' Can I feed my dog vegan dog food?' Given the life-giving health benefits plant-based ingredients provide, perhaps the question should be 'Why shouldn't I feed my dog vegetarian dog food?'

Some of the health benefits of phytonutrients in plant-based foods include enhanced immune system activity, protection against cancer, support of eye and heart health, improved communication between cells and repair of DNA damage.

Antioxidants also help slow down the signs of aging by cleaning up the by-products of oxidation within the body’s cells.

Roles of plant-based ingredients and phytonutrients in canine nutrition and health

Body weight and body condition:

  • A supplement containing carotenoids (β-carotene, lutein and zeaxanthin) given to puppies tended to reduce fat mass and improved fat oxidation and lipid profiles (Wang et al., 2017).

Insulin sensitivity and glycaemic control:

  • Use of annatto (high carotenoid content) suppressed the postprandial rise in blood glucose level and increased plasma insulin level after an oral glucose load (Russell et al., 2005).

Cardiovascular outcomes:

  • β-Carotene, lutein and α-tocopherol given together increased plasma antioxidant concentrations and decreased oxidative damage post-exercise (Baskin et al., 2000).

Immune health:

  • In Beagle dogs fed varying levels β-carotene, plasma antibody immunoglobulin G concentrations were found to increase dose-dependently (Chew, Park, Weng, et al., 2000; Chew, Park, Wong, et al., 2000).
  • Dogs provided β-carotene showed higher CD4+ T-cell levels and displayed increased delayed-type hypersensitivity (DTH) response to both specific and non-specific immune response triggers (Chew, Park, Weng, et al., 2000; Chew, Park, Wong, et al., 2000).
  • In older dogs supplemented with β-carotene, immunological variables were altered by increasing levels of CD4+ T cells, improving T-cell proliferation, and heightening DTH responses (Massimino et al., 2003).
  • Yellow-orange vegetables and green leafy vegetables were significantly associated with a decrease in risk of developing transitional cell carcinoma of the urinary bladder in Scottish Terriers (Raghavan et al., 2005).
  • Lutein provided to female Beagle dogs displayed immune-modulating effects, by enhancing DTH to immune response triggers, increasing immunoglobulin G production and increasing the population of several lymphocyte subsets (Kim et al., 2000).
  • A diet consisting of spinach flakes, tomato pomace, grape pomace, carrots, citrus pulp and other antioxidative nutrients in combination with behavioural enrichment, served to increase neutrophil phagocytosis and B-cell populations in aged Beagles (Hall et al., 2006).

Bone and joint health:

  • Treatment of canine osteosarcoma cells with lycopene reduced cell proliferation and induced apoptosis of different cell lines to varying degrees (Wakshlag & Balkman, 2010).

Renal health:

  • Supplementation with vitamin E and carotenoids reduced proteinuria, glomerulosclerosis and interstitial fibrosis in Beagle dogs (Brown, 2008).
  • A diet consisting of beet pulp, citrus pulp, carrot granules, dried spinach, tomato pomace along with other antioxidative nutrients significantly decreased levels of SDMA and creatinine, and improved canine renal function (Hall, MacLeay, et al., 2016; Hall, Yerramilli, et al., 2016).
  • A traditional renal protective food diet was provided to aged dogs and supplemented with functional foods, including beet pulp, citrus pulp, carrot granules, dried spinach, tomato pomace and other antioxidative nutrients; serum SDMA decreased in those supplemented with functional foods (Hall, MacLeay, et al., 2016; Hall, Yerramilli, et al., 2016).

Visual Health:

  • A daily dose of lutein, zeaxanthin, β-carotene, astaxanthin, vitamin C and vitamin E significantly improved retinal responses in Beagle dogs with healthy eyes (Wang et al., 2016).

Cognitive Health:

  • A diet containing spinach flakes, tomato pomace, grape pomace, carrot granules, citrus pulp and other antioxidative ingredients was used in several cognitive trials. It showed that dogs receiving the fortified diet learned the landmark discrimination learning task more rapidly (Milgram, Head, et al., 2002; Milgram, Zicker, et al., 2002), and performed better on the oddity discrimination learning task at higher levels (Milgram, Head, et al., 2002; Milgram, Zicker, et al., 2002). Additionally, those receiving the fortified diet in combination with a behavioural intervention performed better on size discrimination reversal-learning task (Milgram et al., 2004), and on several learning tasks in a two-year follow-up (Milgram et al., 2005).

Body weight and body condition:

  • Dogs fed diets with 25% higher than required calories, supplemented with soy isoflavones, gained significantly less weight than dogs not receiving soy isoflavones (Pan, 2006).
  • Overweight dogs consuming soy isoflavones were more likely to achieve weight loss goals than dogs on diets without soy isoflavones (Pan et al., 2008).
  • Green tea polyphenols were shown to attenuate the impacts of a high-fat diet on weight gain and inflammation in healthy male Beagles (Rahman et al., 2020).
  • Consumption of green tea polyphenols was found to have a positive impact on weight status, inflammation and gut microbiota populations in dogs (Li et al., 2020).

Insulin sensitivity and glycaemic control

  • The polyphenol content of rosemary and basil reduced fasting glucose levels in Rottweiler dogs (Abdelrahman et al., 2020).
  • Green tea polyphenols improved the insulin sensitivity index by 60% in obese dogs (Serisier et al., 2008).

Gastrointestinal health and the gut microbiota

  • Grape proanthocyanidins were demonstrated to alter the abundances of select faecal microbiota populations and SCFAs in healthy adult dogs (Scarsella et al., 2020).
  • Polyphenol supplementation from pomegranate peel extract increased faecal concentrations of total SCFAs and fermentative metabolites, and improved antioxidant status in healthy dogs (Jose et al., 2017).
  • Supplementation with green tea polyphenols altered the structure of the gut microbiota in adult male dogs (Li et al., 2020).

Cardiovascular outcomes:

  • Blueberries were shown to attenuate post-exercise oxidative damage and elevate antioxidant status in healthy sled dogs (Dunlap et al., 2006).
  • Quercetin, a flavonol, given at 50 mg/kg was found to be cardioprotective in dogs given an experimental myocardial infarction (Kolchin et al., 1991).
  • Purple grape juice, high in flavonoids quercetin, kaempferol and myricetin, given to dogs with coronary stenosis, was shown to have antithrombotic effects (Demrow et al., 1995; Osman et al., 1998).
  • Grape seed and skin extracts given together inhibited platelet aggregation in healthy dogs (Shanmuganayagam et al., 2002).
  • Resveratrol, and other antioxidants, from a formulation containing blueberry, strawberry, blackberry and grape seed extracts significantly reduced exercise-induced oxidative stress (Sechi et al., 2017).

Bone and joint health:

  • Curcumin provided to dogs with osteoarthritis (OA) was found to provide supplemental anti-inflammatory actions (Colitti et al., 2012).
  • Supplementation of turmeric extract (6.6 mg/kg body weight of curcumin) led to a downregulation of inflammatory genes in circulating white blood cells in dogs with a history of OA (Sgorlon et al., 2016).
  • Use of P54FP, an extract of turmeric containing curcuminoids, was used in the treatment of dogs with OA, and study investigators, but not owners, noted improvement (Innes et al., 2003).
  • Treatment of canine osteosarcoma cells with the flavonoid baicalein reduced cell proliferation and induced apoptosis of different cell lines to varying degrees (Helmerick et al., 2014).
  • Avocado/soya bean unsaponifiables (ASU) provided to dogs with experimental OA were found to improve structural changes associated with the early stages of OA (Boileau et al., 2009).
  • ASU supplementation increased cytokine TGF-β1 and TGF-β2 levels in the synovial fluid of healthy dogs, which are linked to cartilage synthesis (Altinel et al., 2007).
  • The flavonoid myricetin was shown to induce apoptosis in canine osteosarcoma cells (Park et al., 2018).

Skin and coat health:

  • An in vitro study using a nutrient combination that included curcumin demonstrated promise in helping to maintain the canine skin barrier (Fray et al., 2004).
  • Healthy dogs fed high- or low-isoflavone soy-based diets, had no detectable differences in skin and coat health, indicating soy as a safe ingredient for dogs with skin and hair issues (previously thought to have negative impact) (Cerundolo et al., 2009).
  • Both healthy dogs supplemented with flax or sunflower seeds showed improvements in their skin and coat condition scores after 1 month (Rees et al., 2001).
  • Black currant seed oil given to dogs with atopic dermatitis showed nonsignificant clinical improvements (Noli et al., 2007).
  • An in vitro study showed that a nutraceutical mixture containing phenolic compounds downregulated the expression of inflammatory genes in inflamed canine keratinocytes and monocytes (Massimini et al., 2021).

Cognitive Health:

  • Healthy aged Beagles receiving mixed grape and blueberry extract showed improvements in their working memory (Fragua et al., 2017).

Cardiovascular outcomes and insulin sensitivity:

  • Phytosterols in beans are suspected to be responsible for the cholesterol-lowering effects, with overweight dogs receiving dry black or navy bean powder decreasing serum total cholesterol. Navy bean consumption also led to a decrease of serum triglyceride levels (Forster et al., 2012).
  • Navy beans lowered serum cholesterol in healthy adult dogs (Forster et al., 2015).
  • Dogs gaining weight on a corn oil diet had a small increase in mean arterial pressure and no change in insulin sensitivity, while those on a lard diet experienced a large increase in mean arterial pressure and some insulin resistance (Truett et al., 1998).

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