South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
muscle mass, hydration and degree of azotaemia but is usually >10 (mg/dL units). Mild
hyponatremia and hypochloremia may accompany CKD but serum concentrations of these
electrolytes can often remain within reference ranges. Hypercalcemia, with serum concentrations
sometimes approaching 20 mg/dl (5 mmol/L), appears to be a laboratory finding that is unique to
horses with CKD. Hypercalcemia is not a consequence of hyperparathyroidism as parathormone
concentrations are not elevated in horses with this finding. The magnitude of hypercalcemia is
dependent on diet and high values can return to the reference range within a few days of changing
from alfalfa to grass hay. Acid-base balance usually remains normal until CKD becomes
advanced but metabolic acidosis may be found in horses with end stage disease. Many horses with
CKD are moderately anemic (packed cell volume 25-30%) likely due to decreased erythropoietin
production. Horses with glomerulonephritis may have hypoalbuminemia and hypoproteinemia
while horses with advanced CKD of any cause may also have mild hypoproteinemia associated
with intestinal ulceration.
Urinalysis findings may also vary depending on the cause of CKD. As mentioned, urine is
relatively devoid of normal mucus and crystals making samples transparent. Further, a hallmark
of CKD is urine specific gravity in the isosthenuric range (1.008 to 1.014), although heavy
proteinuria in an occasional horse with glomerulonephritis may produce values up to 1.020.
Quantification of urine protein concentration is required to accurately assess proteinuria. Urine
protein concentration in normal horses is usually less than 100 mg/dl and the urine protein to Cr
ratio should be less than 0.5:1. With significant proteinuria, urine protein to Cr ratio is usually
greater than 1:1. Horses with chronic interstitial nephritis usually do not have significant
proteinuria.
Diagnosis of chronic kidney disease: A diagnosis of CKD is most commonly made in horses
with azotaemia and isosthenuria that present with a complaint of weight loss and/or decreased
performance. Concurrent detection of hypercalcemia also strongly supports CKD. Rectal
examination may be helpful. Horses with ureteral calculi, often have enlarged ureters that can be
palpated as they course through the retroperitoneal space. Although kidneys of horses with CKD
are typically small with an irregular surface, these changes are not always apparent on palpation
of the caudal pole of the left kidney. Ultrasonographic imaging is extremely useful for evaluating
kidney size and echogenicity and may reveal fluid distention (hydronephrosis, pyelonephritis, or
polycystic disease) and/or presence of nephroliths. Horses with significant renal parenchymal
damage and fibrosis often have increased echogenicity of renal tissue that may be similar or even
greater than that of the spleen.
Treatment of chronic kidney disease: Treatment of horses with CKD is most likely to produce
improved renal function if there is an acute, reversible comp onent exacerbating CKD (acute on
chronic syndrome). If an acute component is detected, it should be corrected rapidly (as described
for AKI/ARF) with the goal of minimizing further loss of functional nephrons. Further, surgical
removal or fragmentation of stones via lithotripsy may be indicated in horses with calculi that are
thought to be causing obstruction of urine flow. Treatment of horses with stable CKD consists of
supportive care: providing sufficient water, electrolytes, and nutritional support. In addition to Cr,
serum electrolyte concentrations and acid-base balance should be measured regularly. Although
no adverse effects of hypercalcemia in horses with CKD have been documented, decreasing
calcium intake (replacing alfalfa or other legume hays with grass hay) may result in a return of
serum calcium concentration to the normal range. NSAIDs are best avoided in horses with CKD.
Nutritional management aimed at maintaining body condition is the most important aspect of
supportive care of horses with CKD. Access to good quality pasture, increasing carbohydrate
18