Minimum methionine requirement in adult cats as determined by indicator amino acid oxidation.

There is a lack of empirical data on the dietary Met requirement, in the presence of Cys or cystine, in adult cats. Thus, the aim of this study was to determine the Met requirement, in the presence of excess Cys, in adult cats at maintenance using the indicator amino acid oxidation (IAAO) technique. Six adult neutered male cats were initially selected and started the study. Cats were adapted to the basal diet sufficient in Met (0.24% dry matter, DM) for 14 d prior to being randomly allocated to one of eight dietary levels of Met (0.10%, 0.13%, 0.17%, 0.22%, 0.27%, 0.33%, 0.38%, and 0.43% DM). Different dietary Met concentrations were achieved by supplementing the basal diet with Met solutions. Alanine was additionally included in the solutions to produce isonitrogenous and isoenergetic diets. Cats underwent a 2-d adaptation period to each experimental diet prior to each IAAO study day. On IAAO study days, 13 meals were offered corresponding to 75% of each cat's daily food allowance. The remaining 25% of their daily food intake was offered after each IAAO study. A bolus dose of NaH13CO3 (0.44 mg kg-1) and l-[1-13C]-phenylalanine (13C-Phe; 4.8 mg kg-1) were provided in fifth and sixth meals, respectively, followed by a constant dose of 13C-Phe (1.04 mg kg-1) in the next meals. Breath samples were collected and total production of 13CO2 was measured every 25 min through respiration calorimetry chambers. Steady state of 13CO2 achieved over at least three breath collections was used to calculate oxidation of 13C-Phe (F13CO2). Competing models were applied using the NLMIXED procedure in SAS to determine the effects of dietary Met on 13CO2. Two cats were removed from the study as they did not eat all meals, which is required to achieve isotopic steady. A breakpoint for the mean Met requirement, with excess of Cys, was identified at 0.24% DM (22.63 mg kg-1) with an upper 95% confidence limit of 0.40% DM (37.71 mg·kg-1), on an energy density of 4,164 kcal of metabolizable energy/kg DM calculated using the modified Atwater factors. The estimated Met requirement, in the presence of excess of Cys, is higher than the current recommendations proposed by the National Research Council's Nutrient Requirement of Dogs and Cats, the Association of American Feed Control Officials, and the European Pet Food Industry Federation.

The objective of this study was to determine the minimum Met requirement, when Cys was provided in excess, of adult cats using a highly sensitive and noninvasive technique, the indicator amino acid oxidation (IAAO). Six adult cats were fed experimental diets with varying levels of methionine (0.10%, 0.13%, 0.17%, 0.22%, 0.27%, 0.33%, 0.38%, and 0.43% on a dry matter [DM] basis) for 2 d prior to each IAAO study day. Although not all cats completed the study, a breakpoint was still defined in the statistical models applied, resulting in an estimated minimum Met requirement of 0.40% DM (37.71 mg kg−1), on an energy density of 4,164 kcal of metabolizable energy/kg DM calculated using the modified Atwater factors. The Met requirement, in the presence of excess of Cys, estimated in our study is higher than the current recommendations proposed by the National Research Council's Nutrient Requirement of Dogs and Cats, the Association of American Feed Control Officials, and the European Pet Food Industry Federation.

Determination of a steady-state isotope dilution protocol for carbon oxidation studies in the domestic cat.

The present study aimed to develop an isotope protocol to achieve equilibrium of 13CO2 in breath of cats during carbon oxidation studies using L-[1-13C]-Phenylalanine (L-[1-13C]-Phe), provided orally in repeated meals. One adult male cat was used in two experiments. In each experiment, three isotope protocols were tested in triplicate using the same cat. During carbon oxidation study days, the cat was offered thirteen small meals to achieve and maintain a physiological fed state. In experiment 1, the isotope protocols tested (A, B and C) had a similar priming dose of NaH13CO3 (0⋅176 mg/kg; offered in meal 6), but different priming [4⋅8 mg/kg (A) or 9⋅4 mg/kg (B and C); provided in meal 6] and constant [1⋅04 mg/kg (A and B) or 2⋅4 mg/kg (C); offered in meals 6-13] doses of L-[1-13C]-Phe. In experiment 2, the isotope protocols tested (D, E and F) had similar priming (4⋅8 mg/kg; provided in meal 5) and constant (1⋅04 mg/kg; provided in meals 5-13) doses of L-[1-13C]-Phe, but increasing priming doses of NaH13CO3 (D: 0⋅264, E: 0⋅352, F: 0⋅44 mg/kg; provided in meal 4). Breath samples were collected using respiration chambers (25-min intervals) and CO2 trapping to determine 13CO2:12CO2. Isotopic steady state was defined as the enrichment of 13CO2, above background samples, remaining constant in at least the last three samples. Treatment F resulted in the earliest achievement of 13CO2 steady state in the cat's breath. This feeding and isotope protocol can be used in future studies aiming to study amino acid metabolism in cats.

The development of a semisynthetic diet deficient in methionine for adult cats for controlled feline nutrition studies: effects on acceptability, preference, and behavior responses.

Chemically defined diets are commonly used in amino acid (AA) requirement studies to allow for tight control of AA delivery. However, those diets are not representative of commercial diets in the market and are unpalatable. Methionine (Met) is usually the first limiting AA in cat diets, but little is known about its requirement for adult cats. Thus, the objectives of this study were: 1) to develop a semisynthetic diet limiting in Met and evaluate its effect on acceptance and feeding behavior in cats; and 2) to evaluate the effect of different sources and inclusions of Met on preference in cats fed the semisynthetic diet. A semisynthetic diet deficient in Met and total sulfur AA (TSAA) was developed. Healthy adult male cats (n = 9) were fed (0800 and 1600 h) the semisynthetic diet top dressed with DL-Met solution (T-DLM), to meet 120% of the TSAA requirement, for 8 d. Feed intake was measured and a 30-min video recording was taken at the 0800 h feeding to evaluate feeding behavior of the cats. Following the acceptability trial, two bowl tests were performed where first choice was recorded and intake ratio was calculated as consumed food (A/A + B). Three combinations were tested: semisynthetic diet deficient in Met (T-BASAL) vs. T-DLM; T-BASAL vs. diet sufficient in Met provided 2-hydroxy-4-(methylthio)-butanoic acid (T-MHA); and T-DLM vs. T-MHA. Average feed intake remained high throughout the acceptability period (94.5% intake of total offered), but some cats decreased intake, resulting in a decrease in BW (≤2.5% of initial BW) over time (P < 0.05). Behaviors were similar among days (P > 0.05) with the exception of grooming the chest and body (P < 0.05). No preferences were observed towards a specific treatment (Met source and level) during the two-bowl tests (P > 0.05) and agreed with the cats expressing similar feeding behaviors during the preference tests (P > 0.05). In conclusion, a semisynthetic diet deficient in Met was successfully developed and can be used in studies to evaluate the effects of low protein and AA supplemented diets. Cats seem to show no preference for Met source and/or inclusion level in a semisynthetic diet application, which is of benefit for future studies aiming to determine the Met requirement in this species.

Previous studies that determined the requirement of amino acids (AA) in cats utilized experimental diets that do not represent commercial cat diets available in the market. Using this type of diets can present a challenge when applying AA requirements to commercial diet production. Thus, the goals of this study were to: 1) develop a semisynthetic diet deficient in methionine (Met) for adult cats with the inclusion of intact ingredients and to evaluate the effect of diet on behavior and acceptance; and 2) investigate the preference of a semisynthetic diet with different levels (deficient and sufficient) and sources [DL-Met and 2-hydroxy-4-(methylthio)-butanoic acid] of Met. The semisynthetic diet was well accepted by most cats. No major differences were observed in feeding behavior and preference towards Met source and level of inclusion. However, improvement in texture is recommended to increase acceptance and prevent removal of cats in feeding studies up to three weeks.

Applying the indicator amino acid oxidation technique in the domestic cat: results of a pilot study and development of a non-steady state prediction model.

The aim of this study was to evaluate whether the indicator amino acid oxidation (IAAO) method could be applied in the domestic cat. Six adult male cats were used in a replicated 3 × 3 Latin square design. Three semi-synthetic diets were developed: a methionine (Met) and total sulfur AA (TSAA) deficient diet (T-BASAL; 0.24% Met+Cys - DM basis) and two Met and TSAA-sufficient diets in which either dl-Met (T-DLM) or 2-hydroxy-4-(methylthio)-butanoic acid (T-MHA) were supplemented, respectively, on an equimolar basis to meet the TSAA requirement (0.34%). After a 2-d diet adaptation, IAAO studies were performed. Cats were offered 13 small meals. The sixth meal contained a priming dose (4.8 mg/kg-BW) of l-[1-13C]-Phe and the remaining meals a constant dose (1.04 mg/kg-BW). Breath samples were collected every 25 min to measure 13CO2 enrichment. The following morning, fasted blood samples were collected. Cats returned to the T-BASAL top dressed with a dl-Met solution for 4 d prior to being fed a new dietary treatment. Isotopic steady state was evaluated through visual inspection. Data were analyzed using PROC GLIMMIX procedure in SAS 9.4. While 13CO2 enrichment was successfully captured in breath samples, cats failed to reach 13CO2 steady state. Thus, a non-steady state isotope model was developed and coded in ACSLX (V3.1.4.2) individually for each cat on each study day to predict 13CO2 enrichment, and then, calculate oxidation of l-[1-13C]-Phe (F13CO2). A higher predicted F13CO2 was observed for cats fed T-BASAL compared to the others (P < 0.05), while no differences were observed between T-DLM and T-MHA (P > 0.05). Cats fed T-DLM tended to have higher plasma Met concentrations compared to those fed T-BASAL with cats fed T-MHA intermediate (P = 0.0867). Plasma homocysteine concentrations were higher in cats fed T-BASAL compared to the others (P < 0.05), while threonine concentrations tended to be higher in cats fed T-BASAL compared to those fed T-MHA (P = 0.0750). In conclusion, short-term provision of a semi-synthetic diet deficient in Met may elicit a metabolic response aiming to conserve Met. The successful quantification of 13CO2 enrichment in breath and the higher predicted F13CO2 in cats fed a Met deficient diet suggest that the IAAO technique may be used in cats. Adaptations in the isotope protocol should be made to achieve 13CO2 steady state in breath and avoid mathematical modeling to predict F13CO2.

It is necessary to apply more sensitive techniques to improve our limited understanding of amino acid (AA) requirements of adult cats. The non-invasive indicator amino acid oxidation (IAAO) technique is highly sensitive in mature animals. However, while it has been widely applied in different species, this technique has yet to be used in cats. We used six healthy adult cats to evaluate whether the IAAO method could be successfully applied in this species. A similar continuous small meals regimen as reported in IAAO studies in dogs was used. An oral primed-constant isotope infusion protocol was applied where l-13C-Phenylalanine (l-[1-13C]-Phe) was used as the tracer and the oxidation of l-[1-13C]-Phe as the response of interest. Breath samples were collected to determine enrichment of 13CO2 in breath and calculate oxidation of l-[1-13C]-Phe. While we were able to collect breath samples using calorimetry chambers and capture enrichment of 13CO2 in breath, cats did not achieve steady state, which is necessary to calculate oxidation of l-[1-13C]-Phe. Modifications in the isotope protocol should be made to achieve steady state of 13CO2 in breath, and thus, to successfully apply the IAAO technique to determine requirement of AA in adult cats.

Examining the Effects of Diet Composition, Soluble Fiber, and Species on Total Fecal Excretion of Bile Acids: A Meta-Analysis.

Bile acids (BA) are produced in the liver and conjugated with glycine or taurine before being released into the small intestine to aid with lipid digestion. However, excessive BA losses through feces can occur due to several dietary factors that in turn require greater production of BA by the liver due to a reduction in BA recycling. Consequently, net utilization of taurine and/or glycine is increased. To quantify this impact, we conducted a meta-analysis to investigate the effect of soluble fiber, diet composition, and species on fecal excretion of BA. After a systematic review of the literature, twelve studies met all inclusion criteria. Dietary carbohydrate, protein, fat, cellulose, cholesterol, soluble fiber and animal species were tested as independent variables. Mixed models were developed treating study as a random effect, and fixed effect variables were retained at P < 0.05 significance and where collinearity was absent between multiple X variables. A total of ten studies comprised of four species [(rat = 5), hamster (n = 1), guinea pig (n = 3) and dog (n = 1)], and 30 observations were evaluated in the final models after outlier removal. Model evaluation was based on the corrected Akaike Information Criteria, the concordance correlation coefficient and the root mean square prediction error. Three base models were developed, examining carbohydrate, protein and fat impacts separately. The best fitting models included the fixed effect of species and the interaction between soluble fiber (yes/no) and dietary carbohydrate, protein or fat (%, as-fed). Increased concentrations of dietary protein and fat resulted in greater fecal excretion of BA (P < 0.05). Conversely, increasing levels of dietary carbohydrate led to lower excretions of BA (P < 0.05). Increased dietary soluble fiber containing ingredients resulted in greater excretion of BA in all models (P < 0.05). Rats had greater excretion of BA compared to hamsters and guinea pigs (P < 0.05) in all models, and also compared to dogs (P < 0.05) in the carbohydrate model. The findings from this meta-analysis indicate that not only soluble fiber, but also increasing levels of dietary fat and protein may result in greater fecal excretion of BA, potentially altering taurine and/or glycine metabolism and affecting the need for diet delivery of these AA.

Short communication: the effects of a semi-synthetic diet with inclusion of black soldier fly larvae meal on health parameters of healthy adult cats.

In recent years, black soldier fly larvae meal (Hermetia illucens; BSFLM) has gained attention as a high value alternative protein source that is of great interest to the pet food industry. However, little is known regarding the effects of BSFLM on health parameters in adult cats. Thus, the objective of the current study was to determine the short-term effects of a semi-synthetic diet containing 4.6% inclusion of BSFLM on complete blood count (CBC) and serum biochemistry profile of healthy adult cats. Healthy adult male cats (n = 8; 1.4 yr) were fed the experimental diet for 21 d (experimental period) to maintain BW. Cats were washed in on a commercial diet and blood samples were collected before the start and at the end of the experimental period to measure gross health parameters. Results were analyzed as one-way ANOVA using the GLIMMIX procedure in SAS with cat as a random effect (SAS v. 9.4, The SAS Institute, Cary, NC). Cats lost an average of 5% of their BW (P = 0.0003) due to a concurrent decrease in food intake. A significant increase of alanine aminotransferase, chloride, potassium, sodium, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration was observed on day 21 vs. baseline (P < 0.05). In contrast, albumin, amylase, calcium, cholesterol, eosinophil, lymphocyte, monocyte, mean platelet volume, red blood cells, total protein, total solid proteins, and urea decreased over time (P < 0.05). However, all CBC and serum biochemistry parameters stayed within reference range for adult cats, with exception of glucose and mean corpuscular hemoglobin concentration that were above and below the reference range, respectively. Transient increases in glucose concentrations were likely due to sedation with dexmedetomidine prior to blood collection. The changes observed over time in the aforementioned parameters are likely due to changes in macronutrient composition of the diets offered prior to and during the experimental period (commercial diet vs. semi-synthetic diet, respectively) and cannot be attributed solely to a unique property of BSFLM. In conclusion, cats fed a semi-synthetic diet containing 4% BSFLM inclusion for 21 d remained healthy with no clinically relevant changes in CBC and serum biochemistry parameters. Further research should focus on longer term feeding studies and the ability of BSFLM to support the health and well-being of cats.

Characterization of white and red sorghum flour and their potential use for production of extrudate crisps.

In the human food industry, the wheat-free market sales have increased over the years due to awareness of wheat gluten allergy and celiac disease. Sorghum is a gluten-free grain with great potential to address shortcomings in this market. The aim of this study was to evaluate the milling process and flour quality of one white and one red sorghum varieties and evaluate extrusion as a potential process to produce sorghum crisps. The white and red sorghum grains were milled into flour in three production cycles. Flour quality was evaluated by determination of nutritional composition, pasting, and thermal profile. Extrusion processing of white and red sorghum flour was performed, and macrostructure of final product was evaluated. The white and red sorghum used in this study yielded similar flour content (P > 0.05). Chemical analyses revealed a higher protein and lower starch content for white sorghum than red sorghum flour (P < 0.05); however, their pasting properties did not differ. Initial and peak gelatinization temperatures were higher (P < 0.05) for red sorghum compared to white sorghum flour. Regarding particle size, white sorghum flour presented lower d10 and d50 compared to the red sorghum flour (P < 0.05). However, these differences did not impact the extrusion conditions, and white and red sorghum crisps had similar macrostructure characteristics. In conclusion, although differences in nutritional, thermal, and particle size properties were observed between the sorghum flours used in this study, changes in extrusion parameters were not needed in order to produce sorghum crisps with similar characteristics.

Effects of different carbohydrate sources on taurine status in healthy Beagle dogs.

This study evaluated the effects of a grain-based (GB) and grain-free (GF) diet on protein utilization and taurine status in healthy Beagle dogs. Two practical dog diets sufficient in crude protein, sulfur amino acids, and taurine content were formulated with the same ingredients with exception of the carbohydrate sources. The GB contained sorghum, millet, and spelt while potatoes, peas, and tapioca starch were used in the GF. A total of 12 Beagle dogs were used in a completely randomized design with six replicates per treatment. The study consisted of an adaptation period of 2 wk followed by an experimental period of 28 d in which GB and GF were fed to the dogs. At the end of the adaptation period and every 2 wk after it (day 0, day 14, day 28), markers of taurine metabolism were analyzed in whole blood (taurine), plasma (taurine, methionine, and cystine), urine (taurine:creatinine), and fresh fecal samples (primary and secondary bile acids). Fecal samples were collected during the last 6 d of experimental period for digestibly assessment using titanium dioxide as an external marker. Taurine markers and digestibility data were analyzed in a repeated measures model and one-way ANOVA, respectively, using PROC GLIMMIX in SAS (version 9.4). Apparent crude protein digestibility was not affected by treatment, but dogs fed GF diet had lower apparent organic matter digestibility compared with those fed GB (P < 0.05). Greater plasma taurine concentrations were observed at days 14 and 28 compared with day 0; wherein dogs fed GF exhibited greater increase compared to those fed GB (P < 0.05). Whole blood taurine concentrations, plasma methionine concentrations, and urinary taurine:creatinine were also greater at days 14 and 28 compared with day 0 (P < 0.05), but no effect of diet was observed. Total bile acid excretion was similar between GF and GB groups, but dogs fed GF excreted a higher proportion of primary bile acids compared with those fed GB (25.49% vs. 12.09% at day 28, respectively). In summary, overall taurine status was not affected by dietary treatments, however, our results suggest that the higher content of oligosaccharides and soluble fibers in the GF diet may alter the composition of the fecal bile acid pool.

Effect of ancient grains and grain-free carbohydrate sources on extrusion parameters and nutrient utilization by dogs.

The aim of this study was to evaluate the impact of ancient grain and grain-free carbohydrate sources on extrusion process, nutrient utilization, and palatability by dogs. Two maintenance dog diets were formulated with same proportions of carbohydrates: 1) ancient grain diet (AG) with spelt, millet, and sorghum; and 2) grain-free diet (GF) which had potato, peas, and tapioca starch. Experimental diets were extruded over 5 replicates in a completely randomized experimental design. Digestibility was carried out with 12 dogs in a switch-back experimental design. The GF diet required 22.6 and 25.9% more (P < 0.05) specific mechanical energy and in-barrel moisture input, respectively, than AG to produce kibbles out of the extruder with similar bulk density (P > 0.05). After drying, GF kibbles were less dense and more expanded, but harder than AG kibbles (P < 0.05). Dogs preferred GF over AG in the palatability assessment of uncoated kibbles. Apparent nutrient digestibility of dry matter, organic matter, gross energy, crude protein, and crude fat were not affected by treatment (P > 0.05). However, total dietary fiber (TDF) digestibility was 31.9% greater for dogs fed GF (P < 0.05). Moreover, wet fecal output was higher, and fecal dry matter was lower for dogs under GF (P < 0.05). The results demonstrated that GF and AG diets behaved differently during extrusion, but were similarly utilized by dogs, with exception of TDF. Thus, fiber content of grain-free diets should be monitored to maximize fecal quality.