the diet should be gradually increased to promote water intake and produce large volumes of dilute urine (up to 4% of ration)
• Provide excess clean fresh water
• Correct predisposing factors (see ‘what causes stones’ above section.
• Ammonium Chloride can be used to reduce urine pH (7-10g/goat/day for a 30kg goat). This is 0.5-1% of DMI. Molasses should be avoided as a flavouring additive for salted rations, as its high potassium content may diminish the acidifying effect of ammonium chloride

Individual goat treatment

If not obstructed the prognosis is good, once obstructed the prognosis is poor

Partial Obstruction:

• Sedate /anaesthetise the goat to manipulate the stone from the tip of the penis or manipulate it from the urethra. Often recurrence as more stones usually present in the bladder.
• Extend the penis to reduce sigmoid flexure- use of tranquilizers.
• Dose oral ammonium chloride
• Antibiotic as as there is often secondary urinary tract infection
• Surgery (urethotomy) may be required to remove the stone from the urethra and cystotomy to remove bladder stones

Total Obstruction

• establishing a patent urethra
• correcting electrolyte imbalances (valuable animals)
• Surgical possibilities

• Urethral Process Amputation:

The urethral process is a very short, narrow tube-like structure on the tip of the penis, and because of its location and size is the most common site for uroliths to obstruct. “Amputation” or removal of this process with a scalpel blade may allow uroliths within this process to pass, but recurrence of obstruction is likely, particularly if uroliths are also present higher up in the urethra. If this is the case, additional surgical procedures are needed.

Urethral process marked by arrow (Photo www.avcs.org)

• Perineal Urethrostomy:

The urethra and its surrounding tissues can be easily felt in the back end (“perineum”) of sheep and goats 2-3 inches below the anus and just behind the rear legs. When uroliths block the penis or when the urethra has ruptured downstream from this area, a new opening can be made in this location to allow the animal to urinate like a female. This procedure is sometimes performed under heavy sedation with regional anesthesia (nerve blocks), but in valuable animals or pets it is often performed under general anesthesia. An incision is made through the skin and into the urethra, and the new urethral opening is sewn directly to the skin. The animal then urinates down and backwards instead of forwards. The problem is that the ram is no longer able to reproduce!

Cystotomy and dietary management in valuable animals

What are the different type of stones?

• Silica
• Magnesium ammonium phosphate (phosphatic, struvite) - have the appearance of sand.
• Calcium carbonate- are round in appearance and have a characteristic dull gold colour
• Calcium oxalate – are round in appearance

 Calcium Oxalate stones (photo pethelpful.com)                                 Calcium oxalate under microscope (photo studyblue.com)

Calcium carbonate crystals - microscope (photo eclinpath.com)        Struvite crystals under microscope