Background Symmetric dimethylarginine (SDMA) has been shown to be an accurate and precise biomarker for calculating estimated glomerular filtration rate (GFR) in humans, as well as a more sensitive biomarker than serum creatinine concentration (sCr) for assessing renal dysfunction. Objectives The purpose of this retrospective study was to report on the utility of measuring serum SDMA concentrations in cats for detection of chronic kidney disease (CKD) before diagnosis by conventional measurement of sCr. Animals Chronic kidney disease cats (n = 21) included those persistently azotemic for ≥3 months (n = 15), nonazotemic cats with GFR >30% decreased from median GFR of normal cats (n = 4), and nonazotemic cats with calcium oxalate kidney stones (n = 2). Healthy geriatric cats (n = 21) were selected from the same colony. Methods Symmetric dimethylarginine concentrations (liquid chromatography‐mass spectroscopy) and sCr (enzymatic colorimetry) were determined retrospectively from historical data or banked serum samples in azotemic cats or at the time GFR (iohexol clearance) was measured in nonazotemic cats. Results Serum SDMA (r = −0.79) and sCr (r = −0.77) concentrations were significantly correlated to GFR (both P < .0001). Symmetric dimethylarginine became increased before sCr in 17/21 cats (mean, 17.0 months; range, 1.5–48 months). Serum SDMA had higher sensitivity (100%) compared with sCr (17%), but lower specificity (91% versus 100%) and positive predictive value (86% versus 100%). Conclusion and Clinical Importance Using serum SDMA as a biomarker for CKD allows earlier detection of CKD in cats compared with sCr, which may be desirable for initiating renoprotective interventions that slow progression of CKD.

The gastrointestinal (GI) microbiome of cats and dogs is increasingly recognized as a metabolically active organ inextricably linked to pet health. Food serves as a substrate for the GI microbiome of cats and dogs and plays a significant role in defining the composition and metabolism of the GI microbiome. The microbiome, in turn, facilitates the host’s nutrient digestion and the production of postbiotics, which are bacterially derived compounds that can influence pet health. Consequently, pet owners have a role in shaping the microbiome of cats and dogs through the food they choose to provide. Yet, a clear understanding of the impact these food choices have on the microbiome, and thus on the overall health of the pet, is lacking. Pet foods are formulated to contain the typical nutritional building blocks of carbohydrates, proteins, and fats, but increasingly include microbiome-targeted ingredients, such as prebiotics and probiotics. Each of these categories, as well as their relative proportions in food, can affect the composition and/or function of the microbiome. Accumulating evidence suggests that dietary components may impact not only GI disease, but also allergies, oral health, weight management, diabetes, and kidney disease through changes in the GI microbiome. Until recently, the focus of microbiome research was to characterize alterations in microbiome composition in disease states, while less research effort has been devoted to understanding how changes in nutrition can influence pet health by modifying the microbiome function. This review summarizes the impact of pet food nutritional components on the composition and function of the microbiome and examines evidence for the role of nutrition in impacting host health through the microbiome in a variety of disease states. Understanding how nutrition can modulate GI microbiome composition and function may reveal new avenues for enhancing the health and resilience of cats and dogs.

We investigated the basis for the reduction in fat pad size in rats fed conjugated linoleic acid (CLA). In the first study, growing female Sprague-Dawley rats (initial weight150 g) were fed diets containing 0, 0.25 and 0.5 g/100 g diet of a purified (97% CLA) and 0.5% of a feed-grade (55% CLA) source of CLA for 5 wk to determine the effects on growth performance and fat mass. There was no effect of CLA on growth rate or food intake. Dietary CLA reduced retroperitoneal fat pad weight 13, 25 and 32% in rats fed 0.25 and 0.5% of the pure CLA and 0.5% of the feed-grade CLA, respectively (P < 0.05). Similar effects were observed in the parametrial fat pad. The reduced pad size was due to smaller adipocyte size rather than a reduced cell number. Relative to the control group, mean cell volume was 15, 28 and 29% lower in tissue from rats fed 0.25 and 0.5% of the pure CLA and 0.5% of the feed-grade CLA, respectively (P < 0.01). In the second study, rats were fed CLA (0 vs. 0.5%) for 7 or 49 d. Reductions in fat pad weight were observed within 7 d. In addition, the effects of CLA on energy metabolism were studied in the chronically fed rats. There were no significant effects of CLA on oxygen consumption, CO₂ or heat production. During wk 4 of feeding, but not at other times, there was a 5% lower respiratory quotient in CLA-fed rats (P < 0.05). There was a time-dependent accumulation of CLA in adipose tissue and a decrease in monounsaturated fatty acids. These results suggest that the reduction in fat mass in rats fed CLA can be accounted for by a reduction in cell size rather than a change in cell number.

Background: Symmetric 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. Hypothesis: Differences in lean body mass (LBM) influence sCr, but not serum SDMA concentrations. Animals: Forty-one healthy Beagles, mean age 9.9 years (range: 3.1–14.8 years), were studied over a 6 month period. Methods: Serum 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 (R2 = 0.38), but not SDMA concentration. Time on food was the only significant explanatory variable for SDMA concentration (R2 = 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.

Background Serum concentrations of symmetric dimethylarginine (SDMA) detected chronic kidney disease (CKD) in cats an average of 17.0 months before serum creatinine (Cr) concentrations increased above the reference interval. Objectives To report on the utility of measuring serum SDMA concentrations in dogs for detection of CKD before diagnosis by measurement of serum Cr. Animals CKD dogs (n = 19) included those persistently azotemic for ≥3 months (n = 5), dogs that were azotemic at the time of death (n = 4), and nonazotemic dogs (n = 10). CKD dogs were compared with healthy control dogs (n = 20). Methods Retrospective study, whereby serum Cr concentrations were determined by enzymatic colorimetry and serum SDMA concentrations were determined by liquid chromatography‐mass spectrometry in dogs with necropsy confirmed CKD. Results Serum SDMA increased before serum Cr in 17 of 19 dogs (mean, 9.8 months; range, 2.2–27.0 months). Duration of elevations in serum SDMA concentrations before the dog developed azotemia (N = 1) or before the dog died (N = 1) was not determined. Serum SDMA and Cr concentrations were linearly related (r = 0.84; P < .001). Serum SDMA (r = −0.80) and serum Cr (r = −0.89) concentrations were significantly related to glomerular filtration rate (both P < .001). Conclusion and Clinical Importance Using serum SDMA as a biomarker for CKD allows earlier detection of kidney dysfunction in dogs than does measurement of serum Cr. Earlier detection might be desirable for initiating renoprotective interventions that slow progression of kidney disease.

Objective—To evaluate the effects of a food supplemented with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. Design—Randomized, double-blinded, controlled clinical trial. Animals—38 client-owned dogs with osteoarthritis examined at 2 university veterinary clinics. Procedures—Dogs were randomly assigned to receive a typical commercial food (n = 16) or a test food (22) containing 3.5% fish oil omega-3 fatty acids. On day 0 (before the trial began) and days 45 and 90 after the trial began, investigators conducted orthopedic evaluations and force-plate analyses of the most severely affected limb of each dog, and owners completed questionnaires to characterize their dogs' arthritis signs. Results—The change in mean peak vertical force between days 90 and 0 was significant for the test-food group (5.6%) but not for the control-food group (0.4%). Improvement in peak vertical force values was evident in 82% of the dogs in the test-food group, compared with 38% of the dogs in the control-food group. In addition, according to investigators' subjective evaluations, dogs fed the test food had significant improvements in lameness and weight bearing on day 90, compared with measurements obtained on day 0. Conclusions and Clinical Relevance—At least in the short term, dietary supplementation with fish oil omega-3 fatty acids resulted in an improvement in weight bearing in dogs with osteoarthritis.