The global prevalence of cystine urolithiasis in dogs is approximately 1%, although this varies considerably from country to country. The aim of this investigation was to determine the relative frequency of cystine urolithiasis in canine patients in the compared to other forms of urolithiasis, and identify breeds particularly affected. The study also looked at age, sex and neutering status, to see if these factors also have an effect on the risk for development of cystine calculi.

All canine uroliths submitted to Hills Pet Nutrition, for quantitative analysis by the Minnesota Urolith Centre, from January 2000 until December 2006 were included in the study. Chi-square tests were used to test whether breed, gender or reproductive status were different in dogs with cystine stones compared with all dogs with urolithiasis.

A total of 11027 calculi were analysed, of which 348 (3.2%) were composed of cystine. Affected dogs were of 39 different breeds; additionally 60 dogs were of mixed or unknown breeding. Breeds found to be significantly affected by cystine urolithiasis were the Bassett Hound, Bulldog, Bull Mastiff, Deerhound,

Irish Terrier, Mastiff, Newfoundland, Rottweiler, Staffordshire Bull Terrier and Whippet. The study found males were significantly over-represented with only one case occurring in a female. Within the population of affected males, 41 were castrated and 275 entire; there were significantly more entire dogs with cystine calculi than uroliths of other types (P<0.0001). The average age at which cystine urolithiasis occurs was found to be 73 months, with 63% of cases occurring between 37-96 months.

This study showed that the relative incidence of cystine urolithiasis in the United Kingdom is significantly greater than that documented in the United States. Of particular interest was the observation that the Staffordshire Bull Terrier, which had not been shown to be significantly affected by cystine calculi in any other investigation of this type, made up 21.6% of cystine cases (73 uroliths) in this study. Although there is no substitute for definitive urolith analysis, this investigation indicates where a clinician should have an increased suspicion of cystine calculi in a canine urolithiasis patient.