Equine Disease Quarterly | EQUINE
over an eight-year period (2010-2018) were queried
for diagnoses related to renal pathology. Equine
fetuses, foals, and adults of a variety of breeds were
included. It was determined that 3.6% (386/10,541) of
equine submissions had some type of renal pathology.
Of those diagnoses, renal lesions were determined
to be primary in 38% of cases (n=148), secondary to
another process in 55% of cases (n=211), or incidental
in 7% of cases (n=27).
Significant processes associated with primary
lesions included: inflammatory/infectious (95 cases);
congenital (21 cases); neoplastic renal carcinoma/
adenocarcinoma (10 cases); nephroliths (10 cases);
toxic (four cases); trauma (one case); and other
miscellaneous (i.e. chronic renal failure, protein losing
nephropathy) conditions (seven cases).
Within the infectious/inflammatory group, the
most common cause was a bacterial pathogen
resulting in nephritis. The largest proportion of
cases was due to Leptospira interrogans infections
in fetuses. Leptospirosis is a cause of abortion that
often localizes to the kidney. Actinobacillus equuli
was another common bacterial isolate, most often
seen in neonatal foals and occasionally adults. In
foals, infection with A. equuli is colloquially termed
“sleepy foal disease.” Routes of infection for A. equuli
include a contaminated umbilicus, inhalation or
ingestion. Several cases of bacterial pyelonephritis
were identified. Pyelonephritis is inflammation of the
renal pelvis that most often results from an infection
that extends up to the kidneys from the lower urinary
tract (i.e. urinary bladder). The most common bacterial
isolates identified from cases at the UKVDL included
Streptococcus zooepidemicus, Escherichia coli, and
Enterococcus sp.
Lesions that comprised the congenital category included
renal dysplasia, renal agenesis, congenital renal cysts
or congenital hydronephrosis/hydroureter. While
there have been proposed associations of hereditary
or nutritional components for developmental renal
abnormalities in some species (i.e. dogs and pigs), in
horses the pathogenesis of these congenital lesions
remains to be elucidated.
Significant nephroliths (kidney stones) were identified
in 10 horses. The stones were composed of calcium
carbonate or a mixture of calcium carbonate with other
minerals. Typically, horses with nephroliths remain
asymptomatic until the stone results in obstruction.
Development of nephroliths has been associated with
any nidus of renal disease including cysts, papillary
necrosis, pyelonephritis or neoplasia.
Papillary (medullary crest) necrosis due to suspected
long-term use of non-steroidal anti-inflammatory
drugs (NSAIDs) was identified in three of the four cases
in the toxic category. NSAIDs (i.e. phenylbutazone/
bute and flunixin meglumine/ Banamine) are routinely
used in horses for pain management. NSAIDs
work by inhibiting a specific group of enzymes,
cyclooxygenase (COX), which subsequently reduces
inflammation. Unfortunately, other downstream
effects of this pathway include decreased production
of prostaglandins. Specific cells located in the renal
medulla produce prostaglandins that are mediators
of blood flow to the tissue. Therefore, decreased
prostaglandin production results in impaired blood
flow to the medulla and subsequent necrosis. Other
compounding factors include dehydration and use of
multiple NSAIDs. Luckily, renal complications due to
NSAIDs are well described with the result that there is
judicious use of these medications in practice.
The equine kidney has a vital role in overall health. A
variety of disease processes can impair renal function.
Awareness of these diseases is important for equine
health.
• Volume 21 Issue 1 | March 2019 •
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