ISSUE FOCUS FEED & ADDITIVE MAGAZINE September 2024 27 MANAGING OXIDATIVE STRESS WITH ENZYMES, ANTIOXIDANTS, AND DAMAGE REPAIR Understanding the two key strategies for combatting free radicals and reducing oxidative stress can empower producers’ efforts to manage animal health. The first line of defence involves enzymes that convert free radicals into harmless substances like water and oxygen. Enzymes such as catalase, superoxide dismutase, and glutathione peroxidase, containing selenium, play a crucial role in this strategy. The second line of defence is formed by antioxidants, including vitamins E and C, lipoic acid, and glutathione, which neutralize free radicals, preventing them from causing further damage. Antioxidants reduce free radicals by donating a hydrogen atom. Vitamin E, for example, contains a benzene ring with a hydroxyl group attached. The electrons in the benzene ring are mobile, allowing the hydrogen in the hydroxyl group to separate and neutralise a free radical. Vitamin E also has a long lipophilic tail, allowing it to function as a lipid in digestion and the body (Figure 1). COMBATTING FREE-RADICAL DAMAGE – ALTERNATIVES TO VITAMIN E Vitamin E's function as a gene regulator is more critical than its antioxidant properties. Nothing can replace vitamin E in this capacity. However, other antioxidants can replace vitamin E to prevent and combat free-radical damage if they function in the same cellular region and have a similar affinity for free radicals (Figure 2). In fact, other antioxidants may be even more effective than vitamin E in the fight against free radicals. A vitamin’s bioavailability should always be considered given that the animal must be able to access and utilize the vitamin to obtain its beneficial properties. The synthetic vitamin E used in animal nutrition is a blend of eight stereoisomers, one of which only one has the same spatial structure as naturally occurring vitamin E which offers good bioavailability. The liver does not adequately recognise the remaining seven stereoisomers, which are primarily returned to the digestive tract and excreted unused. CONSIDERING BIOAVAILABILITY AND SPECIES The bioavailability of vitamin E in cattle is highly variable and depends on the balance between intake, absorption, retention, and degradation of vitamin E. The bioavailability of vitamin E in pigs and poultry is affected by several factors, such as the age and physiological status of the animals, the dietary fat content and composition, and the presence of other antioxidants and pro-oxidants. Furthermore, vitamin E’s half-life shortens with increasing doses, making it hard to achieve plasma levels greater than three times the baseline. To ensure a high level of antioxidant defence in animals, particularly those who are fast-growing or have health issues, it is critical to combine a variety of antioxidants that function synergistically and complement one another. HO Figure 1. Molecular structure of vitamin E Gene expression Vitamin E Polyphenols Enzymatic activity regulation Neurological functions Anti-oxidant Prevent lipid oxidation Functions in reproductive, muscular and immune systems Figure 2. Selected polyphenols can act as a partial Vitamin E substitute.
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