Renal Disorders of Equine Neonates

The equine neonatal kidney is reasonably mature in its ability to excrete electrolytes (except Na), and excrete drugs via glomerular filtration[1].
Editor's Comment - This means that neonatal foals are NOT more sensitive to aminoglycosides like gentamicin and Amikacin than adults provided they are not dehydrated.

I. Etiology of Renal Disease in Equine Neonate

1. Pre-renal cause due to inadequate perfusion of functional kidneys is the most common condition

1. Dehydration - Sunken eyes, poor pulse.
2. Asphyxia damage occurring during cesarean section, dystocia, induction of parturition
3. Diarrhea, inadequate fluid intake.

2. Renal causes are primarily due to Gram negative sepsis causing inflammatory foci, bacterial colonization of the kidney, and tubular necrosis from prolonged reduced renal blood flow and ischemia associated with shock, enteritis or surgical and gastrointestinal problems. Fibrin may also deposited in the renal capillaries and glomeruli due to DIC. with rate and severity of erythrocyte destruction.

1. Neonatal isoerthyrolysis can produce hemoglobin nephrosis.
2. NSAID drugs accompanied by hypovolemia may significantly reduce renal blood flow
3. Aminoglycoside toxicity is uncommon if hydration is maintained in ill foals. Ill foals treated with aminoglycosides and undergoing anesthesia may be most susceptible to aminoglycosides.
4. Tetracycline overdose associated with attempts to treat contracted tendons has been observed.

3. Post-renal causes include, urachal tearing, urethral obstruction, ruptured bladder, ureter rents.

1. Ureter defect in foals aged 5-6 days - Off feed, urinalysis normal, peritoneal tap normal, post renal azotemia, vaginal edema, perineal edema, swollen sheath. Urine accumulates in retroperitoneal space; bilateral defect adjacent to kidney. May be repairable.

II. Clinical Signs and Diagnosis

1. Oliguria is uncommon with acute renal failure in neonates.

1. Foals produce approximately 6-10 ml/kg/hr of urine
2. Catheterize bladder to confirm after IV fluid treatment.
3. Lasix to induce urine formation.
4. Dobutamine drip at 2-10 µg/kg/min IV.
5. Norepinephrine at 0.1-1.5 µg/kg/min IV.

2. Specific clinical signs may not be seen but suspect renal involvement with sepsis, dehydration, prematurity and other disorders.
3. Creatinine levels [2]

1. Some <24 hour old foals without severe renal disease can have elevated serum creatinine concentrations (4-23 mg/dl). Cause is usually placentitis and creatinine is lower on day two and drops over 3-5 days to normal (<2 mg/dl).
2. A single elevated serum creatinine determination is not diagnostic. However, serial determination over several days with fluid support and rising creatinine is indicative of renal disease or post renal problems.

4. BUN levels rise with renal disease. Values on day 1 and 2 reflect maternal levels.
5. Urinalysis [2]

1. Caution must be used because the normal foal values are distinctly different than adults. Normal equine neonate has proteinuria for first 36 hours of life, urine pH 6-7, and specific gravity 1.001-1.012.
2. Mild hematuria can be seen nonspecifically in sick foals.
3. Abnormalities are > 2 + occult blood, casts, bacteria and leukocytes.
4. Fractional excretion of electrolytes has been estimated in a limited number of foals <7 days of age, on a milk diet FxNa 0.31% ± 0.18, Fx K 13.26% ± 4.49, Fx PO4 3.11% ± 3.81 [3].
5. Urine Gamma GT/creatinine ratio 12.5-46.15 in normal foals <14 days of age [2].
6. Urine volume produced is ∼148 l/kg/day [3].

III. Management of Renal Disease

1. Provide adequate fluids by oral or intravenous route. Weigh foal twice daily and observe for overhydration.
2. Determine if post-renal problems exist.
3. Avoid NSAID if possible.
4. Limit sodium and potassium containing fluids because foal has limited ability to excrete - Monitor serum levels.
5. Modify dose of aminoglycosides
6. Hyperkalemia (life threatening) may be treated with:

1. Sodium bicarbonate 1-2 mEq/kg IV over 30 minutes.

1. Check pH and be sure foal is ventilating

2. Calcium gluconate 10% 0.5-1.0 ml/kg IV over 15 minutes.
3. Glucose infusion 5% IV 100 ml over 15 minutes.
4. Glucose IV plus 0.1 units of insulin/kg (regular insulin).

1. Closely monitor for hypoglycemia.

5. Sodium polystyrene hapsulfonate exchange resin 15 gms/100 ml of 10% dextrose via enema. Monitor serum K+ and Na+closely.

IV. Congenital Problems

Some of the signs of gastroduodenal ulcers in foals vary with the clinical syndrome.

1. Bilateral renal dysplasia with nephron hypoplasia [4].

1. Depression and lethargy at <48 hours of age
2. Hyponatremia, hypochloremia, azotemia, hypoproteinemia.
3. Urinalysis - 1+ blood, 3+ proteinuria, increased FE Na, increased GGT/Cr ratio
4. Renal biopsy - Tubular hypoplasia with secondary necrosis.
5. Ultrasound - Cystic appearing lesions

2. Renal hypoplasia and dysplasia

1. Disease may manifest in neonatal period.