Renal dysplasia in horses: 25 cases (1991-2021).

Overview

• This study describes the clinical features, laboratory findings, and histopathology of renal dysplasia (RD), a congenital kidney malformation, in 25 horses of various breeds and ages examined between 1991 and 2021.
• The researchers found RD occurs in horses from newborns to adults, with particular overrepresentation in Paint and Miniature horses, and that clinical severity varies widely.

Background and Purpose

• Renal dysplasia (RD) is a congenital malformation of the kidney with varied clinical signs and limited characterization in horses prior to this study.
• The authors hypothesized that RD occurs in horses of many ages and may be more common in certain breeds.
• The primary objective was to describe clinical signs, laboratory data, ultrasonography, and histopathological findings in horses diagnosed with RD.

Methods

• The study was a retrospective case series reviewing medical records from a veterinary teaching hospital over 30 years (1991-2021).
• It included 25 horses diagnosed with RD, spanning a broad age range (0 days to 24 years), multiple breeds, and both sexes.
• Data collected included clinical signs, blood and urine laboratory results, ultrasound exams, treatments, outcomes, and microscopic examination of kidney tissue.
• Breed prevalence among affected horses was statistically analyzed using Fisher’s exact test to identify overrepresented breeds.

Key Findings

• Prevalence in Breeds: Paint horses and Miniature horses were strongly overrepresented among RD cases, with odds ratios of 21.3 and 12.9 respectively compared to other breeds (P < .0001).
• Age and Distribution: RD was found across all age groups from newborn foals to older adults; approximately 44% of cases were incidental findings identified at necropsy (postmortem exam).
• Laterality and Severity: 84% of cases had RD in both kidneys (bilateral), and 68% showed diffuse involvement of kidney tissue.
• Clinical Signs: Clinical symptoms were more common and severe in neonatal foals, including:
  • Azotemia (elevated blood nitrogen waste products) in 64% of neonates
  • Hyponatremia (low blood sodium) in 37% of neonates
  • Neurologic signs in 58% of neonates
• Histopathology: Characteristic microscopic abnormalities included:
  • Presence of primitive mesenchyme (32%) — immature connective tissue in kidneys
  • Retention of fetal glomeruli (24%) — persistence of immature filtering units
  • Tubular dysplasia (24%) — abnormal development of kidney tubules
• Diagnosis: RD was definitively confirmed by kidney biopsy in one horse; in two additional horses, biopsy suggested RD but necropsy was required for confirmation.

Conclusions and Clinical Relevance

• Renal dysplasia affects a diverse population of horses of various breeds, ages, and sexes, though Paint and Miniature horses are at particularly higher risk.
• The disease can range from no symptoms (subclinical) to severe kidney failure, with neonatal foals being more susceptible to showing clinical illness.
• Because clinical signs can be variable or absent, RD may often go undetected until necropsy unless clinical signs or laboratory abnormalities prompt investigation.
• The study expands understanding of RD in horses, aiding veterinarians in recognizing this congenital condition and considering it in differential diagnoses of kidney disease, especially in affected breeds and young foals.