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Identifying dietary effects on appetite-regulating hormones will enhance our understanding of appetite control. Before complex diets are tested, effects of specific macronutrients or feeding frequency should be identified. The objectives of this nutrition study were to identify differences in endocrine response with feeding frequency (Exp. 1) and after a single dose of a sole macronutrient (Exp. 2). A control diet supplying similar energy content from carbohydrate, protein, and fat was fed to maintain ideal BW. In Exp. 1, 8 healthy adult (1.9 [+ or -] 0.1 yr old) female hound cross dogs with an average BW of 22 kg (4.8 [+ or -] 0.8 BCS based on a 9-point scale) were randomly allotted to 1 of 2 treatments (fed once or twice daily) in a crossover design. After a 14-d adaptation period, a blood sample was taken (10 mL) before feeding, and samples were collected every 2 h postprandially for 24 h. In Exp. 2, dogs were randomly allotted to 1 of 4 treatments in a 4 x 4 Latin square design. After a 6-d adaptation period, the normal meal on d 7 was replaced with a bolus of maltodextrin (50 g in water; CARB), canned chicken (50 g; PROT), lard (25 g; fat), or water (200 mL). A blood sample (10 mL) was taken at 0, 30, 60, 90, 120, 150, 180, 240, 300, and 360 min postprandial. Total ghrelin, active glucagon-like peptide-1 (GLP-1), insulin, and glucose concentrations were measured. Data were analyzed to compare changes from baseline and area under the curve (AUC) among treatments. In Exp. 1, all hormones were quite variable throughout the day, with a few insulin and GLP-1 differences because of feeding frequency. In Exp. 2, CARB produced a marked peak in glucose and insulin concentrations compared with PROT, fat, or water, resulting in increased glucose (P < 0.001) and insulin (P = 0.07) incremental AUC values. On the other hand, the fat treatment led to increased GLP-1 concentrations over time. Ghrelin AUC was not different among treatments. The circulating hormone data were highly variable and indicate that diet plays a role in insulin and GLP-1 secretion, but more research is required to elucidate these effects. Key words: appetite, dog, ghrelin, glucagon-like peptide, macronutrient doi: 10.2527/jas.2010-2938

Meat and fish serve as important protein sources in the companion animal diet; however, limited protein digestibility data are available for assessing protein digestibility differences among good-quality protein sources. Beef loin, pork loin, chicken breast, pollock fillet, and salmon fillet were evaluated for composition, protein digestibility, and AA bioavailability using the immobilized digestive enzyme assay, cecectomized rooster assay, and ileally cannulated dog assay. Pollock contained the greatest amount of CP, total essential AA (TEAA), and total nonessential AA (TNEAA; DM basis; 96.9, 38.6, and 50.3%, respectively). Salmon contained the next greatest amounts (92.8, 36.4, and 44.6%), followed by chicken (90.3, 36.1, 43.2%). Beef had the least CP content (82.7%), but had slightly greater TEAA and TNEAA concentrations (33.9, 42.0%) compared with pork (86.2, 33.6, 41.3%). Immobilized digestive enzyme assay values were greatest for pollock fillet (0.71) and least for chicken breast (0.52). Beef loin, pork loin, and salmon fillet were similar (0.63, 0.62, and 0.64, respectively). Standardized TEAA and TNEAA digestibility coefficients, evaluated using the cecectomized rooster assay, were greatest (P < 0.05) for pollock fillet (90.4 and 89.8%, respectively) and least (P < 0.05) for chicken breast (86.6 and 85.9%, respectively) and salmon fillet (87.8 and 86.4%, respectively). Dogs assigned to a 5 x 5 Latin square design were fed 5 diets, with each test substrate as the major protein source. No significant differences (P > 0.05) were found in ileal digestibility of protein. Values ranged from 88.9% for chicken to 90.5% for pork loin and pollock fillet. Ileal TEAA and TNEAA coefficients were not different among test substrates, with values between 91.7 and 92.7%, and 88.8 and 90.4%, respectively. Total tract CP apparent digestibility values ranged from 94.4 to 94.8%, with no differences noted among treatments. Despite marked differences in composition and predicted and standardized digestibility values, when the protein sources were added to diets at a concentration of approximately 30% (25% of total energy intake), no differences in test protein substrates were noted in either ileal or total tract nutrient digestibility. Key words: amino acid bioavailability, animal protein, canine, digestibility, fish doi: 10.2527/jas.2009-2140

The competitive dynamics between domestic and native carnivores are poorly studied. We examined competition for food between sympatric populations of free-ranging dogs (Canis familiaris) and Indian foxes (Vulpes bengalensis) through dietary analysis in a protected, dry grassland habitat in central India. We expected significant dietary overlap between dogs and foxes because of clear evidence of interference competition between dogs and foxes in this area. However, dogs subsisted largely on human-derived foods (HDFs) from direct feeding, and scavenging on garbage, crop residue, and livestock carcasses (83% relative occurrence [RO]). Wild-caught foods constituted only 11% RO of the diet of dogs. The majority of the diet of Indian foxes consisted of invertebrates (33% RO), rodents (20% RO), and fruits of Zizyphus (18.5% RO). Indian foxes did not consume HDF, nor did they scavenge from large-mammal carcasses, and included only a small portion of agricultural produce in their diet. The low contribution of HDF and agricultural food sources to the diet of Indian foxes was surprising because this species is a generalist omnivore. Dogs may be preventing foxes from accessing agricultural lands and human-associated foods by interference competition. Key words: Canis familiaris, dietary overlap, human-derived food, interference competition, Vulpes bengalensis

Five ileal-cannulated adult dogs were utilized in a 5 x 5 Latin square design to determine the effects of fructan type and concentration on nutrient digestibility, stool metabolite concentrations, and fecal microbiota. Five diets were evaluated that contained cellulose alone or with inulin or short-chain fructooligosaccharides (scFOS) each at 0.2 or 0.4% of the diet. Dogs were fed 175 g of their assigned diet twice daily. Chromic oxide served as a digestibility marker. Nutrient digestibility; ileal and fecal pH and ammonia concentrations; ileal IgA concentrations; and fecal short- and branched-chain fatty acid concentrations, microbiota, and concentrations of phenol, indole, and biogenic amines were measured. No differences were observed in ileal pH or ammonia or fecal concentrations of indole or valerate. Ileal DM, OM, and CP digestibility coefficients; total tract DM and OM digestibility coefficients; and fecal concentrations of phenylethylamine increased linearly (P < 0.05), and fecal concentrations of phenol decreased linearly (P < 0.05) with inulin supplementation. Fecal concentrations of acetate, propionate, and total short-chain fatty acids decreased quadratically (P < 0.05) with inulin supplementation. Ileal DM, OM, and CP digestibility coefficients increased linearly (P < 0.05), and fecal phenol concentration decreased linearly (P < 0.05) with seFOS supplementation. Total tract DM and OM digestibility coefficients as well as fecal butyrate and isobutyrate concentrations increased quadratically (P < 0.05) with scFOS supplementation. Although a greater level of inclusion is needed to modify gut microbiota populations, low-level inclusion of inulin or seFOS is effective in modifying key nutritional outcomes in the dog. Key words: dog, fructan, microbiota, nutrient digestibility, phenols, protein catabolite

Dogs (Canis familiaris) trained to receive a preferred food (dry beef liver) from an experimenter learned to maintain a longer gaze on the experimenter than dogs receiving a less preferred food (dog pellets). Dogs downshifted from dry liver to pellets rejected food more frequently than nonshifted controls. Gaze duration also decreased in downshifted dogs below the level of a group always reinforced with pellets. In addition, downshifted dogs tended to move away from the experimenter, adopting a lying down posture. This phenomenon, called successive negative contrast, has been described in analogous experiments with a variety of mammalian species, but has failed to occur in similar experiments with nonmammalian vertebrates. Unlike similar previous observations, the present data were obtained in an environment involving interspecific communication. Keywords: incentive contrast, frustration, interspecific communication, domestic dogs

The current study aimed to evaluate the variation in fermentation activity along the distal canine gastrointestinal tract (GIT, Exp. 1). It also aimed to assess fermentation kinetics and end product profiles of 16 dietary fibers for dog foods using canine fecal inoculum (Exp. 2). For Exp. 1, digesta were collected from the distal ileum, proximal colon, transverse colon, and rectum of 3 adult dogs. Digesta per part of the GIT were pooled for 3 dogs, diluted (1:25, wt/vol), mixed, and filtered for the preparation of inoculum. A fructan, ground soy hulls, and native potato starch were used as substrates and incubated for cumulative gas production measurement as an indicator of the kinetics of fermentation. In addition, fermentation bottles with similar contents were incubated but were allowed to release their gas throughout incubation. Fermentation fluid was sampled at 4, 8, 12, 24, 48, and 72 h after initiation of incubation, and short-chain fatty acids and ammonia were measured. Results showed comparable maximal fermentation rates for rectal and proximal colonic inocula (P > 0.05). Production of short-chain fatty acids was least for the ileal and greatest for the rectal inoculum (P < 0.05). Therefore, for in vitro studies, fecal microbiota can be used as an inoculum source but may slightly overestimate in vivo fermentation. Experiment 2 evaluated the gas production, fermentation kinetics, and end product profiles at 8 and 72 h of incubation for citrus pectin, 3 fructans, gum arabic, 3 guar gums, pea fiber, peanut hulls, soy fiber, sugar beet fiber, sugar beet pectin, sugar beet pulp, wheat fiber, and wheat middlings. Feces of 4 adult dogs were used as an inoculum source. Similar techniques were used as in Exp. 1 except for the dilution factor used (1:10, wt/vol). Among substrates, large variations in fermentation kinetics and end product profiles were noted. Sugar beet pectin, the fructans, and the gums were rapidly fermentable, indicated by a greater maximal rate of gas production ([R.sub.max]) compared with all other substrates (P < 0.05), whereas peanut hulls and wheat fiber were poorly fermentable, indicated by the least amount of gas produced (P < 0.05). Sugar beet fiber, sugar beet pulp, soy fiber, and wheat middlings were moderately fermentable with a low [R.sub.max]. Citrus pectin and pea fiber showed a similar low [R.sub.max], but time at which this occurred was later compared with sugar beet fiber, sugar beet pulp, soy fiber, and wheat middlings (P < 0.05). Results of this study can be used to formulate canine diets that stimulate dietary fiber fermentation along the distal GIT that may optimize GIT health and stimulate the level of satiety in dogs. Key words: dog, fiber, in vitro fermentation kinetics, short-chain fatty acid

Dietary fibers may modulate insulin resistance and glucose homeostasis in dogs. Their efficacy is, however, dependent on their origin, physical properties, and fermentability in the large bowel. Eight healthy Beagle dogs were fed a commercial diet at twice their maintenance requirements until they became obese. They were then maintained in the obese state and used in a cross-over design study to evaluate the effects of short-chain fructooligosaccharide (scFOS) supplementation (1% wt:wt dry matter in the diet). The euglycemic hyperinsulinemic clamp technique was performed before and after fattening and at the end of each 6-wk cross-over period. Fat tissue biopsies were taken in food-deprived and postprandial phases to measure mRNA abundance of genes involved with fatty acid, glucose metabolism, or inflammation. Insulin resistance appeared progressively with fattening and the rate of glucose infusion during euglycemic clamp was lower (P < 0.05) at the end of the fattening period (7.39 mg x [kg.sup.-1] x [min.sup.-1]) than at baseline (21.21 mg x [kg.sup.-1] x [min.sup.-1]), in stable obese dogs, scFOS increased (P < 0.05) the rate of glucose infusion compared with control (7.77 vs. 4.72 mg x [kg.sup.-1] x [min.sup.-1]). Plasma insulin and triglyceride concentrations were greater in obese than in lean dogs but were not altered by scFOS. Whereas mRNA was not affected in food-deprived dogs, scFOS increased uncoupling protein 2 (P = 0.05) and tended to increase carnitine palmitoyl transferase 1 adipose mRNA levels during the postprandial period (P = 0.09). Adding 1% scFOS to the diet of obese dogs decreases insulin resistance and appears to modulate the transcription of genes involved in fatty acid or glucose metabolism.

Blends of fermentable oligosaccharides in combination with nonfermentable fiber, cellulose, were evaluated for their ability to serve as dietary fibers in dog foods. Using a 6 x 6 Latin square design, 6 diets were evaluated that contained either no supplemental fiber, beet pulp, cellulose, or blends of cellulose, fructooligosaccharides, and yeast cell wall added at 2.5% of the diet. Six ileal-cannulated dogs were fed 175 g of their assigned diet twice daily. Chromic oxide served as a digestibility marker. Nutrient digestibility, fecal microbial populations, fermentative end products, and immunological indices were measured. Total tract DM and OM digestibilities were lowest (P < 0.05) for the cellulose treatment. Crude protein digestibility was lower (P < 0.05) for the treatments containing carbohydrate blends. The cellulose treatment had the lowest (P < 0.05) concentration of bacteria, and all diets containing fermentable fiber had greater (P < 0.05) fecal bifidobacteria concentrations compared with the diets without supplemental fermentable fiber. Lactobacilli concentrations tended to be greater (P < 0.08) in treatments containing fermentable fiber compared with the cellulose treatment. Bifidobacteria and lactobacilli concentrations were similar for the beet pulp treatment compared with the fermentable oligosaccharide blends. Total fecal short-chain fatty acid concentration was greater for the beet pulp treatment (P < 0.05) compared with the control and cellulose treatments. The treatments containing fermentable fiber had greater (P < 0.05) fecal butyrate concentrations compared with cellulose and control treatments. Immune indices were not affected by treatment. Our results suggest that dog foods containing blends of fermentable and nonfermentable carbohydrates produce similar physiological results as dog food containing beet pulp as a fiber source. Therefore, blends of these carbohydrates could be useful substitutes for beet pulp in dog foods. Key words: beet pulp, dietary fiber, dog, intestinal microbiota, oligosaccharide

The idea of cooking for my dogs turns me pale. Not because I think there's anything wrong with cooked diets, or because I'm worried about doing it right, but for [...]

Osteoarthritis is the number one cause of chronic pain in dogs, affecting one in five adult dogs, with the incidence more than doubling in dogs seven years and older. It [...]

How should you choose a canned food for your dog? To start, by looking past its advertising in dog magazines or its front label. We suggest you focus on its [...]

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) ks required to attain maximum plasma levels of DHA.

What could be better than curing your dog's cancer? That's easy! How about avoiding the illness in the first place? No one has done any clinical trials or statistical studies [...]

Last month, in 'A Super (But Secret) Industry,' I discussed the difficulty of getting into a factory where wet pet food is made--a task I have not yet managed to [...]

Cancer always sounds like a death sentence, no matter how the diagnosis is delivered. When patients are cured, they're the exception rather than the rule--especially when they are very young [...]

We determined whether intraportal caffeine infusion, at rates designed to create concentrations similar to that seen with normal dietary intake, would enhance net hepatic glucose uptake (NHGU) during a glucose load. Dogs (n = 15) were implanted with sampling and infusion catheters as well as flow probes >16 d before the studies. After a basal sampling period, dogs were administered a somatostatin infusion (0-150 min) as well as intraportal infusions of glucose [18 [micro]mol/ (kg- min)], basal glucagon [0.5 ng/(kg, min)], and insulin [8.3 pmol/ (kg * min)] to establish mild hyperinsulinemia. Arterial glucose was clamped at 10 mmol/L with a peripheral glucose infusion. At 80 min, either saline (Control; n = 7) or caffeine [1.5 [micro]mol/(kg * min); n = 8] was infused into the portal vein. Arterial insulin, glucagon, norepinephrine, and glucose did not differ between groups. In dogs infused with caffeine, NHGU was significantly higher than in controls [21.2 [+ or -] 4.3 vs. 11.2 [+ or -] 1.6 [micro]mol/(kg * min)]. Caffeine increased net hepatic lactate output compared with controls [12.5 [+ or -] 3.8 vs. 5.5 [+ or -] 1.5 [micro]mol/(kg * min)]. These findings indicate that physiologic circulating levels of caffeine can enhance NHGU during a glucose load, and the added glucose consumed by the liver is in part converted to lactate. KEY WORDS: * glycogen * coffee * carbohydrate * methylxanthines

In this experiment, three concentrations (0.3, 0.6, and 0.9% of diet, as-fed basis) of two fructans, oligofructose (OF) and inulin, were tested against a 0% supplemental fructan control. Seven ilealcannulated adult female dogs were fed a meat-based, kibbled diet and assigned to treatments in a 7 x 7 Latin square design. Dietary supplementation of fructans had no effect on nutrient intakes or ileal digestibilities. Total-tract digestibilities of DM, OM, and CP decreased (P < 0.05) as a result of dietary OF and inulin supplementation. Dogs fed the control diet had a DM totaltract digestibility of 83.0%. The percentages of fecal DM for dogs fed the control and 0.3, 0.6, and 0.9% OF were 36.6, 33.3, 32.8, and 31.7%, respectively. When compared with the control, OF (P < 0.01) and inulin (P < 0.01) supplementation increased fecal ammonia concentrations. Higher fecal short-chain fatty acid (SCFA; P < 0.10) and isovalerate concentrations (P < 0.01) were noted for dogs fed both fructans. Total fecal SCFA for dogs fed the control diet and 0.3, 0.6, and 0.9% OF were 406.4, 529.9, 538.3, and 568.8 [micro]mol/g of feces (DM basis), respectively. Dogs fed 0.3, 0.6, and 0.9% inulin had total fecal SCFA of 472.2, 468.8, and 471.5 [micro]mol/g of feces (DM basis), respectively. Linear increases were observed in putrescine (P < 0.11), cadaverine (P < 0.07), spermidine (P < 0.12), and total amines (P < 0.05) in feces of dogs fed OF. Lower fecal phenol (P < 0.08) and total phenol (P < 0.04) concentrations occurred in dogs fed inulin, along with a linear decrease (P < 0.08) in total phenols with OF supplementation. Total fecal phenols for dogs fed the control, 0.3, 0.6, and 0.9% inulin were 3.03, 1.86, 1.97, and 2.23 [micro]mol/ g of feces (DM basis), respectively. Low-level dietary inclusion of inulin and OF positively affected indices known to be associated with gut health of the dog without seriously compromising nutrient digestibility or stool quality. Overall, the 0.9% OF treatment resulted in the best responses, including no adverse effect on nutrient intakes, ileal digestibilities, or stool quality, as well as increased fecal SCFA and decreased fecal phenols. The biological responses due to inulin were more variable. Key Words: Dogs, Fructans, Inulin, Nutrient Digestibility, Oligofructose, Protein Catabolites

Labrador retrievers (42 of original 48) were used to assess the effects of lifetime diet restriction on glucose tolerance at ages 9-12 y. Restricted-fed (RF) dogs were fed 75% of the same diet consumed by control-fed (CF) pair-mates. An intravenous glucose tolerance test was done annually (maximal stimulation, nonsteady-state). Diet treatment, age, and interactions were fixed effects. Statistical procedures used included mixed-model, repeated-measures ANOVA; least-squares means; Tukey's multiple comparison; paired t tests; and Spearman rank correlations. Glucose k-value and half-life, and insulin sensitivity (total, and 9, 10, 11 y, and per lean mass) were higher (P < 0.05) in RF than in CF dogs. Late-phase insulin release [area under the curve (AUC) 30-120 min] was less (P < 0.05) in RF than in CR dogs. Early-phase insulin release (AUC 0-5 min), y 12 insulin sensitivity and insulinogenic index did not differ between RF and CF dogs. Insulin peak, [DELTA] and total AUC increased (P < 0.05) with age, whereas the glucose k-value and glucose half-life were not affected by age. Insulin sensitivity was negatively, and insulin AUC 30-120 min, peak and [DELTA] glucose were positively correlated with body weight, body condition score, fat mass, percentage of fat and abdominal fat/total tissue. Higher insulinogenic indices tended (P = 0.053) to be associated with greater median survival and dogs with higher insulin sensitivity were at lower (P 0.05) risk of dying or receiving chronic disease treatment. Time to first osteoarthritis treatment or death was greater with lower basal glucose and higher insulin sensitivity (P < 0.05), but diet restriction explained most of this relationship's variation. Glucose disposal efficiency and insulin response were associated with increased quality and length of life in diet-restricted dogs. KEY WORDS: * diet restriction * glucose tolerance * insulin sensitivity * chronic disease * dogs

Eight mature female dogs (18.0[+ or -]0.2 kg) were used in a replicated 4 x 4 Latin square experiment to determine the feeding value of low-ash poultry meal (PM) in a complete food fed to dogs. All foods contained graded concentrations of PM (10.4 to 32.5% DM), resulting in foods that were 10, 15, 20, and 25% CP. Daily DMI averaged 284[+ or -]14 g/d. An increase in PM resulted in an increase in fecal moisture from 44.7 to 55.1% (linear; P < 0.01), and fecal DM output increased from 24.8 to 31.6 g/d (linear; P < 0.05). Ileal DM flow increased from 27.1 to 40.7 g/d (linear; P < 0.01). Small intestinal DM digestibility decreased from 90.4 to 86.1% (linear; P < 0.01) and total-tract DM digestibility decreased from 91.2 to 89.4% (linear; P < 0.01) as PM increased. Large intestinal DM digestibility increased from 8.4 to 21.1% with increasing PM (linear; P < 0.05). Fecal excretion of CP increased from 5.6 to 10.0 g/d (linear; P < 0.01) and ileal flow of CP increased from 6.9 to 15.6 g/d (linear; P < 0.01) as PM increased. Small intestinal CP digestibility was unaffected with treatment (P > 0.05). Large intestinal CP digestibility increased from 21.6 to 37.1% (linear; P < 0.05) with increasing PM. Total-tract CP digestibility increased from 81.0 to 86.6% (linear; P < 0.01) as PM increased. Arginine had the highest overall digestibility ranging from 88.5 to 91.3%, whereas cysteine had the lowest digestibility, ranging from 67.1 to 71.4%. These data indicate that PM is a highly digestible protein source for canine foods with inclusions of 10.4 to 32.5% of DM. Key Words: Amino Acids, Ash, Digestibility, Dogs

The cysteine proteinases, [micro]- and m-calpain, along with their inhibitor, calpastatin, have been hypothesized to play a role in skeletal muscle protein degradation. Because nutrition has previously been shown to influence the expression of calpastatin, the working hypothesis of this study was that the quantity and source of dietary protein could influence regulation of the calpain system in muscle. The objectives to support this hypothesis were to determine the effects of dietary protein (amount and source) on the expression of calpastatin in canine skeletal muscle. This study comprised eight diets with seven dogs per diet. A biopsy was taken from the biceps femoris of all 56 dogs before and after 10 wk on their respective diets. This experimental design allowed examination of change within individual dogs. Diets 1 to 4 contained 12% total protein derived from chicken and/or corn gluten meal in ratios of 100:0, 67:33, 33:67, and 0:100%, respectively. Diets 5 to 8 contained 28% total protein with protein sources and ratios identical to Diets 1 to 4. Differences in calpastatin were examined qualitatively using SDS-PAGE and immunoblotting, and semiquantitatively with densitometric analyses. The majority of the calpastatin blots showed three distinct calpastatin bands, the uppermost appearing at approximately 110 kDa. Diet 5 (28% CP, 100% chicken) resulted in an increase in the expression of the 110-kDa calpastatin band compared with the other two lower molecular weight bands in the same samples. Muscle from dogs fed Diet 5 showed greater increase in (P < 0.05) calpastatin intensity of the topmost band than those fed Diet 8 (0:100; chicken:corn gluten meal). Diet 5 (100:0; chicken:corn gluten meal) showed greater total calpastatin intensity than Diet 8 (0:100; chicken: corn gluten meal). These data suggest that dogs fed a diet containing a higher total percentage of chicken protein may have a greater potential to regulate calpain-mediated degradation of muscle protein than dogs fed diets containing corn gluten meal. Key Words: Dogs, Dietary Protein, Proteinases, Skeletal Muscle

Fructans are fermentable carbohydrates and include short-chain fructooligosaccharides (scFOS), inulin, and hydrolyzed inulin (oligofructose, OF). Two studies with dogs were designed to examine the effects of low concentrations of fructans on nutrient digestibilities, fecal microbial populations, and endproducts of protein fermentation, and fecal characteristics. In Exp. 1, 11 adult male beagles were fed corn-based, kibbled diets supplemented with or without OF to provide 1.9 [+ or -] 0.6 g/d. Dietary inclusion of OF decreased (P < 0.05) nutrient digestibilities, but did not affect fecal characteristics. Increasing OF concentration tended (P < 0.06) to linearly decrease fecal ammonia concentrations, but not those of branched-chain fatty acids (BCFA), amines, indole, or phenols. Fecal concentrations of total short-chain fatty acids (SCFA) and butyrate tended to be higher in OF-supplemented dogs (P < 0.10), as was the ratio of bifidobacteria to total anaerobes (P = 0.15). In Exp. 2, ileally cannulated adult female hounds were fed a meat-based kibbled diet and were assigned to four scFOS treatments (0, 1, 2, or 3 g/d) in a 4 x 4 Latin square design. Ileal nutrient digestibilities tended to increase (P < 0.15) with increasing concentrations of scFOS. On a DMI basis, fecal output tended to decrease linearly (P < 0.10) in response to increasing scFOS supplementation, whereas fecal score tended to exhibit a quadratic response (P = 0.12). In general, fecal concentrations of SCFA, BCFA, ammonia, phenols, and indoles were not altered by supplemental scFOS. Supplementation of scFOS increased fecal concentrations of total aerobes (P < 0.05) and decreased concentrations of Clostridium perfringens (P < 0.05). From these data, it seems that low levels of supplemental fructans have divergent effects on nutrient digestibility and fermentative endproducts, but do not adversely affect nutrient digestibility or fecal characteristics and may improve colonic microbial ecology in dogs. Key Words: Digestion, Dogs, Feces, Fructans, Intestinal Microorganisms, Odors

Growing giant-breed dogs are more susceptible to developing skeletal disorders than small-breed dogs when raised on diets with deficient or excessive Ca content. Differential hormonal regulation of Ca homeostasis in dogs with different growth rates was investigated in Great Danes (GD, n = 9) and Miniature Poodles (MP, n = 8). All animals were raised on the same balanced diet and under identical conditions. Calciotropic and growth-regulating hormones were measured. Production and clearance of 1,25-dihydroxycholecalciferol (1,25[[OH].sub.2][D.sub.3]) were investigated with the aid of [[sup.3]H]-1,25[(OH).sub.2][D.sub.3] and renal messenger RNA abundance of 1[alpha]-hydroxylase and 24-hydroxylase. Intestinal, renal, and skeletal Ca handling were evaluated with the aid of [sup.45]Ca balance studies. Skeletal development was evaluated by radiology and histomorphometry. Great Danes had greater (P < 0.001) growth rates than MP, as indicated by the 17-fold greater body weight gain, by increased longitudinal growth reflected in the increased (P < 0.05) gain in length of the radius and ulna, and by increased (P < 0.001) growth plate thickness. These findings were accompanied in GD by greater (P < 0.05) plasma GH and IGF-I concentrations. Effects were observed for vitamin D3 metabolism, such as greater (P < 0.01) plasma 1,25[(OH).sub.2][D.sub.3] concentrations due to decreased (P < 0.01) clearance rather than increased production of 1,25[(OH).sub.2][D.sub.3], and decreased (P < 0.01) plasma 24,25-dihydroxycholecalciferol (24,25[[OH].sub.2][D.sub.3]) concentrations likely due to competitive inhibition of the production of 24,25[(OH).sub.2][D.sub.3]. These findings were accompanied in both breeds by a limited hormonal regulation of Ca and P absorption at the intestinal level, and in GD by increased (P < 0.05) renal reabsorption of inorganic P ([P.sub.i]) compared with MP, resulting in greater (P < 0.01) [P.sub.i] retention and greater (P < 0.01) plasma [P.sub.i] concentrations. Bone turnover, resorption, and formation were greater (P < 0.01) in GD than in MP. In addition, GD had more irregular (P < 0.01) growth plates than MP, accompanied by disorders of endochondral ossification. It is suggested that in GD, increased calcitonin levels and/or a relative deficiency in 24,25[(OH).sub.2][D.sub.3] at the growth-plate level may both be responsible for the retarded maturation of chondrocytes, resulting in retained cartilage cones and osteochondrosis, and this may be a pathophysiological factor for the increased susceptibility of large breed dogs to developing skeletal disorders. Key Words: Absorption, Bones, Calcium, Cholecalciferol, Dogs, Somatotropin

The effects of calcium (Ca) intake ([V.sub.l]), age and growth rate on intestinal Ca absorption were studied in growing dogs. Two breeds of dogs differing in their growth rate (67 Great Danes and 23 Miniature Poodles) were raised on diets differing only in their Ca content (range 0.33 to 3.3 g/100 g diet on a dry matter basis). Repetitive Ca balance studies were performed with the aid of [sup.45]Ca from 6 wk (i.e., after weaning) until 6 mo of age. Several models were investigated expressing true Ca absorption ([V.sub.a]) as a function of [V.sub.l], breed and age. [V.sub.l] a was directly proportional to a function close to [V.sup.0.82.sub.l] being a continuation of the high Ca needs for mineralization of the growing skeleton. This curvilinear relationship between [V.sub.a] and [V.sub.l] and the inverse relationship between fractional Ca absorption and [V.sub.l] indicated the presence of active and passive Ca absorption in weaned growing dogs. A model in which these two components of Ca absorption can be discerned revealed that active Ca absorption underwent age-dependent changes, whereas passive absorption remained constant and accounted for 53% absorption of the [V.sub.l]. At low [V.sub.l], active absorption contributed to a significant part of the [V.sub.a], whereas at excessive [V.sub.l] active absorption was negligible and passive absorption was the driving force for causing supra positive Ca balance. Intestinal Ca handling did not differ between breeds with dramatically different mature body size and growth rates. KEY WORDS: * True Ca absorption * [sup.45]Ca balance studies * age-dependent changes * Ca intake, dogs

We studied the effects of feeding an antioxidant blend of vitamins, minerals and carotenoids to a mixed adult dog population (n = 40, mean 4.4 [+ or -] 1.85 y) for a 16-wk period. Compared to the control group of dogs (n = 20), the antioxidant (AOX)-supplemented group of dogs (n = 20) demonstrated significant increases in plasma levels of vitamin E and taurine by 4 wk of supplementation (P < 0.01) and total antioxidant activity (as measured by ferric-reducing antioxidant power assay) by 8 wk of supplementation (P < 0.05). Following 8 wk of supplementation, the AOX-supplemented dogs also showed significant reductions in both endogenous and exogenous DNA damage (P < 0.005) compared to that of the control dogs, as measured by the comet assay. Over an 8-wk rabies vaccination course that started at 8 wk supplementation, the AOX-supplemented dogs also demonstrated significantly higher vaccine-specific virus-neutralizing antibody levels at 2, 4 and 6 wk postvaccination (P < 0.05) and a tendency toward establishing a vaccine-specific antibody response quicker than did the control group of dogs. These findings in dogs suggest that antioxidant supplementation can achieve sustained increases in circulating levels of antioxidants that exert a protective effect by a decrease in DNA damage, leading to improved immunological performance. These findings also have implications in a wider context where free-radical damage has been associated with a variety of degenerative disorders and the aging process in general. KEY WORDS: * dogs * antioxidants * DNA damage * comet assay * vaccination

The amount and type of dietary fiber influences the end-products of fermentation and thus fuel availability to intestinal tissue. Metabolic fuel usage was studied in intestinal cells isolated from dogs consuming a commercial diet or from rats consuming either a commercial rat diet or dog diet to examine preferential fuel usage, the effect of diet, and species differences. Production of [sup.14]C[O.sub.2] was measured by incubating cells in media containing either D-[U-[sup.14]C]glucose, [1-[sup.14]C]n-butyrate, L-[U-[sup.14]C]glutamine, or [1-[sup.14]C]propionate with or without competing substrates. The presence of a mixture of 5 mM each of glucose, butyrate, propionate, and acetate and 1 mM glutamine in the media decreased C[O.sub.2] production from glucose, glutamine, and propionate by canine enterocytes (P < 0.05) and from glutamine and propionate by canine colonocytes (P < 0.05). The presence of glutamine in the media decreased glucose oxidation by murine enterocytes, regardless of the diet. Similarly, glutamine decreased glucose oxidation by murine colonocytes (P < 0.05), but only when the rats had consumed the rat diet. Regardless of diet, murine colonocytes oxidized more butyrate (P < 0.01) than did enterocytes, and murine enterocytes tended (P < 0.07) to oxidize more glucose than did colonocytes. The proportion of propionate in colonic contents was higher in dogs than in rats (P < 0.02), and the proportion of butyrate tended to be higher in contents from rats than in those from dogs (P < 0.08). Colonic and cecal wet weights were decreased (P < 0.05) when rats were fed the commercial dog diet. Preferred utilization of substrates by isolated canine enterocytes and colonocytes differed from that of murine intestinal cells. These differences were only partially overcome by feeding the same diet to each species. Key Words: Butyrates, Canis, Glutamine, Intestinal Mucosa

Seven ileally cannulated dogs were randomly assigned to a control or arabinogalactan (AG) treatments in a 7 x 7 Latin square design to evaluate effects of oral AG administration on nutritional and immunological characteristics. Arabinogalactan treatments included a high (1.65 g/d) and low (0.55 g/d) dose of AG100, AG1000 or AG3000 provided via gelatin capsules. Arabinogalactan forms differed in purification procedures. Each period consisted of a 6-d adaptation followed by a 4-d collection. Blood and fresh fecal samples were collected on d 10 of each period. Fecal score increased (P < 0.02) in dogs supplemented with the low dose of AG1000. Ileal and total tract dry matter (DM) and organic matter (OM) digestibilities were not affected by treatment. Dogs supplemented with the high dose of AG1000 tended (P = 0.15) to have a higher concentration of total aerobic fecal bacteria than control dogs. Dogs supplemented with the low dose of AG1000 and the high dose of AG3000 had higher concentrations of fecal lactobacilli (P = 0.04) and tended to have higher concentrations of fecal bifidobacteria (P [less than or equal to] 0.16) compared with control dogs. Dogs fed the low dose of AG3000 tended (P = 0.10) to have a lower concentration of fecal Clostridium perfringens compared with control dogs. Arabinogalactan treatments did not affect (P > 0.05) serum immunoglobulin G, M or A concentrations. Specific forms and doses of AG increased white blood cell, neutropil and eosinophil concentrations. Arabinogalactan is a unique dietary fiber that affects the digestive physiology and immunological characteristics of dogs. KEY WORDS: * arabinogalactan * dogs * immune system * digestion * microflora

Cereal grains represent 30 to 60% of the DM of many companion animal diets. Once incorporated into a diet, the starch component of these grains can provide an excellent source of ME. However, crystallinity and form of starch are variable and can cause incomplete digestion within the gastrointestinal tract. Diets fed in this experiment included one of six high-starch flours as the main source of carbohydrate. The flours originated from barley, corn, potato, rice, sorghum, and wheat. The diets were extruded and kibbled. Starch fraction concentrations of flours consisted of nearly 100% rapidly digestible starch (RDS) and slowly digestible starch (SDS) combined. Starch fraction concentrations of diets paralleled concentrations in flours. Flours varied widely in concentrations of CP, fat, starch, and total dietary fiber. Ileal OM and CP digestibilities were lowest for the potato flour treatment (74 and 64%, respectively). Ileal and total tract starch digestibilities were different (P < .05) among treatments; however, the starch component of all diets was nearly completely digested (> 99%). Total tract digestibility of DM and OM was lowest for sorghum (80 and 84%, respectively) compared to all other diets. Crude protein digestibility was highest for corn (87%). Wet fecal weights tended (P < .08) to be greatest for dogs fed the barley treatment (175 g/d). However, dry fecal weights (dried at 55 [degrees] C) were greatest for dogs consuming the sorghum diet (51 g/d). Fecal scores were consistently greater (i.e., looser stools) for the barley treatment. Any of these flours could be used without negative effects on digestion at either the ileum or in the total tract. Fecal consistency data for dogs consuming the barley treatment indicate that diets containing large amounts (> 50%) of barley may not be advantageous for dog owners who house their animals indoors for most of the day. Key Words: Dogs, Cereal Grains, Starch, Digestion, Ileum

Calcium (Ca) and phosphorus (P) balance is important for skeletal development. Although the effects of deficiencies are well known, reports on the effects of excessive Ca and P supply are relatively scarce. Epidemiologic data and a few controlled studies have shown that skeletal abnormalities may develop when Ca intake is excessive, particularly in periods of rapid growth. Changes in Ca and P balance during and/or after a high Ca intake are thought to underlie this phenomenon. In this study, the effects of excessive Ca (3.1 g/kg dry matter) or Ca and P (Ca 3.1 g/kg, P 2.8 g/kg) intake on Ca and P balance in young, rapidly growing dogs during (for the period from 3 to 17 wk of age) and after (for the period from 17 to 27 wk of age) high Ca and P intake were compared with findings in age-matched controls with normal Ca and P intakes (Ca 1.0 g/kg, P 0.8 g/kg). Dogs fed a high Ca diet developed hypercalcemia, and food intake and fractional absorption of Ca and P were significantly lower at 15 wk of age, whereas endogenous fecal and renal Ca excretion were significantly higher than in controls. This resulted in significantly higher Ca retention than in controls only at 9 wk of age, and in disproportionate absorption of Ca and P. In dogs fed a high Ca and P diet, normocalcemia was maintained, fractional absorption of Ca and P were significantly lower at 9 and 15 wk of age, but retention of both was significantly higher at 9 wk than in controls. The endogenous fecal Ca and renal P losses were significantly higher, but renal Ca excretion was not different from that in controls. After normalization of Ca and P intake, Ca and P balance did not differ among groups. In conclusion, excessive Ca and P intake during early maturation alters Ca and P balance, but does not influence Ca and P balance after dietary normalization. KEY WORDS: calcium; phosphorus; balance studies; diet; dogs

In Exp. 1, soybean hull samples were obtained from nine sources across the United States and analyzed for nutrient content to determine their suitability for inclusion in dog diets. Compositional data revealed variation in both the amount of total dietary fiber (TDF; 63.8 to 81.2%) in the soybean hulls and the ratio of insoluble:soluble fiber (5.0:1 to 15.4:1). Crude protein content varied widely among sources, ranging from 9.2 to 18.7%. An in vivo trial (Exp. 2) was conducted using a premium dog diet containing 3.0, 4.5, 6.0, 7.5, or 9.0% soybean hulls (DM basis). There was a negative linear effect (P < .05) of soybean hull inclusion in the diet on DM, OM, TDF, and GE total-tract digestibilities, as well as on calculated ME. Crude protein and fat digestibilities were unaffected by treatment. based on these results, ileally cannulated dogs were fed diets containing 6.0, 7.5, or 9.0% soybean hulls (DM basis) in addition to diets containing either 0% supplemental fiber or 7.5% beet pulp (Exp. 3). Nutrient digestion at the ileum was unaffected by inclusion of supplemental fiber. Total tract digestion of DM, OM, and GE was lower (P < .05) for diets containing supplemental fiber when compared with the diet containing 0% fiber. Crude protein and fat digestibilities were unaffected by treatment. There was no difference in nutrient digestibility between those diets containing soybean hulls and a diet containing beet pulp. Soybean hull inclusion in the diet resulted in a negative linear effect (P < .05) on calculated ME, in addition to lowering ME (P < .05) when compared with the 0% fiber control diet. Calculated ME for dogs fed a 7.5% beet pulp-containing diet was lower (P < .05) than that for dogs fed the soybean hull-containing diets. Results indicate that soybean hulls can be an effective dietary fiber source in dog diets. Key Words: Dogs, Soybean Husks, Diet, Fiber, Digestibility, Metabolizable Energy

Studies were conducted to determine the dietary amounts of deoxynivalenol (DON; vomitoxin) in dog and cat food that are required to produce overt signs of toxicity (e.g., vomiting or reduced food intake). Wheat naturally contaminated with 37 mg of DON/kg was used to manufacture pet foods containing 0, 1, 2, 4, 6, 8, and 10 mg of DON/kg. Deoxynivalenol concentration in pet food following manufacture was unchanged, indicating that the toxin was stable during conventional extrusion processing. Dogs previously fed DON-contaminated food were able to preferentially select uncontaminated food. Dogs not previously exposed to DON-contaminated food consumed equal quantities of contaminated and uncontaminated food. There was no effect of 6 mg of DON/kg on dog food digestibility. Food intake of dogs was significantly reduced by DON concentrations greater than 4.5 [+ or -] 1.7 mg/kg, and DON greater than 7.7 [+ or -] 1.1 mg/kg reduced cat food intake. Vomiting by dogs and cats was commonly observed at the 8 and 10 mg DON levels. Key Words: Vomitoxin, Toxicity, Dogs, Cats, Feed Intake

The essential nature of dietary fatty acids has been recognized since the 1920s. Nonetheless, a complete description of the essential fatty acid requirements of various animal species, even qualitatively, remains to be established. In addition to linoleic acid [LA, 18:2(n-6)], evidence that (n-3) fatty acids are also essential has been recognized recently in such species as rat, some nonhuman primates, and in humans, especially with respect to nervous system development. The American Institute of Nutrition has recently modified its recommendations for normal laboratory rat diets to contain a fat source such as soybean oil because it contains both 18:2(n-6) and 18:3(n-3) ([Alpha]-linolenic acid, ALA) fatty acids (Reeves et al. 1993). Furthermore, results of animal studies espouse the anti-inflammatory nature of the (n-3) fatty acids and their potential use in the prevention and therapy of chronic diseases (Bauer 1994, Okayuma and Sakai 1991). Most of these studies have been conducted in mice and rats although some reports in horses and dogs have appeared (Bauer 1994, Henry et al. 1990). In some studies, total dietary fatty acid intakes were not completely defined. Thus, specific relationships between dietary fatty acid intake and physiologic responses have not always been clearly established. The carbon chain length of the (n-3) fatty acids fed may also be important, and evidence suggesting their differential metabolism exists in dogs and rodents; other species differences are likely (Bauer et al. 1997, Okayuma and Sakai 1991). Thus, the extent of such differences in fatty acid desaturation and chain elongation, including newly recognized peroxisomal pathways (Voss et al. 1991), may have specific metabolic consequences. Previous studies indicate that several agents affecting peroxisomal proliferation in mice and rats fail to elicit a similar response in dogs, rhesus monkeys or guinea pigs (Lock et al. 1989); humans also appear to be nonresponsive. In view of these observations, the dog was chosen as an experimental model. This species is not only an important companion animal but canine peroxisomal fatty acid metabolism may also be more similar to that of humans and therefore more representative than rodents in this regard. In this study, the time course of enrichment of the plasma lipid subfraction fatty acids in dogs fed a diet specifically enriched in only 18-carbon (n-6) or (n-3) fatty acids (LA and ALA, respectively) was investigated. Chain elongation and desaturation of the 18-carbon precursors of long-chain polyunsaturated fatty acids were evaluated. The data obtained also confirm and extend our earlier observations regarding aspects of differential metabolism of polyunsaturated fatty acids in the canine species (Bauer et al, 1997). Materials and methods. Flaxseed and sunflower seed. Whole flax and sunflower seeds were ground and screened at 200 mesh. They were provided by Essential Nutrient Research (ENRECO, Manitowoc, WI). The seeds were ground to control for digestibility differences that might exist due to seed coats. The whole flaxseed contained 52.7% ALA and the sunflower seed contained 68.2% LA. The other major fatty acids [i.e., 16:0, 18:0 and 18:1(n-9)] were distributed nearly equivalently between these two oilseeds. The use of sunflower seed as a control group allowed treatment comparisons such that dietary fatty acids varied predominately between 18-carbon (n-6) and (n-3) fatty acid series. Animals and diets. A single lot number of a commercially available canine dry, kibbled diet (Hill's[R], Canine Senior) was lightly sprayed with no more than 1% (wt/wt) distilled water in a bakery mixer (Model L800, Hobart Industries, Troy, OH), and the ground seeds were coated on the surface of the kibbled product. The diets were allowed to dry completely and stored indoors in their original bags before being placed in plastic drums fitted with lids until the time of feeding. Portions of these diets were subjected, in triplicate, to total fatty acid extraction, and fatty acid profiles were determined (Table 1). For the study, 18 adult random gender mixed breed dogs, 10-20 kg in body weight, were divided into two groups of 9 each. Three feeding periods were used so that three dogs from each group (6 dogs per day) were fed the supplemented diets, thus ensuring feeding and sample collections in a timely manner. The dogs are property of Texas A&M University, Veterinary Teaching Hospital and were housed in the Small Animal Clinic. Health examinations are routinely performed on this colony throughout the year. Dogs are individually maintained in kennels according to the American Physiological Society Guidelines for Animal Research and according to guidelines set forth by Texas A&M University Care and Use Committee. The basal diet contained ~23.8% energy from fat (about 9.7% fat wt/wt as is), and moderate amounts of protein and fiber. This diet contained 32.5% of total fatty acids (wt/wt) and 7.8% energy as LA. By comparison, the supplemented diets contained ~25% energy as fat. The sunflower seed supplemented diet (SUN) contained 37.5% of the total fatty acids as LA and 1.7% as ALA (Table 1). These values corresponded to 9.3% energy as LA and 0.43% energy as ALA. In contrast, the flaxseed supplemented diet (FLX) contained 27.9% of the total fatty acids as LA and 10.1% ALA. In this case, the FLX diet was determined to have 7.3% energy as LA and 2.5% energy as ALA. At 7-9% energy as LA in both diets, it would be expected that tissue levels would be saturated with LA. Thus the proportion of energy from LA was high and nearly constant (1.3-fold difference), whereas the proportion of energy from ALA was about sixfold higher in the FLX vs. the SUN diet. In this way, a comparison between a low (0.43% energy) ALA diet (SUN) and an enriched (2.5% energy) ALA diet (FLX) could be made. It should be noted that both diets contained about three to four times more LA than the typically accepted minimum of ~2% of energy. A minimum amount of dietary ALA has not yet been established for dogs. All dogs were weighed weekly during the 84-d feeding period. A 2-wk diet acclimation period to the unsupplemented basal diet was used. The dogs were then randomly assigned to either the sunflower or flax group; blood samples were obtained after food was withheld overnight (d 0). Thereafter, the animals were fed their assigned diet and blood samples collected at 4, 7, 14, 28, 56 and 84 d. Sample analyses. Serum was freshly harvested from the blood samples on the day of collection. Total lipids were extracted and subfractionated via TLC and analyzed using gas chromatography. The column oven was temperature programmed starting at 180 [degrees] C, held for 15.5 min, then heated to 210 [degrees] at 12 [degrees] C/min and held for 19 min. Other conditions were as reported previously (Bauer et al. 1997). Statistics. The data were analyzed with two-factor, repeated measures ANOVA followed by Newman-Keuls multiple comparisons to identify treatment differences. Windows version of SAS/STAT Version 6 was used for the analysis (SAS Institute, Cary, NC) and the levels of significance are as indicated. Fatty acid profiles of serum lipid subfractions taken from dogs on d 0, 4 and 84 are presented. Results. Serum lipids. Both total (n-6) and (n-3) fatty acids increased over time in all lipid fractions in the SUN and FLX groups. Further inspection of the data revealed that increases in most individual (n-3) fatty acids occurred over time in the FLX but not the SUN group and diet x time interactions were seen. By contrast, increases in the (n-6) fatty acids were observed over time independently of supplement type and without significant diet x time interactions. It is not surprising that an increase of (n-3) fatty acids occurred in the FLX group because the net fatty acid composition of sunflower plus the basal diet is similar to that of the basal diet alone, whereas the flaxseed plus basal compositi on differs by virtue of its (n-3) fatty acid content (Table 1). A number of additional differences were observed when the SUN and FLX groups were compared. First, (n-3) fatty acid enrichment of FLX group lipid subfractions occurred early on and was distinctive, depending on the lipid subclass examined. More specifically, in the FLX group, phospholipid (PL) fractions were significantly enriched in 18:3(n-3) and 20:5(n-3) at d 4 and thereafter. At the end of the feeding period, significantly higher PL 18:3(n-3) (fourfold), 20:3(n-3) (fivefold), 20:5(n-3) (threefold), and 22:5(n-3) (twofold) were found along with significantly lower 20:4(n-6), 22:4(n-6) and 22: 5(n-6) (Table 2). In the FLX group, it was especially noteworthy that PL-docosahexaenoic acid [DHA;22:6(n-3)] was unchanged during the entire period, indicating some resistance for plasma 22:6(n-3) levels to accumulate in dogs fed 18:3(n-3). Plasma triacylglycerol (TG) fractions of FLX-fed dogs were also enriched in 18:3(n-3) (threefold), 20:5(n-3) (threefold) and 22:5(n-3) (twofold), but again no change in 22:6(n-3) was found (Table 2). Significant increases over time were seen in 18:2(n-6) and 20:4(n-6). In the SUN group, elevations of 22:4(n-6) [the (n-6) analog of 22:5(n.3)] were seen compared with FLX. In the cholesteryl ester (CE) fractions, certain (n-3) fatty acids increased early on in the FLX group, whereas others did not (Table 3). Significant time and time x diet effects were seen for 18:3(n-3) and 20:5(n-3) with diet effects of 18:3(n-3) becoming apparent on d 4 (fivefold difference vs. SUN) and fourfold higher 20:5(n-3) on d 84 vs. the SUN group. By contrast, little 22:5(n-3) or 22:6(n-3) was detected over time in CE, with values never exceeding 0.03 weight %. Discussion. The results clearly show rapid accumulation of eicosapentaenoic acid (EPA) and certain other (n-3) fatty acids in plasma lipids in the canine model when a diet containing a modest increase of ALA is fed. Similar results have been observed in human studies with a 4-wk feeding period (Mantzioris et al. 1994). The observed changes appeared to achieve a steady state after ~28 d, although EPA continued to increase modestly throughout the 84-d feeding period. It is especially noteworthy in the FLX group that PL-DHA [22:6(n-3)] was unchanged during the entire period. This finding indicates some resistance for plasma DHA levels to accumulate in dogs fed ALA at the diet level employed in this study. It is known that conversion of 22-carbon precursors to DHA occurs in canine neurologic tissues and is believed to occur in peroxisomes (Alvarez et al. 1994). However, canine hepatic peroxisomes, unlike those of rodents, may not readily proliferate under various conditions, and conversion in canine liver may be subsequently slowed (Lock et al. 1989). A similar finding has recently been reported in cats (Pawlosky et al. 1994). Taken together, these data raise the intriguing possibility that there is limited conversion of ALA to DHA in liver of certain species even when docosapentaenoic acid [DPA; 22:5(n-3)] is produced. This latter fatty acid might then be transported via plasma lipids to important neurologic tissues for subsequent DHA synthesis (Pawlosky et al. 1994). In an earlier study with dogs, we observed that when fish oils are fed, 22:5(n-3) does not appear in the CE fraction, but that 22:6(n-3) does (Bauer et al. 1997). In this study, using dietary flaxseed, 22:5(n-3) was seen both in plasma PL and TG, but little 22:6(n-3) was found. Again, in spite of this enrichment in the PL fraction, no plasma CE 22:5(n-3) was detected. Taken together, these data suggest the possibility that forward transport of hepatic 22:5(n-3) via plasma PL and TG to tissues is likely, but reverse cholesterol transport of this fatty acid to the liver as CE mediated by the lecithin cholesterol acyltransferase reaction does not occur. The significance of these observations and their similarity to humans remain to be determined. However, we hypothesize that, in dogs, peroxisomal conversion of 22:5(n-3) to 22:6(n-3) is slow and that after hepatic synthesis of 22:5(n-3) from 18:3(n-3), this fatty acid is subsequently transported to important neurologic tissues via plasma PL and TG, especially when dietary sources of 22:6(n-3) are scarce. Because 22:5(n-3) is absent in CE, such transport may be unidirectional. In this way, substrate for DHA synthesis in neurologic tissues may be conserved. Future studies are in progress to investigate these possibilities. KEY WORDS: * dogs * phospholipids * cholesteryl esters * (n-3) fatty acids * flaxseed

Great variations in the postprandial glucose concentration and insulin secretory responses to different foods have been shown in dogs (Holste and al. 1989, Nguyen and al. 1994). It has been suggested that foods yielding low glycemic responses would be recommended for diabetic or obese subjects and in the prevention of many other disorders. High carbohydrate/high fiber diets enhance peripheral glucose disposal and decrease insulin requirements in insulin-dependent diabetic subjects. In overweight patients with noninsulin-dependent diabetes mellitus (NIDDM), reducing diet glycemic response improves overall blood glucose control, long-term glycemic control and lipid control. Diets with a high glycemic response that are low in fiber increase the risk of NIDDM in humans. Foods with a low glycemic response combined with a high dietary fiber content decrease free fatty acid level, which is associated with abdominal obesity and cardiovascular risk. They cause rapid intestinal absorption of glucose into the blood, leading to postprandial hyperinsulinemia, which may play a role in promoting colon carcinogenesis. A diet high in refined carbohydrates and low in water-soluble fiber causes rapid absorption of glucose with similar results. Because of the clinical implications of the glycemic index, notably in diabetes management or in dietary strategy to avoid or treat overweight or moderate obesity, the factors that affect it have been the subject of many studies (Wolever and al. 1991). The extent of postprandial hyperglycemia and insulin secretion depends on the amount of food and carbohydrate consumed per meal. However, different kinds of carbohydrate elicit different glucose and insulin concentrations, because their chemical nature, especially the ratio of amylose to amylopectin forms of starch, may affect their rate and speed of digestion. Dietary fiber slows down the rate of passage and the rate of hydrolysis of starchy polysaccharides (Wolever 1990). Dietary fat delays stomach emptying (Gulliford and al. 1989), and high intakes of rapidly digested proteins modify the glycemic response by increasing insulin secretion (Nuttall and Gannon 1990). The food processing may be of particular importance for dog food. The type of food, dry, canned or soft moist, affects the maximal postprandial glucose concentration as much as the time at which this peak occurs (Holste and al. 1989). The glycemic index methodology is based on tests of single foods and could be applied to the testing of mixed meals. Nevertheless, its practical utility is controversial because differences among foods could be partially abolished in mixed meals by the effects of protein and fat. Whatever it may be, an individual food evaluation is not realistic in dogs. Their complete foods contain many components. There are large variations in their protein and fat content and the technological processes can largely modify the intrinsic carbohydrate availability. Nevertheless, information concerning postprandial responses would be of great interest in regard to obesity. Along with a long-term excessive energy intake, food quality may play a significant role according to its humoral and metabolic effects. This information may also be of interest in the management of NIDDM (which elicits alteration of carbohydrate tolerance and insulin action) as much as insulin-dependent diabetes mellitus (IDDM; reduction of fluctuations in blood glucose, synchronization of glucose increase and insulin administration). The purpose of this study was to determine how the differences in carbohydrate (starch and dietary fiber, soluble and insoluble), protein and fat content of complete (and complex) foods given to healthy dogs in a single meal on a normoenergetic basis modify their postprandial plasma glucose and insulin responses. Material and methods. Animals. Twelve adult (older than 15 mo) beagle dogs were studied, according to the French Ministry of Agriculture and Fisheries regulatory rules for animal welfare. They were allotted to two groups; from each group, five dogs were used alternately for tests, excluding in particular dogs that did not eat the entire meal that they were offered. None of the dogs was obese (13.5 kg mean body weight) and they were clinically normal. Their basal plasma glucose (5.21 [+ or -] 0.50 mmol/L) and their response to the intravenous glucose tolerance test (performed after a 24-h period of food deprivation, using a glucose dose of 500 mg/kg body weight, infused as 50% glucose solution in 30 s) were also normal. These dogs were accustomed to the experimental procedure. They were commonly used for digestibility trials in the cages used in this study and had been previously subjected to repeated venipuncture. Therefore, their responses were due to the experimental variables and not to stress. Experimental diets. Twenty experimental foods (C1-C5 and D1-D15) were tested. Foods D1-D15 were dry foods, whereas C1-C5 were canned. These test foods were intended to be representative of foods currently used for maintenance or for clinical purposes in adult dogs. They were designed to vary in macronutrient composition [15.4-62.6% crude protein (CP), 7.9-31.0% ether extract (EE), 3.2-39.1% total dietary fiber (TDF) and 0.4-52.7% starch (ST), on a dry matter basis]; the energy content was 965-2045 kJ/100 g dry matter. The composition of test meals is shown in Table 1. The daily chromium intake was not KEY WORDS: * dog foods * analytical composition * food processing * glycemic response * insulinemic response * dogs

Variations in the blood glucose and insulin responses to different foods have been studied in dogs (Holste et al. 1989, Nguyen et al. 1994), and different trends in postprandial concentrations have been observed. These differences arose in the extent of the variations (areas under the curves and maximal increments) and the time from meal to peak increases. The main purpose of these studies was to rank foods on the basis of the incremental glucose responses that they produced and to relate these responses to foods characteristics. It is known that methodologic variables can markedly modify the interpretation of the glycemic response. In particular, this concerns the length of time of blood sampling (Gannon and Nuttall 1987), short-term (Wolever and al. 1988) and long-term (Cannon and al. 1980) remnant effects of the previous meal, blood sampling (Jackson and al. 1983) and fasting blood glucose values (Nielsen and Nielsen 1989). In dogs, the variations of the glycemic response have been evaluated with (Holste et al. 1989) or without (Nguyen et al. 1994) an adaptation period to the tested meals. As in human beings, the plasma concentrations were measured over a period of 3 or 4 h even though the gastrointestinal transit time is shorter in dogs than in humans. The purpose of our study was to examine whether an adaptation time (inducing digestive changes and modifications in basal insulin secretion and glucose tolerance) modifies the postprandial response to meal feeding in normal dogs. We also studied the effect of length of time of blood sampling on the consistency of the response value expressed by the areas under the glycemic and insulin curves, the peak incremental values and the times from meal to peaks. Materials and methods. Animals. Twelve adult (older than 15 mo) beagle dogs, allotted to two groups, were studied, according to the French Ministry of Agriculture and Fisheries regulatory rules for animal welfare. None of the dogs was obese (13.7 kg mean body weight) and all were clinically normal. Their basal plasma glucose (Experiment 1:5.41 [+ or -] 0.54 mmol/L; Experiment 2:5.27 [+ or -] 0.55 mmol/L) and their response to the intravenous glucose tolerance test (performed after a 24-h period of food deprivation), using a glucose dose of 500 mg/kg body weight, infused as 50% glucose solution in 30 s, were also normal. These dogs were accustomed to the experimental procedure. They were commonly used for digestibility trials in the cages used in this study and had been previously subjected to repeated venipuncture. Therefore, their responses were due to the experimental variables and not to stress. Experimental diets. Two experiments were performed according to the two objectives. Experiment 1. Five experimental foods (A1, A2 and B1-B3 foods) were tested. Foods A1 and A2 were canned foods, whereas B1-B3 were dry. Foods B1 and B3 were given as is, with separate water, whereas food B2 was hydrated before feeding. These test foods were intended to be representative of foods currently used for maintenance in adult dogs. They were designed to vary in macronutrient composition [27.2-62.6% crude protein (CP), 10.9-25.7% ether extract (EE), 1.1-3.6% crude fiber (CF), 4.4-50.5% nitrogen-free extract (NFE) and 3.2-12.4% total dietary fiber (TDF), on a dry matter basis]. The energy profile was as follows: 25-54% energy derived from protein, 25-51% from fat and 4-48% from nitrogen-free extract, according to standard energy conversion factors, 14.6 kJ/g CP or NFE, 35.6 kJ/g EE). The composition of the test meals is shown in Table 1. The daily chromium intake was not 90 min appears to be unnecessary to characterize the glycemic and insulin responses to meals in normal dogs. The effects of the length of time of blood sampling on the relative area under the glucose curve of foods in humans has been reviewed (Gannon and Nuttall 1987). Long-time measurements tend to reduce the differences in AUCG between foods, especially between foods resulting in high peak rises followed by a rapid decrease, and foods for which the glucose response presents a lower peak but tends to remain above the baseline for a prolonged period of time. If measured for too long a time, the area under these types of curves may be nearly the same, despite markedly different effects on insulin and counterregulatory hormone responses. These factors are related to the acute rate of carbohydrate absorption, which in turn is related to the incremental area under the early part (120 min) of the glucose response curve in normal subjects (Wolever et al. 1991). A shorter duration of blood sampling could be sufficient in normal dogs because of their high gastrointestinal transit rate. The relatively rapid gastric emptying and digestive processes allow an early expression of the acute effects of foods on the glucose response curve. Increasing the period of blood sampling beyond 90 min did not modify the discrimination between foods. We concluded that the diet consumed before the initiation of the study had not influenced the response to test foods and that an adaptation time appears to be unnecessary. The postprandial glycemic and insulin responses of normal dogs may be obtained after a single meal. We also conclude that a 90-min blood sampling period was sufficient to characterize the glycemic and insulin responses in normal dogs. KEY WORDS: * dog foods * glycemic response * insulinemic response * dogs