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Nutrient Requirements and Optimal Nutrition

The (n-3) Fatty Acid Dose, Independent of the (n-6) to (n-3) Fatty Acid Ratio, Affects the Plasma Fatty Acid Profile of Normal Dogs¹

² Department of Biomedical Sciences, College of Veterinary Medicine; Oregon State University, Corvallis, OR 97331-4802; ³ Science and Technology Center, Hill's Pet Nutrition, Topeka, KS 66617-1587; and ⁴ Human Nutrition Research Laboratory, Department of Nutrition, School of Human Environmental Sciences, University of North Carolina, Greensboro, NC 27402-6170

^*To whom correspondence should be addressed. E-mail: jean.hall{at}oregonstate.edu.

	ABSTRACT

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
The purpose of this study was to determine whether the dose of (n-3) fatty acids (FA) administered, independent of the relative ratio of (n-6) to (n-3) FA in the food, influences plasma FA composition in dogs. Healthy female, geriatric beagles (7–10 y old) were fed foods containing (n-6) to (n-3) FA ratios of either 40.0:1 or 1.4:1 for 12 wk (study 1) or 36 wk (study 2). In study 3, beagles were fed food with the same 1:1 ratio of (n-6) to (n-3) FA, but with increasing concentrations of (n-6) and (n-3) FA. Plasma FA concentrations were measured after completing the feeding studies. In studies 1 and 2, dogs fed fish oil–enriched food with a high (n-3) FA concentration had higher plasma total (n-3) FA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) concentrations and lower plasma total (n-6) FA, linoleic acid, and arachidonic acid concentrations than dogs fed corn oil–enriched food with a low (n-3) FA concentration (P < 0.001). Both inclusion of fish oil (P < 0.001) and increased food intake independent of treatment effects increased the plasma DHA (P = 0.05) concentration. Furthermore, constancy of the dose of (n-3) FA administered over long periods of time was necessary to maintain plasma levels of total (n-3) FA, EPA, and DHA. In study 3, up to certain dietary concentrations (6.3 g total (n-3) FA/kg food for DHA and 9.8 g total (n-3) FA/kg food for EPA), the dose of (n-3) FA administered, independent of the (n-6) to (n-3) FA ratio, determined the plasma (n-3) FA composition. Results from our studies indicate that 175 mg DHA/(kg body weight · d) is required to attain maximum plasma levels of DHA.

	Introduction

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

Consuming fish oil, which contains large amounts of (n-3) PUFA, results in partial replacement of arachidonic acid (AA) in cell membranes by eicosapentaenoic (EPA) and DHA. This leads to decreased production of AA-derived mediators of inflammation, e.g., leukotriene (LT) B₄ and PGE₂ (1,9). In addition, (n-3) FA have a number of other effects that occur downstream of altered eicosanoid production or are independent of this. For example, they result in suppressed production of proinflammatory cytokines and can modulate adhesion molecule expression (10). These effects occur at the level of altered gene expression (10).

However, evidence as to whether these beneficial effects in dogs are the result of the absolute dose of (n-3) FA administered or whether the ratio of (n-6) to (n-3) FA in the food plays a critical role is not readily available. Studies with rat tissue (11) and human plasma (12) show that the mixture of 20- and 22-carbon PUFA maintained in plasma and tissue phospholipids is hyperbolically related to the dietary intake of linoleic acid [LA, 18:2 (n-6)] and -linolenic acid [ALA, 18:3 (n-3)]. On the other hand, LA and ALA are maintained in tissue triacylglycerols in linear proportion to their dietary abundance, expressed as percentage of daily energy. Bauer et al. (13) described second-order curvilinear equations for dogs that predict the relation between dietary LA and ALA concentration, and resultant plasma FA concentration of triglycerides, and found them valid up to 28 energy % LA and 20 energy % ALA. In addition, analysis of phospholipid FA in dogs supports the concept of a competitive and saturable hyperbolic relation between dietary PUFA and plasma and tissue long chain PUFA accumulation in dogs. Using complex equations, Bauer et al. (13) suggested that plasma concentrations of triglyceride LA or ALA, and possibly tissue enrichments, could be predicted prior to the actual feeding of foods containing varying (n-6) and (n-3) PUFA concentrations. However, it is unclear from their study if the dose of (n-6) or (n-3) FA consumed by dogs per kg body weight was assessed. Also, it is not clear whether maintaining the dietary ratio of (n-6) to (n-3) FA while increasing the total intake of (n-6) and (n-3) FA affects the predictive value of these equations.

The purpose of our study was 3-fold. First, we sought to compare changes in plasma FA profiles of dogs given food that contained high levels of (n-3) FA versus food that contained high levels of (n-6) FA to determine whether individual differences in food intake significantly affected plasma FA profiles (study 1). Second, we wanted to determine whether dogs fed the same food over a 36-wk period maintain stable plasma FA profiles (study 2). Third, we wanted to determine the effect of foods with the same ratio, but increasing concentrations of (n-6) and (n-3) FA, on plasma concentrations of these FA (study 3).

	Materials and Methods

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
    Dogs. Thirty-two healthy, female, geriatric (7–10 y old) beagles that weighed between 7.6 and 15.3 kg were maintained according to currently accepted practices of good animal husbandry (14). All dogs had been immunized against canine distemper, parvovirus, and rabies, and none had chronic systemic disease on the basis of results of physical examination, complete blood count determination, serum biochemical analyses, urinalysis, and fecal examination for parasites. Dogs were housed in pairs in indoor runs and fed once daily in the morning. Dogs experienced enrichment through interactions with each other and with the caretakers. The experimental protocol was reviewed and approved by the Oregon State University Animal Care and Use Committee in accordance with principles outlined by the NIH (14).

    Study design. For 90 d before the study began, the dogs were fed a commercial food (Science Diet Canine Maintenance, Hill's Pet Nutrition) without enhancement of (n-6) and (n-3) FA. The ratio of (n-6) to (n-3) FA in this food was 18:1 (Table 1). The source of (n-3) FA in this food was 90% plant-derived from ALA (soybean oil). Dogs were fed once daily under supervision until all food was consumed; water was consumed ad libitum. Experimental foods (Hill's Pet Nutrition) varied in the amount of (n-3) FA they contained (Tables 1 and 2). For example, in studies 1 and 2, the corn oil–enriched food with low (n-3) FA concentration [0.5 g (n-3) FA/kg of food, wet-weight basis] had a high ratio of (n-6) to (n-3) FA (40.0:1). The fish oil–enriched food with high (n-3) FA concentration [6.2 g (n-3) FA/kg of food, wet-weight basis] had a low ratio of (n-6) to (n-3) FA (1.4:1). The amount of ALA was low in both foods and roughly equivalent.⁶

    Study 2: Do dogs fed the same food over a 36-wk period maintain a stable plasma FA profile? After completing study 1, 10 dogs were fed the same foods that they had received during study 1 for an additional 24 wk. One group (n = 5) consumed the fish oil–enriched food with high (n-3) FA concentration and an (n-6) to (n-3) FA ratio of 1.4:1. The other group (n = 5) consumed the corn oil–enriched food with low (n-3) FA concentration and an (n-6) to (n-3) FA ratio of 40.0:1. Food intake was measured and adjusted to maintain body weight, and blood samples were collected as above from these dogs after they were fed their respective foods for 36 wk.

    Study 3: Do dogs fed foods with the same ratio, but increasing concentrations of (n-6) and (n-3) FA, have similar plasma concentrations of these FA? After completing study 1, the other dogs (n = 22) were reassigned to 4 groups (n = 5 or 6 dogs/group) for the third study. Dogs were given foods with the same ratio of (n-6) to (n-3) FA (1:1) but different concentrations of (n-6) and (n-3) FA. The concentrations of both (n-6) and (n-3) FA in these foods were 3.3 g FA/kg food, 6.3 g FA/kg food, 9.8 g FA/kg food, and 12.4 g FA/kg food (Table 2). All dogs were fed food of the same or higher (n-3) concentration than they had received during study 1. Food intake was measured and adjusted such that dogs did not lose weight. Blood samples were collected as above after the dogs were fed their respective foods for 12 wk.

    Fatty acid analyses. Fatty acid compositions of the experimental foods (Table 1 for studies 1 and 2; Table 2 for study 3) were determined by a commercial laboratory (Eurofins Scientific) by gas chromatography of FA methyl esters. Fatty acid concentration of food is expressed as g FA/kg food as fed. Fatty acid concentration of plasma samples was determined by gas chromatography, as previously described (15), using heptadecanoic acid as the internal standard. Fatty acid concentrations are expressed as g/100 g of FA.⁷

    Statistical analyses. Fatty acid intake [g/(kg body weight · d)], plasma FA (g/100 g FA), and body weights (kg) are reported as means ± SEM. All data were continuous and homoscadastic based on the Kolmogorov-Smirnov Test. For studies 1and 2, a univariate analysis of responses, performed using SAS (SAS/STAT User's Guide, Version 9: SAS Institute), was used to evaluate treatment effects. Also for study 1, a pooled within-treatment correlation between intake and plasma concentrations of DHA, EPA, and total (n-3) FA was conducted using multivariate analysis procedures of SAS (MANOVA/Print E) to establish the E matrix. Study 3 was evaluated using orthogonal polynomials, which were used to assess linear and quadratic trends, using contrast statements in the GLM procedure of SAS. Data were also analyzed using ANOVA with post hoc separation of the means by the LSD post-hoc test. A 2-sample t test was used to compare body weights (pre-, post-, and the difference between pre- and post-treatment body weights) for studies 1 and 2. Body weights for study 3 were analyzed using ANOVA with post hoc separation of the means by the LSD post-hoc test. Overall significance was set at P 0.05.

	Results

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
    Study 1. All dogs readily consumed their respective FA-enriched foods. At the beginning of study 1, dogs fed the high (n-3) FA-enriched food weighed 10.5 ± 0.5 kg. At the end of the study, these dogs weighed 11.7 ± 0.5 kg. At the beginning of study 1, dogs fed the low (n-3) FA-enriched food weighed 11.1 ± 0.5 kg. At the end of the study, these dogs weighed 12.5 ± 0.6 kg. Body weights were not significantly different between groups (pre-, post-, or the difference between pre- and post-treatment body weights), although dogs in both groups weighed more at 12 wk compared with their baseline values (P < 0.001).

There were no differences in selected plasma FA concentrations at baseline before dietary intervention (Table 3). Dogs fed food with high (n-3) FA concentration had higher plasma total (n-3) FA, EPA, and DHA concentrations and lower plasma total (n-6) FA, LA, and AA concentrations than dogs fed the low (n-3) FA food after 12 wk (P < 0.001). The total monounsaturated fatty acid (MUFA) [including 18:1 (n-9)] concentration was higher, but the PUFA concentration and the ratio of (n-6) to (n-3) FA were lower in dogs fed the high (n-3) FA food than in dogs fed the low (n-3) FA food (P < 0.05).

Food intake at the beginning of study 1 for dogs fed the fish oil–enriched food was 110 ± 6 g/(kg body weight · d). Food consumption at the end of study 2 was 78 ± 10 g/(kg body weight · d) (29% decrease), with a mean food intake throughout the 36 wk feeding period of 82 ± 7 g/(kg body weight · d). Food intake at the beginning of study 1 for dogs fed the corn oil–enriched food was 106 ± 7 g/(kg body weight · d). Food consumption at the end of study 2 was 75 ± 9 g/(kg body weight · d) (29% decrease), with a mean food intake throughout the 36 wk feeding period of 84 ± 9 g/(kg body weight · d). Food intake did not differ between the fish oil– and the corn oil–supplemented dogs.

Dogs fed the fish oil–enriched food with high levels of (n-3) FA for 36 wk had lower plasma concentrations of total (n-3) FA, EPA, DHA and total PUFA, and a higher plasma concentration of ALA at 36 wk than at 12 wk (P 0.02; Table 5). Plasma concentrations of 18:1(n-9), total MUFA, 18:2(n-6), 20:4(n-6), and total (n-6) FA at 36 wk did not differ from those at 12 wk. Dogs fed the corn oil–enriched food with low levels of (n-3) FA for 36 wk had higher plasma concentrations of 18:1(n-9), 18:2(n-6), and 18:3(n-3) at 36 wk than at 12 wk, whereas the plasma concentrations of total (n-3) FA and AA were lower at 36 wk than at 12 wk (P 0.03). Plasma concentrations of total MUFA, EPA, DHA, total PUFA, and total (n-6) FA at 36 wk did not differ from the plasma concentrations at 12 wk. Dogs fed both the fish oil– and the corn oil–enriched foods for 36 wk had higher plasma concentrations of SFA at 36 wk than at 12 wk (P = 0.02 and 0.004, respectively).

    Study 3. Four groups of dogs were fed foods with a 1:1 ratio of (n-6) to (n-3) FA, but each food had a different concentration of (n-3) and (n-6) FA. Thus, the doses of (n-3) and (n-6) FA administered/kg body weight were the same for dogs within a group. At the end of the 12-wk feeding trial, the mean body weight for the group of dogs [and change in body weight pre- and post-feeding trial] fed the 3.3 g (n-3) FA/kg food was 14.6 ± 1.2 kg [2.9 ± 0.4]; for dogs fed the 6.3 g (n-3) FA/kg food it was 15.2 ± 1.0 kg [4.2 ± 0.5]; for dogs fed the 9.8 g (n-3) FA/kg food it was 13.0 ± 1.1 kg [1.9 ± 0.5]; and for dogs fed the 12.4 g (n-3) FA/kg food it was 12.2 ± 1.0 kg [1.9 ± 0.5]. Body weights were not significantly different among the groups (pre- or post-feeding trial). Mean food intake throughout the 12-wk feeding trial for the group of dogs fed the 3.3 g (n-3) FA/kg food was 70 ± 9 g/(kg body weight · d); for dogs fed the 6.3 g (n-3) FA/kg food it was 77 ± 11 g/(kg body weight · d); for dogs fed the 9.8 g (n-3) FA/kg food it was 73 ± 9 g/(kg body weight · d); and for dogs fed the 12.4 g (n-3) FA/kg food it was 68 ± 9 g/(kg body weight · d). Food intake was not significantly different among the 4 groups of dogs.

Dogs fed food containing 6.3 g (n-3) and (n-6) FA/kg food had higher plasma concentrations of DHA than dogs fed food containing 3.3 g FA/kg food (P = 0.03), but they had equivalent concentrations with dogs fed food containing 9.8 g FA/kg food (Table 6). For EPA and total (n-3) FA, dogs fed 9.8 g FA/kg food had higher concentrations than those fed food containing 3.3 g FA/kg food (P < 0.05). However, dogs fed food with 12.4 g FA/kg food had plasma concentrations of EPA, DHA, and total (n-3) FA that did not differ from those in dogs fed food containing 3.3 g FA/kg food. Dogs fed food with 3.3 g FA/kg food also had higher plasma concentrations of 18:1 (n-9) and total MUFA (P < 0.001) than dogs fed food with 6.3, 9.8, or 12.4 g FA/kg food (P < 0.05). The g of (n-3) and (n-6) FA consumed/kg food did not affect plasma total (n-6) FA, AA, LA, ALA, total SFA, or total PUFA concentrations.

	Discussion

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 
Therapeutic benefits of dietary supplementation with (n-3) PUFA have been documented in several species, including humans, rodents, and dogs (16–19). Feeding optimal amounts of (n-3) FA to dogs may reduce the incidence of cancer and sudden cardiac death (20–22), and the use of FA supplements has been shown to benefit several pathological conditions, including chronic inflammatory disease, atopy, and chronic renal insufficiency (reviewed in 19). As a result, a variety of foods and FA supplements rich in (n-3) PUFA are currently marketed for use in dogs and cats (23,24). The question remains whether the critical factor in their effectiveness results from the dose of (n-3) FA administered or the dietary ratio of (n-6) to (n-3) FA. Reports indicate a ratio of 5:1 to 10:1 (n-6) to (n-3) FA is the correct dietary ratio; however, experimental data demonstrating the best ratio are scanty and contradictory (25,26). Some studies indicate that both the total PUFA concentration and the ratio of (n-6) to (n-3) FA in the food are important in determining overall effects (27,28). In this study, we found that the dose of (n-3) FA is more important than the dietary ratio of (n-6) to (n-3) FA in affecting the plasma FA profiles in dogs. Furthermore, keeping the dose of (n-3) FA fed constant is fundamental in maintaining plasma levels of EPA, DHA, and total (n-3) FA over long periods of time.

Study 1 was the traditional dietary (n-6) to (n-3) FA ratio study and showed that when an increased concentration of (n-3) PUFA was administered (fish oil– vs. corn oil–enriched food), plasma total (n-3) FA, EPA, and DHA concentrations were increased. More notably, study 1 showed that dogs fed different amounts of food, based on individual variation in food intake needed to maintain body weight, will receive a different dose of (n-3) FA, and those that received the highest dose per kg body weight had the highest plasma DHA concentrations. Thus, the amount of (n-3) FA consumed, independent of the (n-6) to (n-3) FA ratio, was important in determining plasma DHA concentrations.

These findings are underscored in the long-term feeding study 2, whereby food intake was decreased from levels consumed in study 1 to maintain body weights. Even though plasma FA profiles in dogs fed the 2 foods remained significantly different after the 36 wk feeding trial, a change in the dose of (n-3) FA administered over a long period of time resulted in loss of ability to maintain the same plasma FA levels. As a result, dogs fed the fish oil–enriched food for 36 wk had lower plasma concentrations of total (n-3) FA, EPA, and DHA at 36 wk than at 12 wk.

These results are consistent with what we found in a previous study, wherein 3 foods with dietary (n-6) to (n-3) ratios of 31:1, 5.4:1, and 1.4:1 were fed to beagles for 12 wk (1). In that study, the dietary ratio of (n-6) to (n-3) FA affected plasma FA compositions and, consequently, immune system function and eicosanoid metabolism. However, because absolute concentrations of (n-6) and (n-3) FA were different in each of the 3 foods, it was difficult to determine if it was the dose or the dietary ratio of (n-6) to (n-3) FA that had the greater effect on plasma FA composition. Studies supporting both hypotheses exist. For example, a study of rats by Boudreau et al. (29) showed that the ratio of (n-6) to (n-3) PUFA in the food, rather than the absolute amount of (n-3) PUFA, is the major factor suppressing the amount of AA and its metabolites in tissue lipids. Subsequently, a study by Hwang et al. (30) was performed to determine whether the same was true for human beings. Results of this study indicated that it was the absolute amount of fish oil, i.e., dose, and not the relative amounts of fish and vegetable oil, i.e., ratio of (n-6) to (n-3) FA, that determined the magnitude of reduction of AA and increase in EPA in phospholipids of plasma and platelets. In studies 1 and 2, our results could be used to support either dose or dietary ratio of (n-6) to (n-3) FA as the primary determinant affecting plasma FA compositions, because both were varied.

Study 3 was performed to quantify the effect of foods with the same ratio of (n-6) to (n-3) FA, but with increasing concentrations, on plasma FA compositions. This type of experimental design has not, to our knowledge, been previously published for dogs or for humans. Results from study 3 suggested that the absolute dose of (n-3) FA is more important than the (n-6) to (n-3) FA ratio up to a certain food intake level, which appears to be 6.3 g total (n-3) FA and total (n-6) FA/kg food for DHA and 9.8 g FA/kg food for EPA. We hypothesize that, because the (n-3) FA in the fish oil of these diets has a higher percentage of DHA (40%) vs. EPA (30%), it takes a higher intake of total (n-3) FA to maximize plasma EPA concentrations compared with DHA. When the dose of (n-3) and (n-6) FA is increased beyond 9.8 g FA/kg food to 12.4 g FA/kg food, plasma increases in DHA and EPA concentrations are blunted. A significant quadratic response to increasing dietary (n-3) and (n-6) concentrations for plasma DHA and total (n-3) FA also suggests that, as the g (n-3) and matched g (n-6) FA administered/kg body weight increases, there is a maximum effect on plasma DHA concentration, after which plasma levels of DHA return toward baseline. Reasons for this observation are unknown, and future studies with larger group sizes should be conducted to confirm these findings.

Another interesting observation is that the addition of (n-3) FA at any level reduces the relative abundance of (n-6) metabolites, and that there may be a different dose-response of dietary (n-3) FA toward (n-3) related pathways than (n-6) related pathways. In the fish oil–supplemented food of study 1, the concentrations of total (n-3) and total (n-6) were similar to the 6.3 g (n-3) and (n-6) FA/kg food of study 3. However, the plasma AA levels were much lower in dogs fed all of the foods of study 3. Although comparison of the plasma FA concentrations of the 2 studies is confounded by differences in time when the 2 studies were conducted, we suggest that ALA in the food at >0.5 g/kg food (the level present in the corn oil–supplemented food of study 1) inhibits conversion of LA to AA (note the decrease in AA in the fish oil–supplemented dogs of study 1 when ALA was present in the food at 0.6 g/kg food), and that maximal inhibition is present at 0.7 g/kg food (the lowest concentration of ALA in foods of study 3). In the corn oil–supplemented food of study 1, the concentration of total (n-3) FA was very low at 0.5 g/kg food, whereas the concentration of total (n-6) FA was high at 20.0 g/kg food, which resulted in plasma concentrations of LA of 29.6 g/100 g. However, the data from study 3 suggest that the addition of total (n-3) FA at any amount 3.3 g/kg results in a plasma LA of 23 g/100 g. These data show that all concentrations of dietary (n-3) FA result in a reduction of plasma LA.

These findings are noted also in the long-term study 2, whereby food intake was decreased to maintain body weight. In study 2, the fish oil–supplemented food contained 6.2 g (n-3) FA/kg food. When food intake was decreased, dogs fed the fish oil–supplemented food then received less (n-3) FA than needed to maintain plasma DHA and EPA levels, but enough to suppress plasma LA concentrations. Decreased food intake did not decrease ALA intake to the extent needed to alter plasma AA concentrations. Dogs receiving the corn oil–supplemented food also consumed less food and, because the dose of total (n-3) FA was already quite low, decreased consumption resulted in plasma total (n-3) FA being even lower at 36 wk, and consequently plasma LA was higher.

The concept of the (n-6) to (n-3) ratio evolved from early rodent studies wherein LA and ALA were the only 2 variables; under such conditions, one can find support for the importance of the ratio as well as the amounts of these fatty acids consumed (29,31). For example, there are studies showing that if the (n-3) intake as ALA is fixed, the subsequent rise in blood EPA is usually higher with a low (n-6) intake as LA than with very high intakes of LA (32). We did not fix ALA intake and change the LA intake in the absence of the long chain (n-3) FA, EPA and DHA. Our experimental design, which includes the long-chain (n-3) FA as EPA and DHA, is quite different from the aforementioned studies wherein EPA and DHA did not contribute to the (n-6) to (n-3) ratio. Also, whether our results would be the same had the (n-6) metabolite AA been fed directly, rather than as the precursor LA, remains to be determined in future studies. We chose fish oil– and corn oil–supplemented foods because these oils are currently included in dog foods.

A selectivity favoring the highly unsaturated fatty acids for esterification into phospholipids makes them more abundant in phosphoglycerides than in triacylglycerols and makes analysis of phospholipids a preferred approach to evaluating tissue highly unsaturated FA contents (33). An indication of the extent of dietary exposure to LA and ALA is provided by analyses of the plasma triacylglycerols, whereas the internal exposure of tissues to the highly unsaturated FA is provided by analyses of plasma phospholipids (33). We did not fractionate plasma lipids into subclasses prior to analysis.

Our results, which show an effect of dose rather than dietary ratio of (n-6) to (n-3) FA on plasma FA concentrations, have important implications for determining the desired amount of (n-3) FA needed in canine foods to maximize plasma FA concentrations. Dogs fed food with 3.3, 6.3, 9.8, and 12.4 g (n-3) and g (n-6) FA/kg food received a mean dose of 0.23, 0.44, 0.73, and 0.86 g (n-3) and g (n-6) FA/kg body weight, respectively. Results from our studies indicate that 440 mg (n-3) FA/(kg body weight · d) is required to maximize plasma levels of DHA. Bauer et al. (13) showed that dietary energy influenced their relations. Because our experiments were designed with foods that changed FA concentration and energy together, it is not possible to evaluate that relation with these data. Our analysis was completed expressing intake per kg of body weight; results were similar when food intake was expressed per unit metabolic size. Within the constraints of our design, the maximal response of DHA occurs at 175 mg/kg body weight. Surveys of multiple brands of commercial dog foods show that dietary (n-3) FA intake ranges from 16 to 283 mg/(kg body weight · d), and dietary (n-6) FA intake ranges from 168 to 938 mg/(kg body weight · d), depending on the brand of food (23,24). Based on these surveys, we can say with limited exceptions (Prescription Diet n/d canned; Prescription Diet j/d, canned and dry; and Prescription Diet d/d Salmon Formula canned), that commercial foods do not have the concentrations of DHA needed to maximize plasma levels of DHA. Further studies are required to determine the minimum and maximum intake of (n-3) FA necessary to exert favorable results relevant to specific diseases.

	FOOTNOTES

 
¹ Supported in part by a grant from Hill's Pet Nutrition, Inc, P.O. Box 1658, Topeka, KS 66601-1658.

⁵ Abbreviations used: AA, arachidonic acid; ALA, -linolenic acid; DHA, docosahexaenoic acid; DTH, delayed-type hypersensitivity; EPA, eicosapentaenoic acid; FA, fatty acids; LA, linoleic acid; LT, leukotriene; MUFA, monounsaturated fatty acids; PG, prostaglandin.

⁶ The basal food ingredients (by weight) included 54.8% water, 20.3% turkey, 15.0% corn, 4.5% pork liver, 2.0% soy meal, 1.0% beet pulp, and 0.4% vitamin and mineral premixes. Rice hulls were used as the carrier for the vitamin premix, which contained 25 mg/kg cholecalciferol, 7.5 g/kg nictotinic acid, 5 g/kg calcium D-pantothenate, 21.8 g/kg thiamine mononitrate, 1.25 g/kg riboflavin, 2.43 g/kg pyridoxine hydrochloride, 250 mg/kg folic acid, 50 mg/kg biotin and 50 mg/kg vitamin B-12. Calcium carbonate was used as the carrier for the mineral mix, which contained 80 g/kg zinc as zinc oxide, 6.0 g/kg manganese as manganese oxide, 280 g/kg iodine as calcium iodate, 1.0 g/kg cobalt as cobalt carbonate, 180 mg/kg selenium as selenium selenite, and 2.5 g/kg copper as copper chloride. The basal diet contained 2.5% fat (27 energy % fat). The remaining 2% of the food was provided as added oil. The source of oil for the (n-3) enriched food was Menhaden fish oil (Zapata Protein); the source of oil for the (n-6) enriched food was Mazola corn oil. Foods were analyzed at a commercial laboratory (Woodson-Tenent Laboratories). Nutrient composition (by weight) was 77.4% moisture, 5.8% protein, 4.5% fat (40 energy % fat), 1.3% ash, 0.7% crude fiber, and 10.3% carbohydrate.

⁷ Sum of the SFA was determined as follows: 8:0 + 10:0 + 11:0 + 12:0 + 14:0 + 15:0 + 16:0 + 17:0 + 18:0 + 20:0 + 22:0 + 24:0. Sum of the MUFA was determined as follows: 14:1 + 15:1 + 16:1 (n-7) + 17:1 + 18:1 (n-9)c + 18:1 (n-7) + 18:1 (n-9)t + 20:1 (n-9) + 22:1 (n-9) + 24:1. Sum of the PUFA was determined as follows: 18:2 (n-6) + 18:3 (n-6) + 18:3 (n-3) + 18:4 (n-3) + 20:2 (n-6) + 20:3 (n-6) + 20:3 (n-3) + 20:4 (n-6) + 20:4 (n-3) + 20:5 (n-3) + 21:5 (n-3) + 22:2 (n-6) + 22:4 (n-6) + 22:5 (n-6) + 22:5 (n-3) + 22:6 (n-3).

Manuscript received 6 March 2006. Initial review completed 28 March 2006. Revision accepted 13 June 2006.

	LITERATURE CITED

TOP ABSTRACT Introduction Materials and Methods Results Discussion LITERATURE CITED

 

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