In bovine health, much like our own, we defend against free radicals with antioxidants
All animals require antioxidants. The effectiveness of alpha tocopherol “vitamin E” as an antioxidant is associated with the prevention of cell degradation (technically: lipid peroxidation) in animals.
However, a few researchers have interpreted the low peroxide level of tissue lipids in animals receiving supplemental E as due to the inhibition of absorption of oxidized fatty acids from the intestinal tract.
Suffice it to say that vitamin E is the principle membrane-associated antioxidant molecule in mammals. It plays a major role in preventing oxidative damage to cell membrane lipids by scavenging free radicals.
I could stack up some more 50-cent words to explain the various chemical properties of vitamin E, and that might intrigue biochemists, but let’s just say that the many flavors of vitamin E are sort of like socks: even if they are miss matched, they still fit and work as socks.
Absorption and transport
Vitamin E is hydrophobic and is absorbed similarly to other dietary fats-lipids. If you need to feed high levels of vitamin E, you want to ensure adequate fat in the diet—otherwise vitamin E absorption is reduced.
After solubilization by bile acids, vitamin E is absorbed in the small intestine. It moves into the blood stream from there.
Once in circulation, much of the vitamin E is taken up by the liver and repacked into very low density lipoproteins, then pushed into blood to circulate through the animal’s vascular system. Ultimately, vitamin E is transported in blood bound to a variety of lipoproteins, from which it is taken up by tissues throughout the body. Vitamin E is stored within energy-storing fat.
The claim to fame of vitamin E is as an antioxidant. In other words, it is a scavenger of free radicals. Free radicals are generated by numerous processes within cells and have the ability to damage cell membranes, proteins and nucleic acids.
Vitamin E is at the forefront of the body’s homeland security defense forces to prevent oxidative damage by free radical terrorists. Due to its fat solubility, vitamin E is particularly important in protecting cell membranes.
Vitamin E levels in manufactured feeds
An ongoing discussion is how much vitamin E should be fed. There is a difference between nutrient requirements and nutrient recommendations. The requirement is the quantity the animal needs to prevent nutritional disease; the recommendation is the amount that we target to feed based on the current objectives. Because some things seem to work better, say feeding 1,000 units of E to dry cows, we often recommend the practice.
For dry cows on vegetative grass pastures, diet vitamin E content will be very high, well exceeding animal requirements. So you might wonder why I’d recommend additional vitamin E in the diet. I’d make the recommendation because things go better when we feed 1,000 units of E to dry cows compared to feeding 0 units. It’s an ounce of prevention and pound of harm scenario.
In the 1980s, it was fairly common to daily feed about 300 units of vitamin E to milk cows, and 10 to 50 units to beef cows.
Now days we often see milk cows and finishing cattle take 1,000 units of E per day, while beef cows and growing cattle get about 50 to 100 units.
The vitamin E load on dry milk cows will vary from none to 8,000 units a day, with the expected level closer to a tick over 1,000.
To demonstrate this effect, consider the trial done by Dr. Weiss and colleagues at Ohio. They held selenium constant at 0.1 ppm, then fed dry dairy cows different levels of vitamin E, measuring incidence of mastitis.
Deficiency and toxicity
Vitamin E deficiency has been associated with a number of problems:
• Impaired fertility
• Muscle disease, nutritional myopathy (white muscle disease)
• Degeneration of central nervous system and peripheral nerves
• Accelerated destruction of blood cells
There are any number of reports that have fed cows thousands of units of vitamin E a day for months at a time. The current calculations are that chronic vitamin E toxicity in dairy cows would to be at least 80,000 units a day for weeks on end. That corresponds to 4 pounds per day of vitamin E 20,000. To kill a cow with vitamin E, the way to whack her with the smallest requisite amount of vitamin E, would likely be to drop a pallet of vitamin E on her head.
All MFA manufactured feeds, other than commodity blends #44131 or #44161 are fortified with vitamin E.
Dr. Jim White is ruminant nutritionist for MFA Incorporated.