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Urinary Calculi
by Jennifer Maas, DVM
This year I’ve seen
several cases of urinary obstruction in male sheep and goats. A
four-month-old Nubian wether underwent successful surgery, one
ram lamb was put to sleep because his urethra had ruptured, one
mature breeding ram was put to sleep because of suspected
urethral rupture and one yearling ram’s urethral process was
snipped to free the obstruction. A four-month-old Pygmy wether
who was unblocked by snipping the urethral process went on to
block higher up in the urethra, thus necessitating a
urethrostomy.
Almost any time a client
calls concerning a male sheep or goat with the complaint, “My
animal is depressed, won’t eat, looks bloated, acts
constipated, and is straining,” my thoughts jump to a blockage
of the urethra, the tube leading from the bladder to the penis
which passes sperm and urine, with urethral “calculi”, small
stones from the bladder which lodge in the long, thin male
urethra.
Usually, when I arrive,
the animal is down, had abnormally dry hair around the penis,
and is lying in an unusually dry stall. Because of the buildup
of urea and other toxins that are normally passed in the urine,
the animal is quite depressed. A combination of decreased water
intake and increased blood toxin level causes the animal to
also be dehydrated.
If the animal is not
castrated, I can extrude the penis and check the small,
worm-like urethral process at the end of the penis for buildup
of the small stones. This is a common site of obstruction since
it is quite small. In the castrated animal, especially in one
castrated at a young age, the attachments of the penis to the
prepuce have not yet broken down and sometimes it is impossible
to examine or extrude the end of the penis. If there are
crystals in the urethral process, easily seen and felt on the
exam, I can snip off the end of the process with a sharp pair
of scissors, thus often ridding the animal of the blockage.
This must often be done under light anesthesia, especially when
dealing with goats. Obtaining a good stream of urine is surely
a relief once the urethral process is snipped, but the animal
may very possibly become reblocked with stones higher up, even
if this is achieved.
If the urethral process
cannot be visualized and/or the blockage doesn’t occur at this
point, then either surgery or euthanasia should be considered.
If surgery is the decision, it should be performed promptly,
before the animal becomes more toxic.
I must convince myself
the problem is a urethral obstruction. This can sometimes be
done by feeling a large abnormally hard bladder. If the bladder
can’t be felt and obstruction is suspected, a ruptured bladder
should be ruled out by tapping the abdomen with a hypodermic
needle and checking for urine spillage into the abdominal
cavity. A high blood urea and blood creatinine can also tell
me, especially in the case of a large animal whose bladder is
difficult to feel, whether I am dealing with a probable urinary
obstruction.
The other common site of
blockage is a point at which the urethra make an S-shaped
curve, the sigmoid flexure. The sigmoid flexure frustrates all
attempts at passing a catheter from the penis to the bladder
because of it’s curvature. If the blockage occurs at this
point, the only solution is to do a urethrostomy. This involves
making a longitudinal incision over the urethra at a site below
the anus, suturing the opened incision to the skin and allowing
it to heal open, thus causing a permanent hole in the urethra
where urine crystals can pass freely. Surgery is done under
general anesthesia and is fraught with complications after the
surgery, mainly consisting of the urethra scarring shut or
stricturing at the surgical site. The success rate is probably
about 50%. This surgery is useful only to save the animal’s
life, but not to salvage it as a breeding individual.
Causes and Prevention:
Urolithiasis or calculosis, the metabolic disease of male sheep
and goats, is the blockage of the urethra by struvite crystals,
preventing the normal passage of urine from the bladder. The
disease, caused by what appears to be a complex of dietary and
environmental factors, begins with the formation of ammonium
phosphate ions which form a nidus to which other ions and
eventually cells and mucus from the bladder adhere, forming a
calculus of up to 3 mm in diameter. These calculi pass without
problem through the large, short female urethra, but rub and
irritate the lining of the long, thin male urethra, causing
irritation, swelling and eventual obstruction and occlusion of
urine outflow.
Males from a few weeks of
age to mature rams and bucks are all susceptible to this
noncontiguous disease, but the highest risk population is the
wether 3-6 months old on a high concentrate diet who has been
castrated at an early age.
Factors which appear to
predispose to the formation of urinary calculi:
-
A high percentage of
concentrates (grain) in the diet.
-
A high phosphorus to
calcium ratio.
-
Castration at an early
age (1-4 weeks), slowing growth and development, resulting in
a juvenile penis and urethra (narrower lumen and persistent
adhesions of the penis to the prepuce)
-
Water deprivation.
-
Inclement wether:
Prevention of this deadly
metabolic disease involves:
-
Castration after the
animal is a month old.
-
Feeding a 2:1
calcium/phosphorus ratio rather than offering minerals free
choice.
-
Adding sodium chloride
to the diet so that it constitutes 4% of the dry matter in
the diet. This will aid by discouraging the formation of
crystals through its ionic action, and by increasing the
animal’s water intake.
-
Offering the animal
plenty of warm, fresh water.
Finally, it is extremely
important to avoid over-feeding your male goats. Castrated or
not, a male goat does not need anywhere near the concentrate
required by a milk producing doe. Although a young animal needs
concentrate, care should be taken not to over-feed the young
male. As long as good quality hay is fed, concentrate should
figure only marginally in the diet of the mature animal.
Excerpts from:
Kinne, Maxine, ed.
Pygmy Goats: Best of Memo
2
(1982-1987)
National Pygmy Goat Association: pp 147-148
This document is for
informational purposes only and is in no way intended to be a
substitute for medical consultation with a qualified veterinary
professional. The information provided through this document is
not meant to be used in the diagnosis or treatment of a health
problem or disease, nor should it be construed as such.
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