Free Radicals vs. Antioxidants

When Free Radicals Induce Oxidative Stress, Antioxidants Come To The Rescue

Free Radicals vs. Antioxidants

Free radicals happen. They happen to us humans, and they happen to our chickens. They are unstable molecules that damage body cells, impair immunity and contribute to the development of disease. They also hasten aging.

Oxidative stress occurs when free radicals outnumber the body’s supply of antioxidants — natural compounds that repair the damage caused by free radicals, and that also destroy the radicals. For our chickens to enjoy long and healthy lives, we need to control oxidative stress by ensuring our birds get sufficient antioxidants to keep free radicals in check.

How Free Radicals Happen

We all, chickens and humans alike, take oxygen into our bodies by breathing. Oxygen regulates metabolism, the process encompassing all physical and chemical reactions that maintain the body, including blood flow, heartbeat and energy production.

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Due either to natural cellular activity or to environmental toxins, the occasional oxygen molecule loses an electron. Since electrons normally come in pairs, one positive and one negative, the damaged molecule becomes an electrically charged, unstable fragment. In trying to restabilize itself, the molecule bounces around in the body, seeking to steal an electron from some other hapless molecule. This high-energy, destructive molecule is known as a free radical because it possesses a free (unpaired) electron, making it radically different from a normal oxygen molecule.

When a free radical becomes stabilized by stealing an electron from another molecule, it destabilizes that molecule. In turn, the newly destabilized molecule seeks to steal an electron from some other molecule, thereby setting off a chain of free radical reactions.

All this electron stealing causes damage to the body’s cells. A large number of chain reactions can cause cells to lose their ability to perform whatever their specific function is in the body, and can even lead to cell death. Since free radicals result from the body’s oxidative processes, damage caused by their chain reactions is called oxidative stress.

Oxidative stress itself can cause disease. But more often it weakens a chicken’s immune system, making the bird more vulnerable to diseases that have other causes. Nearly every common disease is associated with oxidative stress. In a bird that’s already ill, oxidative stress can make things worse. If the bird is injured, healing can take longer.

Ironically, while an accumulation of too many free radicals is harmful, the presence of some free radicals can be beneficial. Free radicals naturally result from the oxidation of carbohydrates, fats and proteins to provide energy for the chicken’s body to function. And a chicken’s immune system may create them on purpose to neutralize harmful bacteria and tumor-causing viruses.

Furthermore, the body of an active chicken, such as one that spends most of the day foraging, produces more free radicals than the body of a less active chicken, because active muscles need more oxygen. And the more oxygen the muscles use, the more free radicals they produce.

To maintain balance, the body therefore needs a way to control excess numbers of free radicals. In chickens and humans alike, free radicals are controlled by molecules known as antioxidants.

Antioxidants to the Rescue

The body of a young chicken (or a young person) keeps free radicals in check by creating its own antioxidants to supplement those acquired through diet. As a body ages, however, antioxidant production decreases. Production can also be impaired by pollutants, poor diet, and some medications — a good reason, right there, to provide your chickens with a clean environment and healthful diet, and to avoid the unnecessary use of drugs.

As the body’s antioxidant production decreases, the need for dietary antioxidants increases. Dietary antioxidants come from plants. Antioxidants are vitamins, minerals and other organic chemicals that neutralize free radicals, reducing or preventing the damage they cause, and also helping repair cells damaged by them.

Plants produce antioxidants to protect themselves from pathogens, pollution and harmful ultraviolet sunlight. The best-known antioxidants are vitamins A, C, and E and the mineral selenium. However, regularly feeding your chickens such antioxidants in the form of concentrated dietary supplements can lead to toxicity. On the other hand, treating your chickens to plants that are naturally rich in antioxidants can help them live long and healthy lives.

Vitamin A is called the anti-infection vitamin because, as an antioxidant, it aids disease resistance. Vitamin A deficiency can occur in chickens that have no access to green forage and are fed stale commercial rations or improperly balanced home-mixed rations. It may also be caused by a health condition, such as coccidiosis or worms, that interferes with nutrient absorption. Green forage is an excellent source of vitamin A, as are richly colored fruits and vegetables like sweet potatoes, cantaloupe, carrots, kale, spinach and broccoli.

Vitamin C helps prevent diseases both as an antioxidant and by reducing the harmful effects of stress. Chickens make their own vitamin C and normally do not need a supplement, except when the absorption of nutrients is inhibited by stress, such as might occur because of hot weather, overcrowding or disease. Among the best sources of vitamin C are uncooked pumpkins and other winter squash, sweet potatoes and leafy dark greens.

Vitamin E is necessary for the normal functioning of the immune and reproductive systems. Vitamin E is concentrated in polyunsaturated fats, such as those found in seeds and whole grains, as well as in fresh cod liver oil, corn oil, soybean oil and wheat germ oil. Dietary deficiency most often results from feeding oil-rich rations that have gone rancid, which can occur rapidly when the temperature and humidity are high (see “Free Radicals and Rancid Fats” to the left). Vitamin E and the trace mineral selenium are closely linked. An adequate amount of vitamin E in the diet ensures the metabolism of sufficient selenium.

Selenium is an important antioxidant that, working together with vitamin E, helps maintain the immune system, as well as being essential for the proper development of muscles, nerves and the circulatory system. Fishmeal and dried brewer’s yeast are good sources of selenium, as are any crops grown in the naturally selenium-rich soils of the plains in the United States and Canada.

A chicken hides in a tomato plant. Overripe tomatoes are nutritious antioxidants for chickens.

Super Antioxidant Lycopene

Lycopene is a particularly efficient antioxidant. It is one of several naturally occurring pigments known as carotenoids, and is responsible for the color of tomatoes, watermelons, and a few other red fruits and vegetables. Lycopene-rich produce, fed to layers, deepens yolk color and improves shell thickness and hardness, making eggs less prone to breakage. Evidence suggests that lycopene may improve sperm production in breeder cocks. And chicks that come from lycopene-rich eggs experience less oxidative stress at the time of hatch. In any chicken, lycopene protects cells from damage caused by free radicals. It is especially beneficial in helping prevent the tumors that plague older chickens.

During hot summer weather, a lot of chicken keepers reduce heat stress by feeding their chickens chilled or frozen watermelon. Not only does the coldness of the fruit help dissipate a chicken’s body heat, but the fruit’s lycopene reduces the effects of oxidative stress and antioxidant depletion resulting from heat stress.

Tomatoes and tomato products are especially high in lycopene. During the summer, an excellent source of lycopene for chickens is excess or overripe tomatoes from your garden, as well as scraps resulting from salad making or canning. In winter, home canned tomatoes are an even better source, since processing by heat changes lycopene into a form the chicken’s body cells can more readily use.

As an added bonus to feeding tomatoes and watermelon to your hens, when you eat the resulting eggs, their lycopene-rich yolks contribute this powerful antioxidant to your own diet. In improving the health of your chickens, you’re improving your own health as well.

The best way to control free radicals and reduce the risks associated with oxidative stress in your chickens is by treating them to a variety of antioxidants in the form of a balanced diet rich in colorful fruits and vegetables. Especially beneficial are fruits and vegetables from a source that does not use chemical fertilizers and pesticides or, better yet, grown in your own organic garden.

Gail Damerow is author of The Chicken Health Handbook — newly revised, completely updated, and available from our bookstore at


Chickens need some amount of fat for health and growth. A chicken’s body uses fat to store energy and fat-soluble vitamins, to insulate body tissues, and to cushion internal organs. Too much fat, however, can result in reduced health, laying, and fertility.

Fat consists of a group of compounds called fatty acids, which are divided into two main types: saturated and unsaturated. The latter is further subdivided into two types: monounsaturated and polyunsaturated.

Polyunsaturated fatty acids, in turn, are divided into two main groups: omega-3 and omega-6.

A chicken’s body can metabolize nearly all the fatty acids it needs from normal daily rations. The single exception is the omega-6 fatty acid known as linoleic acid, which is required for both growth and egg production.

Linoleic acid comes from nuts, seeds, vegetable oils and animal products. Animal sources include pork lard, beef tallow, and milk. An excellent nonanimal source is sunflower seeds. Linoleic acid is concentrated in polyunsaturated oils, such as safflower oil, sunflower oil and corn oil.

The problem with using polyunsaturated oils is that they can get rancid pretty quickly, especially when exposed to air, heat and light. Rancid oils are unstable and create free radicals. Refined oils have been exposed to air, heat, and light during processing and therefore get rancid more quickly than the whole seeds they came from. If you choose to add oil to your chickens’ rations, store it in a cool, dark place and mix the oil into only as much ration as you will immediately feed your flock.

— Gail Damerow

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