scholarly journals Minimum dietary methionine requirements in Miniature Dachshund, Beagle, and Labrador Retriever adult dogs using the indicator amino acid oxidation technique

2020 ◽  
Vol 98 (11) ◽  
Author(s):  
Wilfredo D Mansilla ◽  
James R Templeman ◽  
Lisa Fortener ◽  
Anna K Shoveller
Keyword(s):  
Amino Acid ◽  
National Research Council ◽  
Basal Diet ◽  
Acid Oxidation ◽  
Total Production ◽  
Two Phase ◽  
Minimum Requirement ◽  
Linear Mixed Effects ◽  
Low Protein ◽  
Labrador Retrievers

Abstract The objective of this study was to determine the minimum requirement (MR) for methionine (Met), when cyst(e)ine (Cys) is provided in excess, in adult dogs of three different breed sizes using the indicator amino acid (AA) oxidation (IAAO) technique. In total, 12 adult dogs were used: 1 neutered and 3 spayed Miniature Dachshunds (4.8 ± 0.4 kg body weight [BW], mean ± SD), 4 spayed Beagles (9.5 ± 0.7 kg BW, mean ± SD), and 4 neutered Labrador Retrievers (31.8 ± 1.7 kg BW, mean ± SD). A deficient Met basal diet with excess Cys was formulated. Dogs were fed the basal diet randomly supplemented with different Met-Alanine (Ala) solutions to achieve final Met concentrations in experimental diets of 0.21%, 0.26%, 0.31%, 0.36%, 0.41%, 0.46%, and 0.66% (as-fed basis). After 2 d of adaptation to the experimental diets, dogs underwent individual IAAO studies. During the IAAO study day, the total feed was divided into 13 equal meals; at the sixth meal, dogs were fed a bolus of l-[1-13C]-phenylalanine (Phe), and thereafter, l-[1-13C]-Phe was supplied with every meal. The total production of 13CO2 during isotopic steady state was determined by the enrichment of 13CO2 in breath samples, and the total production of CO2 measured using indirect calorimetry. The mean MR for Met and the upper 95% confidence limit (CL) were determined using a two-phase linear mixed-effects regression model. For Miniature Dachshunds, the MR for Met was between the first two dietary Met concentrations and is, therefore, between 35.7 and 44.1 mg.kg BW−1·d−1 (0.21% to 0.26%, as-fed basis; no requirement could be determined on a metabolic BW basis). For Beagles and Labrador Retrievers, the MR for Met was 57.5 and 50.4 mg.kg BW−1·d−1, 107.7 and 121.8 mg/kg BW^0.75, or 0.338 and 0.360%, respectively (as-fed basis). The upper 95% CL of Met requirements was 77.9 and 72.4 mg.kg BW−1·d−1, 147.8 and 159.6 mg/kg BW^0.75,or 0.458 and 0.517% for Beagles, and Labradors, respectively (as-fed basis). When pooling data from Beagles and Labrador Retrievers, the MR and upper 95% CL were 56.0 and 75.8 mg.kg BW−1·d−1 or 118.4 and 150.5 mg/kg BW^0.75 or 0.360% and 0.482% (as-fed basis). In conclusion, the MR and the upper 95% CL for Met are different for Dachshunds when compared with Beagles and Labrador Retrievers. Using this low-protein diet, the estimated upper 95% CL Met requirement for Beagles and Labrador is higher than those recommended in the National Research Council (NRC), but NRC is similar to the estimated upper 95% CL for Dachshunds.

scholarly journals Adult dogs of different breed sizes have similar threonine requirements as determined by the indicator amino acid oxidation technique

2020 ◽  
Vol 98 (3) ◽  
Author(s):  
Wilfredo D Mansilla ◽  
Lisa Fortener ◽  
James R Templeman ◽  
Anna K Shoveller
Keyword(s):  
Amino Acid ◽  
Basal Diet ◽  
Acid Oxidation ◽  
Total Production ◽  
Experimental Diet ◽  
Two Phase ◽  
Deficient Diet ◽  
Amino Acid Oxidation ◽  
The Mean ◽  
Labrador Retrievers

Abstract Threonine (Thr) requirements for immature (growing) Beagles have been determined, but little knowledge is available on Thr requirements for maintenance in mature dogs. Moreover, differences of Thr requirements among different breeds or sizes of adult dogs have not been investigated. The objective of the present study was to determine Thr requirements in adult dogs of three different breeds using the indicator amino acid oxidation (IAAO) technique. In total, 13 adult dogs were used, 4 Miniature Dachshunds (5.8 ± 0.4 kg body weight [BW]; 3 spayed and 1 neutered), 4 spayed Beagles (9.3 ± 0.6 kg BW), and 5 neutered Labrador Retrievers (30.5 ± 1.7 kg BW). Dogs were fed a Thr-deficient diet (Thr = 0.23%) and randomly allocated to receiving one of seven concentrations of Thr supplementation (final Thr concentration in experimental diets was 0.23%, 0.33%, 0.43%, 0.53%, 0.63%, 0.73%, and 0.83%; as fed basis) for 2 d. After 2 d of adaptation to the experimental diets, dogs underwent individual IAAO studies. During the IAAO studies, total daily feed was divided into 13 equal meals; at the sixth meal, dogs were fed a bolus of l-[1-13C]-Phenylalanine (Phe) (9.40 mg/kg BW), and thereafter, l-[1-13C]-Phe (2.4 mg/kg BW) was supplied with every meal. Before feeding the next experimental diet, dogs were fed a Thr-adequate basal diet for 4 d (Thr = 0.80% as fed basis) in known amounts that maintained individual dog BW. Total production of 13CO2 during isotopic steady state was determined by enrichment of 13CO2 in breath samples and total production of CO2 measured using indirect calorimetry. The mean requirements for Thr, defined as the breakpoint, and the 95% confidence interval (CI) were determined using a two-phase linear regression model. For Miniature Dachshunds, the two-phase model was not significant, and Thr requirements could not be determined. Mean Thr requirements for Beagles and Labradors were 72.2 and 64.1 mg/kg BW on an as-fed basis, respectively. The requirement for Thr between these two dog breeds was not different (P > 0.10). Thus, the data for Beagles and Labradors were pooled and a mean requirement for Thr was determined at 66.9 mg/kg BW, and the 95% CI was estimated at 84.3 mg/kg BW. In conclusion, estimated Thr requirements for Beagles and Labradors did not differ, and these recommendations are higher than those suggested by NRC (2006) and AAFCO (2014) for adult dogs at maintenance.

scholarly journals Lysine requirements in small, medium, and large breed adult dogs using the indicator amino acid oxidation technique1

2020 ◽  
Vol 4 (3) ◽  
Author(s):  
Katja A K Sutherland ◽  
Wilfredo D Mansilla ◽  
Lisa Fortener ◽  
Anna K Shoveller
Keyword(s):  
Amino Acid ◽  
Feed Intake ◽  
Dry Matter ◽  
National Research Council ◽  
Acid Oxidation ◽  
Total Production ◽  
Test Diet ◽  
Two Phase ◽  
Amino Acid Oxidation ◽  
Matter Basis

Abstract There is a lack of knowledge regarding the lysine (Lys) requirements of mature dogs and whether there are breed differences. The present study aimed to determine the Lys requirement in three breeds of mature dogs using the indicator amino acid oxidation (IAAO) technique. Thirteen adult dogs were used, four Miniature Dachshunds (5.39 ± 0.71 kg; 1.05 ± 0.02 yr old, mean ± SD), four Beagles (8.09 ± 0.40 kg; 5.03 ± 0.09 yr old, mean ± SD), and five Labrador Retrievers (29.42 ± 2.04 kg; 3.30 ± 0.69 yr old, mean ± SD). After 14 d of adaptation to a basal extruded kibble diet, dogs were fed a test diet mildly deficient in Lys (Lys concentration = 0.36%) at 17 (Miniature Dachshunds) or 13 g/kg body weight (BW; Beagles and Labradors) for 2 d. The test diet was supplemented with one of seven isonitrogenous Lys–Ala solutions, resulting in a final dietary Lys concentration of 0.36%, 0.40%, 0.44%, 0.50%, 0.54%, 0.58%, and 0.62% (as-fed basis). Dogs received dietary concentrations of Lys in random order and no dog received the same order. Following 2 d of adaptation to the experimental diets, the dogs underwent IAAO studies. During the IAAO studies, total daily feed was divided in 13 equal meals. At the sixth meal, dogs were fed a bolus of L-[1-13C]-Phe (9.40 mg/kg BW); thereafter, L-[1-13C]-Phe was supplied with every meal (2.4 mg/kg BW). Total production of 13CO2 (F13CO2) during isotopic steady state was determined by enrichment of 13CO2 of breath samples and total production of CO2, measured using indirect calorimetry. A two-phase linear regression model was used to derive the mean Lys requirement, defined as the breakpoint, and the upper 95% confidence limit was calculated as the recommended allowance (RA) for Lys intake. For Miniature Dachshunds, the study was repeated with a feed intake of 14 g/kg BW, but Lys requirements could not be determined at either feed intake, suggesting a requirement below the lowest concentration and intake. Mean Lys requirements for Beagles and Labradors were 0.455% (59.16 mg/kg BW) and 0.440% (57.19 mg/kg BW), respectively, on a dry matter basis. Pooling the data for these breeds provides a mean estimate of the Lys requirement at 0.448% (58.21 mg/kg BW) with an upper 95% CL of 0.526% (68.41 mg/kg BW) on a dry matter basis. In conclusion, the Lys requirements of Beagles and Labradors are similar, while the requirement for Miniature Dachshunds is undetermined and likely lower. The estimated Lys requirement for Beagles and Labradors is higher than the National Research Council recommendation.

scholarly journals Tryptophan requirements in small, medium, and large breed adult dogs using the indicator amino acid oxidation technique1

2019 ◽  
Vol 97 (8) ◽  
pp. 3274-3285 ◽  
Author(s):  
James R Templeman ◽  
Wilfredo D Mansilla ◽  
Lisa Fortener ◽  
Anna K Shoveller
Keyword(s):  
Amino Acid ◽  
Dry Matter ◽  
Basal Diet ◽  
Acid Oxidation ◽  
Total Production ◽  
Deficient Diet ◽  
Study Objective ◽  
Amino Acid Oxidation ◽  
Indispensable Amino Acid ◽  
Labrador Retrievers

Abstract Tryptophan (Trp) is an indispensable amino acid (AA) for dogs of all life stages; however, although Trp requirements for growing dogs are derived from 3 dose–response studies, there are no empirical data on Trp requirements for adult dogs at maintenance. The study objective was to determine Trp requirements of adult dogs of 3 different breeds using the indicator amino acid oxidation (IAAO) technique. Four spayed or neutered Miniature Dachshunds (5.28 ± 0.29 kg BW), 4 spayed Beagles (9.32 ± 0.41 kg BW), and 5 neutered Labrador Retrievers (30.51 ± 2.09 kg BW) were used. After a 14-d adaptation to a Trp-adequate basal diet (Trp = 0.482% dry matter), all dogs were fed a mildly Trp-deficient diet for 2 d (Trp = 0.092% dry matter) before being randomly allocated to receiving 1 of 7 concentrations of Trp supplementation (final Trp content in experimental diets was 0.092, 0.126, 0.148, 0.182, 0.216, 0.249, and 0.283% dry matter) and all dogs received all Trp treatments. After 2-d adaptation to the experimental diets, dogs underwent individual IAAO studies. Total feed was divided in 13 equal meals; at the sixth meal, dogs were fed a bolus of L-[1-13C]-Phenylalanine (Phe) (9.40 mg/kg BW), and thereafter, L-[1-13C]-Phe was supplied (2.4 mg/kg BW) with every meal. Total production of 13CO2 during isotopic steady state was determined by enrichment of 13CO2 in breath samples and total production of CO2 measured using indirect calorimetry. The maintenance requirement for Trp and the 95% confidence interval (CI) were determined using a 2-phase linear regression model. Mean Trp requirements were estimated at 0.154, 0.218, and 0.157% (dry-matter) for Dachshunds, Beagles, and Labradors, respectively. The upper 95% CI were 0.187, 0.269, and 0.204% (dry-matter) for Dachshunds, Beagles, and Labradors. In conclusion, estimated Trp requirements are higher for Beagles compared with Labradors or Dachshunds, and all estimated requirements are higher than those currently recommended by the NRC and AAFCO.

scholarly journals PSXI-31 Program Chair Poster Pick: Determination of the threonine requirement in adult and senior Labrador Retrievers using the indicator amino acid oxidation technique

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 321-322
Author(s):  
Jordan T Weil ◽  
Jessica L Varney ◽  
Jason W Fowler ◽  
Craig N Coon
Keyword(s):  
Amino Acid ◽  
Control Diet ◽  
Genetic Selection ◽  
Isotope Ratio Mass Spectrometry ◽  
Acid Oxidation ◽  
Amino Acid Oxidation ◽  
Amino Acid Requirements ◽  
Indispensable Amino Acids ◽  
Nutrient Profiles ◽  
Labrador Retrievers

Abstract Although nutrient profiles for canines have been developed in the past, the need to update amino acid (AA) requirements has gained importance as genetic selection changes the recommended nutrients. Correctly feeding AA to canines can have enormous effects, considering a deficiency or excess of such nutrient can lead to weight loss, disease, or in some cases, death. Amino acid requirements can be determined through the nitrogen balance or indicator amino acid oxidation (IAAO) methods. In this experiment, the IAAO technique was used to determine the threonine (Thr) requirement in Labrador retrievers. A total of six dogs (6 adult and 6 senior) were subjected to six diets with varying levels of Thr, ranging from deficient to excess. Diets were formulated to 1.6x NRC values for all indispensable amino acids. The control diet was fed for two days, followed by a day in which the test diet was fed, a tracer AA was supplied, and breath samples were collected. On test day, a priming dose of L-[1-13C]phenylalanine (Cambridge Isotope Laboratories, Inc.) based on the subject’s body weight was first supplied, followed by [1-13C]Phe doses every thirty minutes, spanning a four hour period. A respiration mask was placed on each subject every thirty minutes (Oxymax, Columbus Instruments), 13CO2 was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a piecewise model of best fit (JMP® Pro 15). The segmented line regression showed that the Thr mean and population requirements were determined to be 1.21 ± 0.24 and 0.92 ± 0.17 g/1000kcal (mean ± 2SD) for adult and senior dogs, respectively. As the pet food industry becomes more specialized in diets relating to aging, and diseased canines, updating the amino acid requirements related to such animals is increasingly important.

scholarly journals Phenylalanine requirement in children with classical PKU determined by indicator amino acid oxidation

2002 ◽  
Vol 283 (6) ◽  
pp. E1249-E1256 ◽  
Author(s):  
Glenda Courtney-Martin ◽  
Rachelle Bross ◽  
Mahroukh Raffi ◽  
Joe T. R. Clarke ◽  
Ronald O. Ball ◽  
...  
Keyword(s):  
Amino Acid ◽  
Acid Oxidation ◽  
Phenylalanine Concentration ◽  
Two Phase ◽  
Amino Acid Oxidation ◽  
Blood Phenylalanine ◽  
Plasma Phenylalanine ◽  
Crossover Analysis ◽  
The Mean ◽  
The Difference

Dietary restriction of phenylalanine is the main treatment for phenylketonuria (PKU), and current estimates of requirements are based on plasma phenylalanine concentration and growth. The present study aimed to determine more precisely the phenylalanine requirements in patients with the disease by use of indicator amino acid oxidation, withl-[1-13C]lysine as the indicator. Breath13CO2 production (F13 co 2) was used as the end point. Finger-prick blood samples were also collected for measurement of phenylalanine to relate phenylalanine intake to blood phenylalanine levels. The mean phenylalanine requirement, estimated using a two-phase linear regression crossover analysis, was 14 mg · kg−1 · day−1, and the safe population intake (upper 95% confidence interval of the mean) was found to be 19.5 mg · kg−1 · day−1. A balance between phenylalanine intake and the difference between fed and fasted blood phenylalanine concentration was observed at an intake of 20 mg · kg−1 · day−1. The similarity between these two values (19.5 and 20 mg · kg−1 · day−1) suggests that the maximal phenylalanine intake for children with PKU should be no higher than 20 mg · kg−1 · day−1.

scholarly journals Adaptation to low-protein diets in renal failure: leucine turnover and nitrogen balance.

1990 ◽  
Vol 1 (1) ◽  
pp. 66-75
Author(s):  
T H Goodship ◽  
W E Mitch ◽  
R A Hoerr ◽  
D A Wagner ◽  
T I Steinman ◽  
...  
Keyword(s):  
Renal Failure ◽  
Amino Acid ◽  
Protein Degradation ◽  
Nitrogen Balance ◽  
Acid Oxidation ◽  
Leucine Incorporation ◽  
Adaptive Responses ◽  
Protein Balance ◽  
Amino Acid Oxidation ◽  
Low Protein

In normal subjects, short to intermediate responses to dietary protein restriction include decreased amino acid oxidation and protein degradation plus increased utilization of amino acids for protein synthesis; these responses are activated to improve amino acid utilization and nitrogen balance. To assess whether chronic renal failure (CRF) impairs the adaptive responses to a low-protein diet, we measured nitrogen balance and the kinetics of infused L-(15N,1-13C)leucine during fasting and feeding. In six adult CRF and four control (C) subjects, 0.6 (LP) and 1.0 (HP) g protein kg-1 day-1 diets were compared. LP reduced feeding stimulated oxidation of leucine by 26% in CRF and 33% in C (P = NS). During fasting, oxidation was unaffected by diet or CRF. For both groups, feeding suppressed protein degradation to the same extent; leucine incorporation into protein did not change. Nitrogen balance during the two diets was the same with C and CRF, as was protein balance estimated from results of measured leucine kinetics. Thus, patients with CRF can activate appropriate adaptive responses to LP inasmuch as reduced amino acid oxidation occurring with feeding and estimates of protein balance did not differ from control.

PSX-A-17 Late-Breaking: Methionine and total sulfur amino acid requirements for pups (>14 wk to 9 months), adults, and senior Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

2021 ◽  
Vol 99 (Supplement_3) ◽  
pp. 374-374
Author(s):  
Jessica L Varney ◽  
Charlene Watson ◽  
Nicole Colopy ◽  
John Moss ◽  
Jordan T Weil ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Control Diet ◽  
Age Groups ◽  
Isotope Ratio Mass Spectrometry ◽  
Co2 Production ◽  
Acid Oxidation ◽  
Total Sulfur ◽  
Amino Acid Oxidation ◽  
Labrador Retrievers

Abstract Methionine and cystine are often considered limiting amino acids in canine diets but limited requirement studies have been conducted especially for different life stages. Eighteen Labrador Retrievers (6 pups (>14 wk-9 month), 6 adults, and 6 seniors [>8yr)] were utilized in feeding studies to evaluate the changing requirements of methionine (Met) and total sulfur amino acids (TSAA) as canines age. For this study, the indicator amino acid oxidation (IAAO) technique was utilized to determine the amino acid (AA) requirements in each of the three age groups. Dogs were subjected to diets ranging from deficient to excess, with indispensable amino acids formulated at 1.6x NRC values. To allow for adaptation, a control diet with same dietary ingredients, protein and amino acid levels was fed for two days prior to feeding the test diets on the third day. On test day, a baseline breath sample was collected for determining CO2 production using a respiration mask (Oxymax, Columbus Instruments). A priming dose of L-[1-13C] phenylalanine (Cambridge Isotope Laboratories, Inc.) based on body weight was utilized, followed by [1-13C] Phe doses every 30 minutes, spanning a four hour period. After each dose 13CO2 was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a piecewise model of best fit (JMP® Pro 16). A segmented line regression showed Met and TSAA mean and population requirements for pups (>14 wk-9 mo.) were 0.78 ± 0.16 and 1.53 ± 0.21 g/1000kcal (mean ± 2SD), respectively. Meanwhile, for adults, mean and population requirements for Met and TSAA were estimated to be 0.68 ± 0.19 and 1.4 ± 0.30 g/1000kcal (mean ± 2SD), respectively, and for seniors, Met and TSAA mean and population requirements were determined to be 0.62 ± 0.17 and 1.27 ± 0.23 g/1000kcal (mean ± 2SD), respectively.

scholarly journals Dietary Phenylalanine and Tyrosine Requirements in Healthy Human Pregnancy

2020 ◽  
Vol 4 (Supplement_2) ◽  
pp. 978-978
Author(s):  
Madeleine Ennis ◽  
Kenneth Lim ◽  
Ronald Ball ◽  
Paul Pencharz ◽  
Glenda Courtney-Martin ◽  
...  
Keyword(s):  
Amino Acid ◽  
Life Stage ◽  
Experimental Studies ◽  
Late Pregnancy ◽  
Acid Oxidation ◽  
Current Recommendation ◽  
Two Phase ◽  
Healthy Human ◽  
Dietary Requirement ◽  
Indispensable Amino Acid

Abstract Objectives Phenylalanine (PHE), an indispensable amino acid, is required for protein synthesis and is fundamental for proper fetal development. PHE is the precursor for tyrosine (TYR), a conditionally indispensable amino acid that is crucial for synthesis of dopamine, norepinephrine and epinephrine. The current recommendation for PHE + TYR during pregnancy is 36 mg/kg/d, which is factorially determined and not based on experimental studies. Our objective was to experimentally determine PHE + TYR requirements during early (13–19 wks) and late (33–39 wks) gestation, accounting for potential changes in requirement since metabolism and rate of growth are not static throughout pregnancy. Methods 20 women (22–39 y) were studied using the non-invasive stable isotope based indicator amino acid oxidation technique (with L-[1–,13C]Leucine as indicator) for a total of 51 study days. A range of PHE intakes (5 to 100 mg/kg/d) were provided in early and late pregnancy as isonitrogenous and isocaloric meals on separate study days, in the absence of dietary tyrosine. Breath samples were collected at baseline and isotopic steady state. Samples were analyzed for ,13C enrichment on an Isotope Ratio Mass Spectrometer, and the PHE + TYR requirement was determined using two-phase linear regression crossover analysis to identify a breakpoint in ,13CO2 production (represents the minimum dietary requirement) in response to changes in PHE intake. Results Results suggest the PHE + TYR requirement is 43 and 55 mg/kg/d in early and late pregnancy respectively. Conclusions Our preliminary results suggest that PHE + TYR requirements in pregnancy are higher compared to current recommendations, and are different between gestational stages. These results are similar to our previous findings of increased requirements for dietary protein, lysine and PHE (in the presence of excess TYR) in late compared to early pregnancy. They also highlight the need to investigate the dietary requirement of the remaining indispensable amino acids during this life stage. Funding Sources Canadian Institute of Health Research.

scholarly journals PSXI-34 Evaluating the lysine requirements of adult and senior Labrador Retrievers using low and high crude protein inclusion levels

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 322-322
Author(s):  
Jordan T Weil ◽  
Jessica L Varney ◽  
Jason W Fowler ◽  
Craig N Coon
Keyword(s):  
Amino Acid ◽  
Crude Protein ◽  
Control Diet ◽  
Isotope Ratio Mass Spectrometry ◽  
Acid Oxidation ◽  
Body Tissues ◽  
Labrador Retrievers ◽  
Best Fit ◽  
Atom Percent Excess

Abstract Despite consumer interest in senior pet care, little is known about the effect of changing crude protein (CP) levels on the lysine (Lys) requirements in young and senior dogs. Feeding crude protein in excess can lead to long-term health problems. Moreover, changing the CP content of the diet can lead differences in Lys requirements. Two experiments were conducted to determine the Lys requirements in adult and senior Labrador Retrievers through the indicator amino acid oxidation technique. Six young (< 1.5 yrs) and six old (>8 yrs) dogs were allocated to two trials (6 dogs/exp) to determine the effects of feeding 13 and 18% CP on the Lys requirement. All dogs were supplied with constant dietary Phe across diets. The control diet was fed for two days, followed by a day in which the test diet was fed, a tracer amino acid was supplied, and breath samples were collected. On test day, a priming dose of L-[1-13C]phenylalanine (Cambridge Isotope Laboratories, Inc.) based on the subject’s body weight was supplied, followed by [1-13C]Phe doses every 30 minutes, spanning a four hour period. A respiration mask was placed on each subject every 30 minutes (Oxymax, Columbus Instruments), 13CO2 was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a broken-line model of best fit (JMP® Pro 15). Oxidation results showed that for a 13% CP diet, the Lys mean and population safe requirements (mean±2SD) were 1.56±0.25 and 0.81±0.37 g/1000kcal for adult and senior dogs, respectively. For the 18% CP diet, adult and senior dog mean and population safe requirements were 1.36±0.18 and 0.86±0.07 g/1000kcal accordingly. The results suggest that as dogs age, the lowered lean mass requires less AA nitrogen and Lys to maintain body tissues.

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