Comparative Study of Predictive Formulas for Base Excess Estimation of Dry Cat Foods and Their Correlation with Urinary pH
J.T. Jeremias; S.P. Nogueira; M.A. Brunetto; M.O.S. Gomes; E. Teshima; A.C. Carciofi
Food base excess (BE) has a high correlation with cat urinary pH. BE can be calculated utilizing only macroelements or using sulfur amino acids (methionine and cistine). The study compared published formulas to estimate food BE and urinary pH of cats, evaluated the influence of total sulfur and sulfur amino acids on BE calculations, and verified the relationship between food BE with cat blood gases analysis. Nine prepared dry cat foods and nine adults cats were housed in metabolic cages and fed during a 7 days adaptation phase followed by 3 days of total urine collection. Each 24-h of produced urine were pooled by cat and analyzed for density, volume and pH. Food macroelements and amino acids were determined by standards methods. Food BE (mmol/kg DM) was calculated by published formulas in two ways: BE1 with food macroelements (Ca, P, S, Cl, K, Na, and Mg; g/kg DM); BE2 with food macroelements and sulfur amino acids (methionine, and cisteine; g/kg DM). Cat's acid-basic status was studied by blood gas analysis of venous blood. Were collected at 8:00h and 14:00h after 10 days of food adaptation. Urinary pH of cats varied in the interval of 5.83±0.13 (mean±SD) and 7.74±0.12. Food BE1 varied between -291 and 258 mmol/kg DM, and food BE2 between -49 and 377 mmol/kg DM. A mean difference of -195 mmol/kg between EB1 and EB2 was observed. It differences in mean total sulfur content (3.10 g/kg DM) of diets and sulfur occurring in food methionine plus cistine (1.95 g/kg DM). Urine pH has high correlations with food BE1 (pH = 6.76 + 0.0034 BE1+ 0.000001 BE12; r=0.93; p<0.0001) and BE2 (pH = 6.03 + 0.0031 BE2+ 0.000003 BE22; r=0.86; p<0.0001). Other published formulas presented good correlation between BE1 and measured urine pH proposed a direct calculation of macromineral composition and urine pH, without BE estimation, their formula presented a worse correlation in the present study (r=0.71). Some blood gas parameters correlate with food BE measured, including blood pH (r=0.689; p<0.01), bicarbonate concentration (r=0.645; p<0.01) and blood BE (r=0.79; p<0.01). Results confirm that food BE calculation is a useful tool to predict acid-basic balance and urinary pH of cats.