This prospective study involved supplementing 18 normal dogs with flax seed (FLX) and sunflower seed (SUN) and evaluating their effects on skin and hair coat condition scores and serum polyunsaturated fatty acids (PUFA) concentrations. Skin and hair coat were evaluated in a double-blinded fashion using a numeric scoring system and serum PUFA concentrations were determined. Our hypothesis was that changes in serum PUFA concentrations are associated with improvements in skin and hair coat and that serum PUFA would provide an objective method for making dietary fatty acid supplement recommendations. Although a numerical improvement was found in hair coat quality in both groups, this improvement was not sustained beyond 28 days. The relative per cent of 18:3n-3 concentrations in serum phospholipids increased in the FLX treated dogs but these concentrations remained unchanged in the SUN treated dogs. Also, elevations in relative per cent of 18:2n-6 concentrations in serum phospholipids were seen in the FLX group. The ratio of serum polyunsaturated to saturated fatty acids also showed a transient increase. These increases preceded the peak skin condition score peak value by approximately 14 days. It was concluded that a 1-month supplementation with either flax seed or sunflower seed in dogs provides temporary improvement in skin and hair coat. These changes appeared to be associated with increased serum 18 carbon PUFA.

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A study was conducted in dogs to assess n-3 long chain polyunsaturated fatty acid incorporation after feeding an alpha-linolenic (ALA)-rich flaxseed supplemented diet (FLX) for 84 days. Serum total phospholipids (PL), triacylglycerol (TG), and cholesteryl esters (CE) were isolated at selected times and fatty acid methyl esters were analyzed. Increased LA was seen in the FLX-PL fraction after 28 days and an expected decrease in PL-AA. Enrichment of ALA, eicosapentaenoic acid (EPA) and docosapentaenoic acid n-3 (DPAn-3) in the FLX-group occurred early on (day 4) in both PL and TG fractions but no docosahexaenoic acid (DHA) was found, consistent with data from other species including humans. In contrast, no accumulation of DPAn-3 was seen in serum-CE, suggesting that this fatty acid does not participate in reverse-cholesterol transport. The accumulation of DPAn-3 in fasting PL and TG fractions is likely due to post-absorptive secretion after tissue synthesis. Because conversion of DPAn-3 to DHA occurs in canine neurologic tissues, this DPAn-3 may provide a circulating reservoir for DHA synthesis in such tissues. The absence of DPAn-3 in serum-CE suggests that such transport may be unidirectional. Although conversion of DPAn-3 to DHA is slow in most species, one-way transport of DPAn-3 in the circulation may help conserve this fatty acid as a substrate for DHA synthesis in brain and retinal tissues especially when dietary intakes of DHA are low.

EXPANDED ABSTRACT [18:3(n-3), ALA] are converted to long-chain polyunsaturated fatty acids (LCPUFAs) by desaturase and chain-elongation enzyme systems (1). The LCPUFAs are important because they serve as eicosanoid precursors. In addition, several LCPUFAs have specific structural and functional roles in development or maintenance of neural tissues such as brain, retina and other tissues (2).The rate-limiting step for desaturation and elongation is controlled by ⌬6-desaturase, which adds a double bond at the sixth carbonyl carbon. Hence, LA is converted to 18:3(n-6) and ALA is converted to 18:4(n-3) and competition between these substrates for this enzymatic step exists among the fatty acid families. Some reports indicate a higher specificity for (n-3) fatty acid desaturation compared to that for (n-6) fatty acids (3).Dogs are important to humans not only as companion animals but also serve as a model for human metabolism (4,5). This study addresses EFA metabolism in dogs using a classical enzyme kinetic approach. MATERIALS AND METHODS AnimalsFresh liver tissues were removed from 11 normal, healthy Coonhound dogs and three Sprague-Dawley rats at the termination of animal use protocols approved by Texas A&M University Laboratory Animal Use Committee. The animals had been fed once daily and were not denied food before euthanasia. Liver microsomes were prepared with rat serving as a positive control group for enzyme activity determinations. Microsomal preparationLiver tissue was immediately transferred to ice-cold saline after collection, blotted dry, minced and rinsed twice with saline. A phosphate buffer (40 mM, Buffer A) containing 0.1 M sucrose (pH 7.4) with tissue-to-buffer ratio of 1:6 was used for homogenization. Homogenates were centrifuged for 20 min at 4°C and 10,000 ϫ g with fixed-angle rotor. Supernates were then centrifuged for 1 h at 4°C and 105,000 ϫ g to pellet the microsomes. Microsomes were resuspended in fresh Buffer A and protein concentrations determined before freezing at Ϫ80°C. Microsomal lipid composition determinationMicrosomes were extracted by the method of Folch et al. (6) with internal standards for phospholipids (PL), nonesterified fatty acids (FFA) and triacylglyerol (TG) containing 22:1(n-9). Lipid subclasses were separated by thin-layer chromatography (TLC) on silica gel plates with 80:20:1 hexane:ether:glacial acetic acid (v/v/v). The PL, FFA and TG were scraped and fatty acid methyl esters (FAME) prepared. Samples were quantified by capillary gas chromatography (GC) on a Restek Stabilwax column (0.32 mm ID ϫ 30 m ϫ 0.25 mm film) with He gas carrier. A temperature program was begun at 170°C, held for 10 min, ramped to 228°C at 2°C/min then held for 20 min. IncubationsIncubation conditions for ALA as substrate in the absence of malonyl-CoA were determined by independently varying C 14 -ALA or C 14 -LA substrate content, protein concentrations and incubation times. Protein (4 mg), 15-min incubation and 50 M ALA substrate concentration were found to be suitable conditions for ⌬6-desatu...

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