Starch to protein ratio and food moisture content influence water balance and urine supersaturation in cats

by Maria Eduarda Gonçalves Tozato, Stephanie de Souza Theodoro, Leticia Warde Luis, Lucas Bassi Scarpim, Pablo da Cunha Costa, Ana Paula Judice Maria, Gener Tadeu Pereira, Aulus Cavalieri Carciofi

Two starch to protein ratios (high starch [HS], 25% starch and 36% protein; high protein [HP], 15% starch and 53% protein on DM basis) and two moisture contents (5%, dry kibbles; 80%, wet food) were compared in a 2 x 2 factorial arrangement totaling 4 diets. Each diet was evaluated in 9 cats, with 8 d of total collection of urine and feces. Results were subjected to an analysis of variance of the effects of starch to protein ratio, moisture content and their interactions (P<0.05). Urine density was lower and volume was higher in cats fed wet foods (P<0.01). Calcium (Ca) urine concentration was higher for dry and HP diets (P<0.05). The oxalate urine concentration was 60% higher for cats fed both HS formulations (dry and wet; P<0.05). The relative supersaturation (RSS) of urine for calcium oxalate was higher for dry foods and HS formulations (P<0.01), and for struvite, it was lower for both wet foods, and among the dry diets, it was lower for the HS than for the HP formulation (P<0.01). Foods with a high protein-to-starch ratio reduced urine oxalate and RSS for calcium oxalate in wet and dry diets, and wet foods reduced RSS for calcium oxalate and struvite.