• View in gallery

    Mean ± SEM values for 10 cats fed the LMCT diet (food consumption [black bars] and body weight [black triangles]) and 9 cats fed the HMCT diet (food consumption [white bars] and body weight [white circles]) during a 9-week feeding period. The initial week of dietary consumption was designated as week 0. Values did not differ significantly (P ≥ 0.05) between diets. Within a variable, values with different letters differ significantly (P < 0.05) among time points.

  • View in gallery

    Mean ± SEM body maintenance requirement (BMR) for 10 cats fed the LMCT diet (black bars) and 9 cats fed the HMCT diet (white bars) during a 9-week feeding period. Values did not differ significantly (P ≥ 0.05) between diets. See Figure 1 for remainder of key.

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Effects of dietary medium-chain triglycerides on plasma lipids and lipoprotein distribution and food aversion in cats

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  • 1 Department of Animal Science, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil; and Department of Small Animal Clinical Science, Comparative Nutrition Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.
  • | 2 Department of Animal Science, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil.
  • | 3 Department of Small Animal Clinical Science, Comparative Nutrition Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.
  • | 4 Nestlé Purina Pet Care Research, 3RN Checkerboard Sq, St Louis, MO 63164.
  • | 5 Nestlé Purina Pet Care Research, 3RN Checkerboard Sq, St Louis, MO 63164.
  • | 6 Department of Small Animal Clinical Science, Comparative Nutrition Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

Abstract

Objective—To determine possible diet aversion and lipid and lipoprotein alterations in cats fed diets containing medium-chain triglycerides (MCTs).

Animals—19 clinically normal adult female cats.

Procedures—Cats were assigned to 2 groups (low MCT diet [n = 10] and high MCT diet [9]) and fed the diets for 9 weeks according to metabolic body weight (100 kcal of metabolizable energy [ME] × kg−0.67/d). Daily consumption records and weekly body weight and body condition score (BCS) were used to adjust amounts fed and calculate daily ME factors for each cat to maintain ideal BCS. Blood samples were obtained after withholding food on days 0, 14, 28, and 56 for measurement of plasma triglyceride and total cholesterol concentrations and lipoprotein-cholesterol distributions. Repeated-measures ANOVA and Tukey multiple comparison tests were performed.

Results—No diet differences were found for food consumption, body weight, BCS, and ME factors. A significant increase in plasma triglyceride concentration was detected for the high MCT diet; however, values were within the reference ranges. No diet effects were observed for total cholesterol concentrations or lipoprotein-cholesterol distributions, although increases over time were observed.

Conclusions and Clinical Relevance—Inclusion of MCT in diets of cats did not result in feed refusal and had minimal effects on lipid metabolism. Such diets may be useful for both clinically normal cats and cats with metabolic disorders. The MCT oils are an example of a bioactive dietary lipid that may benefit feline metabolism and can serve as a useful functional food ingredient for cats.

Abstract

Objective—To determine possible diet aversion and lipid and lipoprotein alterations in cats fed diets containing medium-chain triglycerides (MCTs).

Animals—19 clinically normal adult female cats.

Procedures—Cats were assigned to 2 groups (low MCT diet [n = 10] and high MCT diet [9]) and fed the diets for 9 weeks according to metabolic body weight (100 kcal of metabolizable energy [ME] × kg−0.67/d). Daily consumption records and weekly body weight and body condition score (BCS) were used to adjust amounts fed and calculate daily ME factors for each cat to maintain ideal BCS. Blood samples were obtained after withholding food on days 0, 14, 28, and 56 for measurement of plasma triglyceride and total cholesterol concentrations and lipoprotein-cholesterol distributions. Repeated-measures ANOVA and Tukey multiple comparison tests were performed.

Results—No diet differences were found for food consumption, body weight, BCS, and ME factors. A significant increase in plasma triglyceride concentration was detected for the high MCT diet; however, values were within the reference ranges. No diet effects were observed for total cholesterol concentrations or lipoprotein-cholesterol distributions, although increases over time were observed.

Conclusions and Clinical Relevance—Inclusion of MCT in diets of cats did not result in feed refusal and had minimal effects on lipid metabolism. Such diets may be useful for both clinically normal cats and cats with metabolic disorders. The MCT oils are an example of a bioactive dietary lipid that may benefit feline metabolism and can serve as a useful functional food ingredient for cats.

Medium-chain triglycerides are readily found in products such as coconut oil and milk by-products. They contain 8 to 12 carbon atoms with no double bonds. By contrast, LCTs typically contain ≥ 14 carbon atoms and may be saturated or unsaturated. Because of their low molecular weight and higher water solubility, compared with those of LCTs, MCTs are more readily digested and absorbed, which results in a more rapid transport to the liver via the portal circulation.1 During digestion, the low molecular weight of MCTs facilitates the action of pancreatic lipase, which enables the ready release and absorption of free fatty acids and monoacylglycerol.2 After absorption, triacylglycerol is reesterified by acyl-CoA synthetase, but this enzyme has greater affinity for LCTs than for MCTs. Consequently, a major portion of absorbed MCTs directly enter the portal venous circulation, are bound to albumin, and are transported directly to the liver.1–3 By comparison, LCT fatty acids typically are resynthesized into triacylglycerols, incorporated into chylomicrons, and transported via the lymphatic system to the thoracic duct, thus initially bypassing the liver.3 Once in the liver, MCFAs may follow various catabolic pathways, including β-oxidation, Ω-oxidation, and peroxisomal oxidation or elongation to other fatty acids.4 In tissues, transfer of MCFAs into mitochondria for β-oxidation is typically a carnitine-independent event.5 However, some studies6,7 in which investigators used 12-carbon fatty acids (ie, C12:0) revealed that carnitine transport may provide at least a minor pathway for C12:0 metabolism. Although the bulk of fatty acid catabolism is via mitochondrial β-oxidation, there also may be triacylglycerol reesterification via fatty acid synthetase. However, this latter pathway is more effective with fatty acids of ≥ 14 carbons than with MCFAs. Consequently, few dietary MCFAs are recovered per se in triacylglycerol, phospholipid, or cholesterol ester fractions of plasma or tissues.3

Because of the unique metabolism of MCTs, dietary MCT supplementation may be beneficial in several respects. For example, MCTs may be used for animals with malabsorptive and maldigestion disorders as well as exocrine pancreatic insufficiency, lymphangiectasia, or chylothorax.8 Some effects of MCTs have also been evaluated in obesity management because the energy content of MCTs is less than that of LCTs and postprandial energy expenditure increases when MCTs are used.3 Thus, diets containing MCTs may help during weight reduction and for health maintenance after weight loss. Other possible benefits of MCT oils include effects of parenteral infusion of MCTs on the immune system and improvement of cardiac energetics and contractile function in certain cardiac disorders.9,10 In addition, no toxicologic effects of MCT oils have been reported in humans or other animals when administered orally or parenterally or when consumed as a dietary supplement in a balanced diet at amounts of up to 15% of energy.11

Despite these potential benefits, food aversion in dogs and cats has been detected when MCTs are included in diets. This effect was especially pronounced when caprylic acid (ie, C8:0) was fed.12 Poor palatability of various MCT oils has been reported by several authors.13–15 In cats, food aversion was detected for diets with 0.1% caprylic acid and 5.0% MCT containing purified caprylic acid.12 In dogs, purified diets containing 22% of ME as MCTs caused a reduction in consumption and an increase in plasma lipid concentrations.16 However, when dogs were fed a diet containing 11% of ME as MCTs, no refusals were detected and a slight increase in crude fat digestibility was observed. Also, plasma triacylglycerol concentrations increased by 23% in the groups that received MCTs, compared with results for the control group.17 However, it is important to mention that purified or semipurified diets were used in all of these aforementioned studies.

The study reported here was conducted with natural-source ingredients by replacing safflower oil with coconut oil to achieve a diet with 11% of ME as MCTs in a complete and balanced diet. Acceptance of this diet as well as its possible effects on lipid metabolism in cats was investigated. The objective was to feed the diets to achieve and maintain body weights of cats and equalize their metabolism at steady state while achieving a BCS of 5 of 9.

Materials and Methods

Animals—Nineteen adult sexually intact female cats ranging between 1.5 and 2 years of age with a body weight between 2.4 and 6.0 kg were used in the study. The cats were assessed and considered to be clinically normal prior to entering the study as determined on the basis of results of physical examination (performed by one of the authors [LT]), a CBC, serum biochemical analysis, and a thyroxine stimulation test and measurement of triiodothyronine concentrations. An initial BCS (scale of 1 to 9, with 5 considered ideal) was determined for each cat during a 4-week preexperimental diet period and prior to onset of the feeding study. Sixteen cats had a BCS of 5 or 6. Of the 3 remaining cats, 1 had a BCS of 8 and the other 2 each had a BCS of 7. The BCS of each cat was assigned by the same investigator (LT) to minimize variation and observer bias during the course of the study. Cats were housed individually in kennels in accordance with established guidelines.18 Study protocols were approved by the Texas A&M University Animal Care and Use Committee.

Diets and feeding procedures—Cats consumed a preexperimental diet for 4 weeks prior to the onset of the feeding trial and then were fed the experimental diets for 9 weeks (Appendix 1). The preexperimental diet was a commercially available extruded dry cat fooda that was complete and balanced. It was purchased locally and contained a minimum of 30% crude protein, minimum of 8% crude fat, maximum of 4.5% crude fiber, and minimum of 12% moisture. During the preexperimental diet period, body weight and BCS of each cat were determined weekly and food consumption was determined daily. Cats were fed in the morning, and all cats consumed their ration quickly (usually within the first few hours after feeding). All cats were fed on the basis of their individual metabolic weights (100 kcal of ME × kg−0.67/d).19 Modifications of the amount fed were made, when necessary, to maintain each cat's BCS at 5. Cats were stimulated every week (playing with paper bags) to provide physical activity. Feeding the measured amounts of the diet and providing physical activity helped control the body weight of each cat for the most part. As mentioned previously, 3 of the cats had initial higher BCS scores and appeared resistant to changes (decreases) in BCS.

All cats were assigned by use of a randomization procedure into 2 groups. Cats in each group received a specific diet (HMCT [n = 9] or LMCT [10]). The experimental diets were formulated to be complete and balanced to meet or exceed minimal nutrient requirements for adult cats (Appendix 2).20,21 They were manufacturedb as dry, extruded products. The 2 experimental diets were similar in all aspects, except for fatty acid type, and varied only in the relative amounts of coconut oil (which is rich in MCTs) and safflower oil (which is rich in linoleic acid). The expected nutrient compositions of the experimental diets were 35% protein, 18% fat (acid hydrolyzed), 7.5% ash, 8% moisture, and 2% crude fiber. After manufacture, the diets were analyzed by the analytic laboratory of the manufacturerc and found to be within expected analytic variance of these target values.

During the experimental period, the cats were fed their respective diet once daily for 9 weeks (the first week of feeding the HMCT or LMCT diets was designated as week 0). The cats were fed the HMCT and LMCT diets in accordance with their individual weekly metabolic weight (100 kcal of ME × kg−0.67/d) to maintain a BCS of 5.19 Food consumption and body maintenance energy requirement were recorded after 24 hours, and a mean value was calculated for each week and used for statistical analysis. On the basis of weekly weight evaluations, it was necessary to reduce caloric intake to 80 kcal of ME × kg−0.67 in the 3 cats that had a BCS of 7 or 8 at the beginning of the study because they appeared resistant to decreases in the BCS when fed at the recommended amounts for the other cats.

Collection and analysis of samples—Blood samples were obtained via venipuncture from each cat at weeks 0, 2, 4, and 8 during the experimental period. Food was withheld for 12 hours before blood collection, and 7 mL of blood was collected from a saphenous vein into EDTA-containing tubes. At week 0, a CBC and plasma biochemical analysis were performed. Blood samples were centrifuged at 1,825 × g for 15 minutes, and plasma was separated in small aliquots and frozen at −80°C. Triglyceride and TC concentrations were determined by use of enzymatic methods.22 The LP-C distributions in fresh plasma were determined by use of electrophoresis on 1% agarose gels. Gels were stained and LP-C distributions quantified by use of scanning densitometry; results were reported as β–, pre-β–, and α–LP-C fractions.22 At the conclusion of the study, all cats were assessed via a physical examination and laboratory hematologic analyses.

Digestibility assay—A digestibility evaluation was conducted during week 6. All the feces from each cat were collected twice a day for 5 consecutive days and frozen at −20°C. All samples, including feces and diets, were sent to the analytic laboratory of the diet manufacturerc for analysis. Criteria evaluated were coefficients of digestibility from crude protein, total fat, crude fiber, and ash and gross energy measurements. The coefficient for digestible energy was calculated, and ME was calculated on the basis of digestible energy and urinary loss.21

Statistical analysis—Values were reported as mean ± SEM. All data, except for the BCS data, were normally distributed as determined by use of the Shapiro-Wilk test. The BCS values were analyzed by use of a nonparametric test (Kruskal-Wallis 1-way ANOVA).d Digestibility coefficients were compared between diet, time, and the diet × time interaction and tested by use of a general linear model.e For all other data, significant differences were evaluated by use of a repeated-measures ANOVAf with diet, time, and the diet × time interaction for plasma variables (triglyceride and TC concentrations and the LP-C fractions), food consumption, body weight, and metabolic factor. For all variables, the Tukey multiple comparison of means was performed when appropriate. For all analyses, values of P < 0.05 were considered significant.

Results

Dietary and energy consumption—For the most part, all cats readily consumed the diets at the time the diets were offered; all diets were consumed within 4 hours after feeding. No diet refusals were observed for the HMCT or LMCT diets. Two cats consumed a smaller number of calories than was fed to the other cats, but they were not in the same diet group. No diet effects were observed during the study, and total energy consumption or amounts of food consumed per week also did not differ significantly (P = 0.944). However, a significant time effect on weekly energy consumption was detected between week 0 and weeks 5 and 7 (Figure 1). Although the energy densities of the experimental diets were approximately equal, the preexperimental diet had less energy per kilogram of dry matter, more nitrogen-free extract, and less fat than did the experimental diets (Appendix 2).

Figure 1—
Figure 1—

Mean ± SEM values for 10 cats fed the LMCT diet (food consumption [black bars] and body weight [black triangles]) and 9 cats fed the HMCT diet (food consumption [white bars] and body weight [white circles]) during a 9-week feeding period. The initial week of dietary consumption was designated as week 0. Values did not differ significantly (P ≥ 0.05) between diets. Within a variable, values with different letters differ significantly (P < 0.05) among time points.

Citation: American Journal of Veterinary Research 71, 4; 10.2460/ajvr.71.4.435

Body weight and BCS—The cats had a modest but significant (P = 0.026) weight loss between weeks 0 and 8, but body weights did not differ significantly (P = 0.595) between the diets (Figure 1). Although 3 cats began the study at a BCS of 7 or 8, 2 reached the desired BCS (5 or 6) by the end of the experimental period, whereas the remaining cat had a BCS of 7. No significant differences for BCS were detected between diets (P = 0.270) and over time (P = 0.057) during the study. All cats were clinically normal at the end of the study (data not shown).

Maintenance energy requirement—No significant (P = 0.575) difference was detected between the HMCT and LMCT diets with regard to energy needed to meet maintenance energy requirements of the cats. Furthermore, energy requirements were stable throughout the study, even though a significant (P < 0.001) difference was detected when values for week 0 were compared with values for the subsequent weeks (Figure 2).

Figure 2—
Figure 2—

Mean ± SEM body maintenance requirement (BMR) for 10 cats fed the LMCT diet (black bars) and 9 cats fed the HMCT diet (white bars) during a 9-week feeding period. Values did not differ significantly (P ≥ 0.05) between diets. See Figure 1 for remainder of key.

Citation: American Journal of Veterinary Research 71, 4; 10.2460/ajvr.71.4.435

Plasma lipid variables—A significant (P < 0.001) time effect was detected for plasma cholesterol concentrations for all cats beginning at week 2, with a maximal increase detected at week 4. However, no differences between diets were detected. The α–LP-C fraction was similarly increased over time and was increased by 67% at week 4, compared with the value for week 0. This fraction was responsible for most of the increase in TC concentration, although the other LP-C fractions also contributed (but to a lesser extent) to this increase over time (Table 1). The pre-β–LP-C fraction had a similar pattern, with a significant (P < 0.001) effect of time and a maximal value at week 2 but decreases until week 8, at which time it had similar values to those found at week 0. However, a significant (P = 0.035) diet × time interaction was evident for this fraction (Table 2). Thus, cats fed the HMCT diet had an increase in the pre-β–LP-C fraction at week 4, compared with results for cats fed the LMCT diet, which returned to basal (week 0) values at week 8. The β–LP-C fraction also increased but remained increased at week 8, which was in contrast to results for the other LP-C fractions.

Table 1—

Mean ± SEM plasma lipid and LP-C concentrations in 9 adult cats fed the HMCT diet and 10 cats fed the LMCT diet for 9 weeks.

VariableDietP valueTime of study (wk)*P valueDiet × time interaction P value
HMCTLMCT0248
β–LP-C0.57 ± 0.040.62 ± 0.040.6780.36 ± 0.06a0.65 ± 0.04b0.72 ± 0.06b0.65 ± 0.04b< 0.0010.960
Pre-β–LP-C0.80 ± 0.050.70 ± 0.050.1140.67 ± 0.08a,b0.93 ± 0.05c0.83 ± 0.06a,c0.59 ± 0.07b< 0.0010.035
α–LP-C2.80 ± 0.182.71 ± 0.130.8172.09 ± 0.14a2.38 ± 0.13b3.49 ± 0.21c3.13 ± 0.22c< 0.0010.233
TC4.19 ± 0.224.06 ± 0.170.7813.10 ± 0.22a3.93 ± 0.20b5.07 ± 0.25c4.37 ± 0.25b< 0.0010.184
Triglycerides0.29 ± 0.02a0.24 ± 0.01b0.0230.27 ± 0.02a,b0.28 ± 0.02a,b0.29 ± 0.02a0.24 ± 0.01b0.0160.112

Values are reported as μmol/L.

Initial week of feeding the HMCT or LMCT diet was designated as week 0.

Values were considered to differ significantly at P < 0.05.

Within a row, means with different superscript letters differ significantly (P < 0.05).

Table 2—

Mean ± SEM values for pre-β–LP-C concentrations in 9 adult cats fed the HMCT diet and 10 cats fed the LMCT diet for 9 weeks.

DietTime of study (wk)*
0248
HMCT0.68 ± 0.13a,b0.96 ± 0.04a,b0.97 ± 0.09a0.61 ± 0.10b
LMCT0.66 ± 0.090.88 ± 0.100.66 ± 0.060.59 ± 0.11

Values are reported as μmol/L.

See Table 1 for remainder of key.

Both time (P = 0.016) and diet (P = 0.023) significantly affected plasma triglyceride concentrations (Table 1). Feeding the HMCT diet resulted in significantly (P = 0.040) higher triglyceride concentrations, compared with results for cats fed the LMCT diet. Time effects included a maximal increase of mean plasma triglyceride concentrations at week 4 that decreased to the basal (week 0) concentration at week 8.

Digestibility assay—No significant effects were found for any variables tested (data not shown). Apparent total fat digestibility was 93.22% for the HMCT diet and 92.12% for the LMCT diet.

Discussion

To our knowledge, the study reported here is the first in which it is described that cats will readily consume MCT-containing natural-ingredient diets without refusal. This finding is in contrast to results of several earlier studies13–15 in cats and other species in which investigators observed feed refusal when MCTs were included in the diets, all of which were semipurified-type diets. It should be mentioned that dietary oils containing MCTs do not have unpleasant odors or taste, at least as judged by human subjects. By contrast, MCFAs in their nonesterified form may have an objectionable flavor or odor often associated with goats.23 It should also be mentioned that most of the earlier studies involved the use of higher amounts of MCTs or nonesterified MCFAs, typically ≥ 22% of ME. Another important factor for consideration is the type of MCTs fed. Purified triglycerides, such as tricaproin (C6:0), tricaprylin (C8:0), tricaprin (C10:0), and trilaurin (C12:0), have been investigated,9 whereas mixed MCTs from coconut oil were used in the study reported here.

One important objective of our study was to verify acceptance of practical diets containing MCT oils by cats. For this reason, coconut oil was used as a source of MCTs. Coconut oil contains approximately 50% of total fat as MCTs, whereas LCTs constitute the other fatty acid portion. This blend of fatty acids is most likely the reason for acceptance by cats in this study, compared with acceptance of purified MCT oils fed exclusively. In dogs, diets containing 11% MCTs with increased crude fat digestibility were also readily consumed.17

The reason for feed refusal in cats fed purified MCTs is unknown. However, some properties of these dietary triglycerides may affect palatability. Diets containing free MCFAs (0.1% caprylic acid) were refused by cats, presumably because of an objectionable taste.12 Because MCTs are more water soluble than are LCTs, they may be more readily released from the triglyceride molecule in aqueous solution despite the lack of lingual lipase in feline species.1,3 Thus, the possibility exists that there may have been some partial hydrolysis in the mouths of cats fed purified MCTs, which led to MCFA release and thereby affected taste. By contrast, food intake was not affected after intragastric administration of LCTs, compared with after administration of MCTs,24 which eliminated a systemic effect on satiety and food intake. Consequently, feed refusal in earlier studies23 in which purified MCTs were used may have been related to physical events in the mouth or oral cavity or at the taste receptors. Additionally, triglycerides containing both MCFAs and long-chain fatty acids may have different olfactory properties or hydrolysis patterns, which in turn, may also impact palatability.

As indicated, 3 cats had a BCS score > 5 (ie, greater than ideal BCS) at the time they entered the study. In these cats, the amount of energy fed was reduced so that they would achieve the desired BCS. Because energy requirements are inversely proportional to fat mass, the number of calories needed to maintain fat tissue is much lower than that needed to maintain lean tissues.21 The small loss of body weight during the initial week of the study was only during adaptation to the experimental diets because the cats received fewer total calories than in subsequent weeks.

The metabolic factor recommended in the NRC report21 on nutrient requirements for adult cats was used as a starting point to determine the amount of diet that should be fed to sexually intact cats in the study (ie, 100 kcal of ME × kg−0.67/d). However, because the actual amount of diet consumed that was needed to maintain ideal BCS was recorded each day, the actual mean metabolic constant could be calculated and compared with the value in the NRC report. As a result, this calculated constant was similar to that found in the NRC report21 and helps substantiate current energy recommendations for the feline species. This factor is calculated as the ratio between food consumption and metabolic body weight and can be used to compare energy metabolism between diets. It was helpful in this study because it was used to estimate the amount of daily energy necessary to maintain a BCS of 5 of 9 and is most useful when applied to animals with the same BCS. When animals do not have the same BCS, it is difficult to make comparisons because maintenance energy varies according to the relative amounts of lean and fat mass in each animal.g

Regarding alterations in lipid metabolism, studies25–27 in humans have revealed hypercholesterolemia associated with low-density lipoprotein fractions when MCTs are fed, compared with results when LCTs are fed. In dogs, both plasma TC and triglyceride concentrations were increased by 70% and 80%, respectively, when 22% of ME as MCTs was included in the diet.16 Dogs fed diets containing 11% of ME as MCTs also typically had increases in triglyceride concentration of 23% but with no effect on low-density lipoprotein fractions.17 Thus, our study in cats found similar effects on lipid metabolism as was observed in dogs fed the same amount of MCT (ie, 11% of ME as MCTs).

Time effects that resulted in increases in plasma triglyceride and TC concentrations in the present study were likely related to increased fat content of the experimental diets, compared with the fat content of the preexperimental diet. Increased amounts of dietary MCTs did not appear to modify this effect. Although the preexperimental diet contained 12% crude fat on a dry-matter basis, the LMCT and HMCT diets contained 19.9% and 18.2% crude fat on a dry-matter basis, respectively. However, the triglyceride and TC concentrations never exceeded the upper limit of the reference range for cats at any time point. Furthermore, the increase in triglyceride concentrations observed with the HMCT diet coincided with an increase in the pre-β–LP-C fraction (ie, the very–low-density lipoprotein fraction). Diets high in MCTs may promote an increase in β-oxidation, which generates more acetyl-CoA1 and, during positive energy balance, subsequently stimulates triacylglycerol synthesis and an increase in production of very–low-density lipoproteins.27,28 There was a slightly higher total fat content in the LMCT diet, compared with that of the HMCT diet; however, had both diets been precisely equivalent in total fat content, it is possible that the increase in triglyceride concentration detected with the HMCT diet may have been even slightly higher. However, this remains to be determined.

Increases in plasma TC concentrations were specifically associated with the α–LP-C fraction that corresponds to a high-density lipoprotein fraction. Lipoprotein metabolism is unique in dogs and cats, compared with that in humans. In humans, the fraction often associated with hypercholesterolemia is β–LP-C, which corresponds to the low-density lipoprotein fraction. However, in dogs and cats, it is the α–LP-C fraction (ie, high-density lipoprotein fraction) that is most frequently increased with hypercholesterolemia, and it is this phenomenon that helps protect these species against atherogenesis and coronary artery diseases and their complications.28,29

In the study reported here, cats readily consumed an MCT-containing diet with no refusal when fed in amounts needed to maintain ideal body condition. The lower amount of energy provided by MCTs (11% of ME as MCTs) and a natural source of fat (ie, coconut oil) may explain consumption of the HMCT diet, compared with aversion to consumption of diets with purified oils. Thus, coconut oil may be considered as an ingredient for inclusion in diets formulated for cats. Because of results of studies in other species, including humans, diets that incorporate MCTs may also have the potential to help manage cats with metabolic disorders such as malabsorption syndromes because of the unique digestion and metabolism in felids. Although modest increases in plasma triglyceride and TC concentrations were observed in this study, none of these changes were found to be in excess of reference limits. Thus, MCT oils are an example of a bioactive lipid that may benefit metabolism of cats29,30 and can serve as a useful functional food ingredient30 for domestic cats.

ABBREVIATIONS

BCS

Body condition score

HMCT

High medium-chain triglyceride

LCT

Long-chain triglyceride

LMCT

Low medium-chain triglyceride

LP-C

Lipoprotein-cholesterol

MCFA

Medium-chain fatty acid

MCT

Medium-chain triglyceride

ME

Metabolizable energy

NRC

National Research Council

TC

Total cholesterol

a.

Kit N Kaboodle cat food, Nestlé-Purina Pet Care, St Louis, Mo.

b.

Nestlé-Purina Product Technology Center, St Louis, Mo.

c.

Nestlé-Purina Analytical Laboratories, Nestle Purina Pet Care Co, St Louis, Mo.

d.

SAS, version 9.0, SAS Institute Inc, Cary, NC.

e.

PROC GLM ANOVA, SAS, version 9.0, SAS Institute Inc, Cary, NC.

f.

PROC Mixed, SAS, version 9.0, SAS Institute Inc, Cary, NC.

g.

Pouteau E, Mariot S, Martin L, et al. Effects of weight variations (fattening and slimming) on energy expenditure in dogs (abstr). J Vet Intern Med 2000;390.

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Appendix 1

Fatty acid concentration in the preexperimental,* LMCT, and HMCT diets fed to cats.

Fatty acidDiet
PreexperimentalLMCTHMCT
C6:0ND< 0.100.40
C8:0ND2.296.00
C10:0ND2.275.01
C12:0ND16.5143.40
C18:2(n-6)15.0471.0020.80
C20:4(n-6)0.260.340.35
Total saturated3168113
Total monounsaturated325545
Total polyunsaturated167423

Values are reported as g/kg of dry matter and represent the mean of 2 determinations performed in duplicate. Values were deemed acceptable when 95% of the absolute differences between duplicates were < 2 SDs of the difference.

The preexperimental diet was a commercially available dry extruded cat food.a

ND = Not detected.

Appendix 2

Nutrient profile of the preexperimental,* LMCT, and HMCT diets fed to cats.

NutrientDiet
PreexperimentalLMCTHMCT
Crude protein (g/kg of dry matter)341355349
Nitrogen-free extract (g/kg of dry matter)483351378
Fiber (g/kg of dry matter)451820
Ash (g/kg of dry matter)757770
Total fat (g/kg of dry matter)132199182
Energy (ME kcal/kg of diet on an as-fed basis)3.5254.3204.330

Amount of total fat was determined by extraction and gravimetric analysis with ash content estimated at 7.5%.

Values for the LMCT and HMCT diets were obtained by use of digestibility analysis; value for the preexperimental diet was calculated.

Ingredients (on a wt/wt basis) for the LMCT and HMCT diets were as follows: brewers milled rice, 35.9%; soybean protein isolated, 23.3%; chicken whole carcass and parts, 21.6%; soybean hulls, 3.67%; dicalcium phosphate, 2.93%; coconut oil, 2.80%; flavor coating, 1.5%; beef tallow, 0.7%; potassium chloride, 0.65%; mineral premix, 0.34%; choline chloride, 0.32%; calcium carbonate, 0.29%; sodium chloride, 0.22%; DL-methionine, 0.18%; taurine, 0.1%; vitamin premix, 0.07%; and vitamin E (50%), 0.03%.

Contents of the mineral mix (g/kg of dry matter) were as follows: zinc (as zinc sulfate), 65; iron (as ferrous sulfate), 39; manganese (as manganese sulfate), 18.25; copper (as copper sulfate), 3.2; iodine (as calcium iodate), 651; and selenium (as selenium selenite), 50. Contents of the vitamin premix (g/kg of dry matter) were as follows: nicotinic acid, 146.32; vitamin A acetate, 10.35; DL-α-tocopherol acetate, 90; cholecalciferol, 84; thiamine mononitrate, 52; calcium D-pantothenate, 51.06; riboflavin, 24.4; pyridoxine hydrochloride, 14.52; folic acid, 6; menadione sodium bisulfite, 508; vitamin B-12, 93; and biotin, 36.8. The remainder of each diet consisted of 2 dietary oils (coconut oil, 5.24% in the HMCT diet; safflower oil, 5.58% in the LMCT diet).

See Appendix 1 for remainder of key.

Contributor Notes

Supported by Nestlé-Purina Pet Care and the Mark L. Morris Professorship in Clinical Nutrition, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Tex.

Dr. Trevizan was supported by a student sponsorship from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of the Government of Brazil.

Address correspondence to Dr. Bauer (jbauer@cvm.tamu.edu).