Relative supersaturation (RSS) measures the risk for crystal formation or dissolution in urine, and has been validated in dogs and cats (Roberston et al. 2002). In cats, struvite RSS < 1 predicts dissolution in vitro (Houston et al. 2011).
The aim of this study was to assess whether sterile canine urine with struvite RSS < 1 leads to in vitro struvite dissolution.
Six healthy adult dogs were fed a dry expanded diet (Royal Canin S/O-Kcal-Control dog) for 10 days: 7 days of adaptation and 3 days of urine collection. The urines of the 6 dogs were pooled: urine pH and concentrations of 10 solutes (Ca2+, Mg2+, Na+, K+, NH4+, phosphate, citrate, sulphate, oxalate and uric acid) were measured to calculate RSS with the software SupersatTM. Urine was distributed into bottles stored at -20°C until dissolution test.
A canine urolith analysed at 100% struvite was immersed on day 0 in a bottle of urine and put in a stove at 38°C under stirring. Twenty-four hours later, the urines were filtered to collect the stone, which was dried and weighed. Every day until running out of urine (25 days), the stone was placed in a new bottle and the procedure restarted to follow the dissolution of the stone.
For each dog and for the pool of urine, the struvite RSS were < 1.
After 25 days, 60% of the struvite had dissolved (Figure 1).
Kinetic of canine struvite stone dissolution in urine with struvite RSS < 1.
A sterile dog urine with struvite RSS < 1 is effective at dissolving struvite uroliths.