Plasma Amino Acid and Whole Blood Taurine Concentrations in Cats Eating Commercially Prepared Diets

Plasma amino acid and whole blood taurine concentrations in cats eating commercially prepared diets Cailin R. Heinze, VMD; Jennifer A. Larsen, DVM, PhD; Philip H. Kass, DVM, PhD; Andrea J. Fascetti, VMD, PhD Objective —To establish comprehensive reference ranges for plasma amino acid and whole blood taurine concentrations in healthy adult cats eating commercial diets and to evaluate the relationships of age, sex, body weight, body condition score (BCS), dietary protein concentration, and dietary ingredients with plasma amino acid and whole blood taurine concentrations. Animals —120 healthy adult cats. Procedures —Blood samples and a complete health and diet history were obtained for each cat, and reference intervals for plasma amino acid and whole blood taurine concentrations were determined. Results were analyzed for associations of age, breed, sex, body weight, BCS, use of heparin, sample hemolysis and lipemia, dietary protein concentrations, and dietary ingredients with amino acid concentrations. Results —95% reference intervals were determined for plasma amino acid and whole blood taurine concentrations. A significant difference in amino acid concentrations on the basis of sex was apparent for multiple amino acids. There was no clear relationship between age, BCS, body weight, and dietary protein concentration and amino acid concentrations. Differ - ences in amino acid concentrations were detected for various dietary ingredients, but the relationships were difficult to interpret. Conclusions and Clinical Relevance —This study provided data on plasma amino acid and whole blood taurine concentrations for a large population of adult cats eating commercial diets. Plasma amino acid and whole blood taurine concentrations were not affected by age, BCS, or body weight but were affected by sex and neuter status. Dietary protein concentration and dietary ingredients were not directly associated with plasma amino acid or whole blood taurine concentrations. (Am J Vet Res 2009;70:1374–1382) he past 4 decades have been a time of dramatic ad- ABBREVIATIONS Tvances in knowledge of feline nutrition, especially the relationships between protein metabolism and nu- BCS Body condition score merous disease states. Blood amino acid concentrations NRC National Research Council SSA Sulfosalicylic acid have been used for years to aid in the assessment of nutritional and protein status of cats and have a pivotal role in the diagnosis of specific medical conditions. The ability to measure whole blood and plasma taurine con- eration 1 and dilated cardiomyopathy 2 in cats. These dis- centrations in cats aided in the discovery that taurine coveries have saved many cats from these debilitating deficiency was a major cause of central retinal degen- and potentially fatal diseases. Without the ability to analyze blood amino acid concentrations, these important Received September 12, 2008. connections may never have been made. Amino acid Accepted January 4, 2009. analysis has also been of benefit in investigating many From the Veterinary Medical Teaching Hospital (Heinze), and the other disease processes, including liver disease, 3 diabe- Departments of Molecular Biosciences (Larsen, Fascetti) and Popu- tes mellitus, 4,5 heart disease, 6 and even brain injury, 7 in lation Health and Reproduction (Kass), School of Veterinary Medi- humans and other animals, but comparatively little of cine, University of California-Davis, Davis, CA 95616. Dr. Heinze’s this research has focused on cats. present address is Department of Animal Science, College of Ag- ricultural and Environmental Sciences, University of California- Blood amino acid concentrations are dynamic and Davis, Davis, CA 95616. can be reflective of the most recently consumed diet Supported by grants from the Center for Companion Animal Health, when samples are obtained during the immediate post- School of Veterinary Medicine, University of California-Davis, and prandial period. 8,9 Alternatively, they can reflect the the Morris Animal Foundation and by the Nestlé Purina PetCare mean amino acid concentrations in protein-malnour- Company. Dr. Heinze was supported by an educational grant from ished animals that eat a constant diet, thus allowing de- the Nestlé Purina PetCare Company. 10 The authors thank Dr. Zengshou Yu, Deborah Bee, and Tiffany Chan tection of severe and chronic amino acid deficiencies. for technical assistance. Despite a long history of the use of amino acid con- Address correspondence to Dr. Fascetti ([email protected]). centrations for diagnostic and research purposes, there 1374 AJVR, Vol 70, No. 11, November 2009 are few reports of typical amino acid concentrations in Materials and Methods plasma and whole blood of adult cats eating commercial diets. Although plasma amino acid concentrations for Animals —Blood samples were obtained from 120 adult cats eating commercial diets have been published cats consuming commercially prepared feline diets. All in 2 studies, 6,11 neither of those studies was designed cats were free of apparent systemic illness; obesity was to establish representative reference ranges; therefore, not considered grounds for exclusion. The study popu- data were reported for only small numbers of healthy lation consisted of pet cats belonging to students, fac- cats (29 and 24 cats, respectively) used as control ani- ulty, and staff of the School of Veterinary Medicine at mals in those studies. Additionally, neither study spe- the University of California-Davis, as well as a lesser cifically addressed the diets being fed to the cats. number of university-owned cats housed in 2 separate Currently, published reference values for feline colony facilities. Owners of participating pet cats pro- amino acid concentrations have come primarily from vided written consent for use of their cats in the study. studies 12–15 in which investigators evaluated amino This study was reviewed and approved by the Institu- acid requirements and protein metabolism in growing tional Animal Care and Use Committee of the Univer- kittens consuming purified diets. Those diets were for- sity of California-Davis. mulated with crystalline amino acids or protein con- Development of reference intervals —All owners centrates (such as casein and soy protein), and the bio- were instructed to feed their cats 3 to 5 hours before availability of amino acids in such diets is extremely blood collection because blood amino acid concentra- high. 16,17 In contrast, commercial foods undergo pro- tions are affected by meals and food deprivation. 26 Age, cessing that may negatively impact the bioavailability of sex, neuter status, breed, body weight, BCS (9-point some amino acids, such as lysine, tryptophan, methio- scale), 27 and current health status (detection of vomit- nine, and cysteine. 10,18–20 Additionally, those studies 12–15 ing, diarrhea, sneezing, or coughing or changes in ap- used only small numbers of growing kittens that were petite, body weight, urination, or water intake) were closely related and lacked the genetic diversity inherent recorded at the time of sample collection. One investi- in the general feline population. The potential problem gator (CRH) assigned a BCS to each privately owned cat with the use of data obtained from genetically similar and the cats from one of the university facilities. A staff animals consuming purified diets to develop reference veterinarian assigned the BCS for each cat at the second ranges and nutritional recommendations was addressed university facility. Both of these people used the same in 2006 in the recent version of an NRC publication. 10 criteria 27 to assign each BCS and were experienced with That publication acknowledged the differences be- the technique. Some university-owned cats were fed ad tween diet types and provided nutrient requirement libitum, and samples were obtained at various intervals recommendations based on the availability of nutrients after eating (estimated time ranged from the immediate in ingredients commonly used in foods commercially postprandial period up to 5 hours after eating). available for pets. Our intent in the study reported here was to es- Collection of blood samples —A blood sample (1 to 2 mL) was obtained from each cat with a heparinized or tablish reference ranges for plasma amino acid and unheparinized syringe via jugular or medial saphenous whole blood taurine concentrations in cats. We hy- venipuncture. Heparin supplies were unexpectedly in- pothesized that there would be associations between terrupted because of a major recall 28 during the sample amino acid concentrations and dietary protein con- collection period; thus, heparin was not available for centrations and ingredients. The first objective was all samples (heparin was available at the beginning and to obtain samples from a large number of cats to fa- end but not during the middle of the sample collection cilitate the creation of new reference ranges to more period). Regardless of whether the syringe was hepa- accurately reflect the general feline population. A rinized, all blood samples were immediately transferred second objective was to analyze the collected data to lithium heparin blood tubes; tubes were then gently for relationships between plasma amino acid concen- inverted several times. When r 1.5 mL of blood was trations and signalment, body weight, BCS, dietary collected, 0.5 mL of the sample was placed in a separate protein, and dietary ingredients. Other studies have tube and frozen at –80°C for determination of whole not adequately addressed

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