anuric sheep SDL

Question 1

what is urolithiasis

Answer 1

Stones or calculi in the urinary tract

Question 2

Based on the anatomy of the ovine urogenital tract, state the most likely sites that the urinary tract may have become blocked with uroliths in this case. Why is blockage likely at these sites? Are any of these sites unique to the sheep?

Answer 2

Calculi are most likely to block at either sites of narrowing or changes of direction
In rams, three sites are common
The sigmoid flexure (changes of direction, Dyce, page 717, also common in cattle) See image below
The glans penis (narrowing)
The vermiform appendage or urethral process (narrowing, unique to sheep and goats, Dyce page 719)

Question 3

Is obstructive urolithiasis more or less likely in female sheep? Why?

Answer 3

Urolithiasis is just as likely in female sheep, however obstruction in much less likely because the urethra is shorter, straighter and wider

Question 4

What are the potential consequences of urolithiasis if it is not successfully treated?

Answer 4

Urine continues to be produced, gross expansion of the bladder, causing signs of discomfort, continuous effort (straining) to pass the calculi
Eventually the bladder rupture, initially this leads to an improvement in condition before the toxic effects of urea are seen. The renal pelves and ureters are commonly dilated because of the back pressure

Question 5

how is urolithiasis treated in sheep

Answer 5

Amputation of the vermiform appendage (if blocked) with a pair of scissors (very quick and easy, the appendage is literally just snipped off). Very quick, easy and effective. No implication for the future fertility.
Catheterisation of the urethra to the bladder is basically impossible in male ruminants because of the sigmoid flexure; retrograde flushing does not work
Smooth muscle relaxants to increase the diameter of the urethra – No evidence they work clinically
Surgery (usually the key treatment option if the urethra is blocked proximal to the vermiform appendage).
Please note there is no expected negative consequence on subsequent fertility of removal of the urethral process.
Perineal urethrostomy: The penis is approached surgically just beneath the anus, transected and exteriorised under general anaesthesia or local anaesthesia (more likely in sheep). No use in this case because the ram will not be able to breed
Many more surgical options if this were a cat or dog, cost and outcome are limiting in this case