BackgroundSymmetric dimethylarginine (SDMA) is an accurate and precise biomarker for estimating glomerular filtration rate (GFR) in humans and cats. Serum creatinine (sCr) also correlates with GFR, but has limitations as a biomarker of renal function because nonrenal factors can influence its concentration.HypothesisDifferences in lean body mass (LBM) influence sCr, but not serum SDMA concentrations.AnimalsForty‐one healthy Beagles, mean age 9.9 years (range: 3.1–14.8 years), were studied over a 6 month period.MethodsSerum biomarkers of renal function were measured prospectively at baseline, and 1, 3, and 6 months. SDMA concentrations were measured by liquid chromatography‐mass spectroscopy and sCr concentrations by enzymatic colorimetry. Body composition was determined by dual energy x‐ray absorptiometry.Results LBM (P < .001) and age (P = .006) were significant explanatory variables for sCr concentration (R 2  = 0.38), but not SDMA concentration. Time on food was the only significant explanatory variable for SDMA concentration (R 2  = 0.49). SDMA concentrations decreased across time (P < .001). LBM was affected by sex (males > females; P = .02). Mature adult dogs (<8 years) had greater LBM compared with geriatric dogs (≥8 years; P < .001).Conclusion and Clinical Importance sCr concentrations, but not SDMA concentrations, are influenced by LBM, which limits sCr utility as a biomarker for monitoring renal function in dogs with decreased LBM. Reductions in LBM can lower sCr concentration and overestimate GFR. SDMA concentrations, but not sCr concentrations were influenced by time on food. SDMA could have clinical advantages over sCr in monitoring response to nutritional interventions.

Because animal studies are labor intensive, predictive equations are used extensively for calculating metabolizable energy (ME) concentrations of dog and cat pet foods. The objective of this retrospective review of digestibility studies, which were conducted over a 7-year period and based upon Association of American Feed Control Officials (AAFCO) feeding protocols, was to compare the accuracy and precision of equations developed from these animal feeding studies to commonly used predictive equations. Feeding studies in dogs and cats (331 and 227 studies, respectively) showed that equations using modified Atwater factors accurately predict ME concentrations in dog and cat pet foods (r2 = 0.97 and 0.98, respectively). The National Research Council (NRC) equations also accurately predicted ME concentrations in pet foods (r2 = 0.97 for dog and cat foods). For dogs, these equations resulted in an average estimate of ME within 0.16% and 2.24% of the actual ME measured (equations using modified Atwater factors and NRC equations, respectively); for cats these equations resulted in an average estimate of ME within 1.57% and 1.80% of the actual ME measured. However, better predictions of dietary ME in dog and cat pet foods were achieved using equations based on analysis of gross energy (GE) and new factors for moisture, protein, fat and fiber. When this was done there was less than 0.01% difference between the measured ME and the average predicted ME (r2 = 0.99 and 1.00 in dogs and cats, respectively) whereas the absolute value of the difference between measured and predicted was reduced by approximately 50% in dogs and 60% in cats. Stool quality, which was measured by stool score, was influenced positively when dietary protein digestibility was high and fiber digestibility was low. In conclusion, using GE improves predictive equations for ME content of dog and cat pet foods. Nondigestible protein and fiber content of diets predicts stool quality.

A miniature schnauzer presented for evaluation of a persistent lower urinary tract obstruction. Further examination revealed that the dog had developed an obstructive, inflammatory polyp secondary to a long-standing urinary tract infection. The polyp was located within the proximal urethra and interfered with normal voiding. The polyp was visualized using flexible endoscopy and then was successfully ablated using the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser. The Nd:YAG laser is a potentially useful tool for treating various lesions of the lower urinary tract.

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