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

Renal dysplasia (RD) is a congenital malformation with variable clinical expression and limited characterization in horses.

We hypothesized that RD occurs in horses across a broad age range and may be overrepresented in specific breeds. Our objective was to describe clinical, clinicopathologic, and histopathologic findings in horses with RD.

Twenty-five horses with RD identified from a veterinary teaching hospital between 1991 and 2021. Horses included neonates, young horses, and adults, with ages ranging from 0 days to 24 years and representing multiple breeds and both sexes.

Retrospective case series including review of laboratory data, ultrasonographic findings, treatment, outcome, and histopathology. Breed prevalence was assessed using Fisher's exact test. Outcomes included age and breed distribution, clinical and laboratory abnormalities, and diagnostic findings associated with RD.

Renal dysplasia was bilateral in 84% of cases and diffuse in 68%. Eleven horses (44%) had RD as an incidental necropsy finding. Clinical signs were more common in neonates, with azotemia in 64% and hyponatremia in 37%. Neurologic signs were reported in 58% of neonates. Paint horses (odds ratio [OR]: 21.3; 95% CI, 8.0-56.7) and Miniature horses (OR: 12.9; 95% CI, 4.4-37.7) were overrepresented compared with all other breeds combined (P < .0001). Histopathologic findings included primitive mesenchyme (32%), retention of fetal glomeruli (24%), and tubular dysplasia (24%). RD was confirmed by biopsy in one horse; in 2 others, biopsy findings were suggestive but not definitive, requiring necropsy confirmation.

Renal dysplasia affects a variety of breeds and ages of horses, including both sexes. Paint horses and Miniature horses were overrepresented. Renal dysplasia ranges from subclinical to causing severe kidney disease. Affected neonatal foals are more likely to have clinical signs.