Androgen-dependent cystinuria: why castrate
3-year-old intact male Mastiff with a second episode of cystine uroliths within 8 months, confirmed by quantitative analysis. Urinalysis shows hexagonal crystals and pH 6.0.
Which preventive measure has the greatest impact in this dog?
chevron_right Show answer and explanation
A. Castration
Correct. In breeds with type III (androgen-dependent) cystinuria, such as Mastiff, Scottish Deerhound or Irish Terrier, castration markedly reduces cystine excretion and recurrence, often without chronic medication.
B. An acidifying diet to keep urine pH low
Cystine is more soluble in alkaline urine; acidification promotes its precipitation.
C. A high-protein diet to compensate for amino acid loss
More protein (and methionine) increases cystinuria. The preventive diet is protein-reduced, alkalinising and moist.
D. Long-term allopurinol
Allopurinol acts on purine (urate) metabolism, not on the tubular amino acid reabsorption defect that causes cystinuria.
lightbulb Key takeaway
Cystinuria is a tubular reabsorption defect of cystine and other dibasic amino acids, almost exclusive to males in the androgen-dependent forms. Castrate affected males of these breeds and do not use them for breeding.
References: Lulich JP et al. ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats (2016)
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.