There is a growing body of evidence demonstrating that antioxidants benefit both man and animals. They manage the damaging impact of free radicals on the body. Appropriate antioxidant nutrition therefore has a role to play in the development of functional pet food products designed for specific life-stages, lifestyles or activity level, and support functionality of food products designed to address specific health or wellbeing concerns.
Free radicals are unstable molecules with one or more unpaired electrons. They are produced during normal body reactions such as the immune response and during aerobic cellular respiration due to the incomplete consumption of oxygen. External environmental factors also impact the production of free radicals in the body (Figure 1).
Free radicals damage cellular lipids, cellular proteins, DNA and critical cellular structures. Free radical damage is linked to inflammation in the body and to the development of some diseases and aging.
Antioxidants help maintain oxidative balance in the body. They readily donate their own electrons to radicals, which breaks the chain reaction of free radical proliferation. The down side to any antioxidant is that once it has donated an electron, it too becomes a radical requiring another antioxidant to recycle it back to a beneficial form. Effective antioxidant support is therefore about providing a range of complementary dietary antioxidant nutrients to support their regeneration. (Figure 2).
Fat soluble vitamin E has several functions in the body. It is vital for stabilization of the cellular lipid membranes, regulation of gene expression in addition to its antioxidant properties which prevent oxidation of fatty acids. Dietary vitamin E supplementation of both dogs (445 iu/kg diet) and cats (540 iu/kg diet) was shown to support overall antioxidant status as demonstrated by reduced plasma alkenes. Total alkene is an indicator of lipid peroxidation, which may be a result of in vivo oxidative reactions.
Carotenoids scavenge radicals and act as chain breaking antioxidants. They also act through the formation of radical adducts that in themselves are highly stable and act to terminate radical reactions. One of the most widely known carotenoids of benefit to humans and animals is beta-carotene. Carotene was first revealed to have protective effects against infectious disease in humans during the early 1930s. Besides carrots, beta-carotene is also found in other plants, for example, in bright colored fruits and the leaves of green vegetables, such as spinach, cabbage and broccoli. Beta-carotene is a powerful antioxidant in mammalian systems.
Vitamin C is a water-soluble antioxidant and is the primary hydrophilic antioxidant in the plasma. It also has an important role to play in the regeneration of oxidized vitamin E. Dogs and cats have a limited capacity to synthesize vitamin C, compared with other species. A challenge to the system could potentially render the supply of vitamin C from this synthesis becoming insufficient. The key to antioxidant nutrition is about maintaining a suitable antioxidant and pro-oxidant balance. It is suggested that some dietary supplemental vitamin C could therefore be beneficial in some circumstances.
Eye sight is often impaired as animals age. A link between lenticular oxidation processes, cataract formation and antioxidant intake and retardation in age-related cataractogenesis is suggested. A lifetime approach to antioxidant nutrition may therefore be supportive of the eye.
Macrophages and neutrophils generate free radicals, in an oxidative burst, when stimulated as part of the normal immune response to kill bacterial pathogens. Ascorbic acid levels are high in phagocytic cells. Ascorbic acid can help protect these cells from oxidative damage, along with vitamin E. Neutrophils from vitamin E deficient animals have been shown to have increased amounts of peroxidized lipids in their membranes.
Vitamin E supplementation in the cat has been shown to alter and enhance the immune system. It was found that a level of 225 mg/kg of vitamin E appeared to have beneficial effects on immune function. In dogs, one study reported that a cocktail of antioxidants vitamin C, vitamin E, taurine, lutein, lycopene and beta-carotene had improved total antioxidant activity, significant reductions in both endogenous and exogenous DNA damage and improved immunological performance. Another study reported optimal immune response in cats fed 10 mg beta-carotene per day, noting improved cell mediated and humoral immune response.
Breeding and Young Animals
In order to allow the immune system to optimally respond to stress during the early weeks of a young animals’ life, appropriate nutrition for the mother during gestation to support colostrum quality, as well as the puppy or kitten during the early neonatal period is essential. In puppies, dietary supplementation an antioxidant cocktail (vitamin E at 500 IU/kg dry matter (DM), vitamin C at 70 mg/kg DM, beta-carotene (0.4 mg/kg DM) and selenium (0.8 mg/kg DM)) supported a better vaccination immune response. Similarly, antioxidant supplementation of kitten diets with taurine, vitamin E, vitamin C, lutein, beta-carotene and lycopene supported a stronger humoral immune response. Antioxidants have therefore an important role to play in the support and development of a strong immune system in the young.
Adult Pets and Seniors
Adult pets need optimal nutrition to support immune function, and to deal with the daily challenges of life as they age or engage in active or working lifestyles. The ageing process has been described as ‘inflammageing’ and defines the effects of a lifetime of constant antigenic challenge and associated production of inflammatory mediators that may trigger the onset of inflammatory disease in later life. Dietary factors including a polyphenol-rich diet from fruits, vegetables, and herbs, as well as diet rich in omega-3 fatty acids and some vitamins such as vitamin E and C, appear to have beneficial effects in reducing systemic inflammation in ageing.
In senior dogs and cats, immuno-senescence is also observed, in that immune capacity of older animals is lower than that of younger animals. One study found that beta-carotene supplementation significantly restored immune responses in older dogs when compared with their age-matched controls and younger counterparts. Another study found that extra vitamin E supplementation helped support the immune system of the older cat to a level similar to that seen in younger cats.
Ageing and cognitive decline
Cognitive decline in pets is a growing concern due to longer lifespan. Ageing typically involves an increase in the presence of oxidative damage and changes to, or a reduced antioxidant capacity. Oxidative damage to the brain is particularly of concern due to its high metabolic rate, high lipid content and poor regenerative capacity. Many believe this damage in the brain is related to cognitive decline. Some studies indicate intervention with antioxidants alone, or in conjunction with behavioral enrichment helps to offset some cognitive decline.
Performance and Exercise
Up-regulation of endogenous antioxidant enzymes are observed in studies involving exercised dogs. This does not mean however that these animals need any less dietary support, as upregulation of nutrient dependent systems requires the diet to contain adequate antioxidant nutrients. Where dogs are shown to upregulate their antioxidant systems when challenged by increased metabolic demands such as exercise or disease there is evidence to suggest this is not always enough to completely combat the challenge, thus dietary supplemental antioxidants would appear to be necessary. The results from a study examining the effects of the dietary supplemental antioxidants vitamin A, E, C and green tea polyphenols in dogs undertaking exercise indicated better tolerance to exercise.
According to the Pet Food Manufacturers Association, UK (2017), 52% of dogs and 47% of cats are overweight. This indicates a need for specific and effective weight maintenance diets. Pet owners are however often unwilling to accept that their pets are overweight, so need to see a reason to buy weight management products. Obese dogs have been observed as having higher ratio of omega-6 to omega-3 fatty acids, a lower proportion of omega-3 and lower omega-3 index compared to lean dogs. Obese dogs are therefore characterized by a more ‘proinflammatory’ serum fatty acid profile and with increased oxidative stress. This may suggest that a diet rich in antioxidants and a change in dietary omega 3 supply may be appropriate.
Some data is available to suggest that antioxidant supplementation may be of benefit to support overall wellbeing in relation to certain conditions of the heart, the skin, the joints and renal system. It should though be remembered that when making claims around nutrients, no inference to treat, prevent or cure should be made.
When developing functional diets, it is important not only to utilize the correct ingredient or nutrient to ensure the diets’ functionality, the pet parent must also believe in the nutrition that is supplied. DSM’s 2015 U.S. pet consumer study shows pet parents are making the connection between healthy ingredients for humans and the potential benefit for their pets (Table 1). Comparing the agreement score for the statement about antioxidants to the statements about prospective healthful ingredients is a good first step in understanding their appeal to pet consumers.
Compelling scientific and consumer data exist to support the addition of beneficial dietary antioxidants in companion animal food products. This gives food producers good opportunity to differentiate and develop functional food products that are appealing to pet parents as the seek to provide the very best nutrition to their companions.
Reference list is available upon request
25 April 2019
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