by: Stephen B. Blezinger
Ph.D., PAS

Part 2

In the last issue we began our discussion on the necessity of vitamins in cattle diets. We looked at Vitamin E at length and discussed the importance of this compound in the animal's diet and requirements and feeding rates. As a nutritionist I have always found it interesting how the nutrients required in the smallest amounts can have such a profound effect on performance and health in the animal.

The following takes a similar look at Vitamin D. As mentioned in Part 1, Vitamin D or D-3 as it is often called, in many cases, is given less importance in many producers minds because we have been told that it is produced in the skin as a reaction to exposure to sunlight. For cattle that spend most of their lives outside in the sun, it is generally assumed that they can manufacture all they need. This may not be entirely true. Especially in today's high performance demand production environments. Research has shown that added, supplemental levels of Vitamin D can be advantageous to animal performance.

Some basics for Vitamin D

Vitamin D play's a variety of roles in the animal's body. These include:

Beginning very early in life it plays a significant role in skeletal development.

Vitamin D increases the absorption of calcium (Ca) and Phosphorus (P) from the digestive tract and overall metabolic use. This includes movement of Ca and P into and out of storage tissues as required.

One of the most important roles is the regulation of blood calcium levels as well as the conversion of inorganic to organic P and its incorporation and use if a variety of tissues. An example of this is D's involvement in the process that incorporates P (phosphorylation) into carbohydrates which is part of the energy metabolism process.

It has a regulatory role in immune cell function.

Vitamin D aids in the formation of sound bones and teeth where it is involved in osteoblast (bone cell) formation and calcification.

Its specific role in the prevention of rickets in young animals or osteomalacia in mature animals is associated with its involvement in the metabolism of calcium and phosphorus.

There are two primary forms of vitamin D:

1) Ergocalciferol (vitamin D2) derived from the plant steroid, ergosterol. Ergosterol, found in green plants is converted to D2 when the plant is harvested and cured in sunlight. So hay that has been properly cured and baled will provide a good source of D2. However, hay that is not properly cured (over or under cured) will not contain adequate D2 simply because the compound will have been damaged or destroyed.

2) Cholecalciferol (vitamin D3), which is found only in animal tissues or products. The compound, 7-dehydrocholesterol, a sterol found in the skin of animals is converted to vitamin D3 by ultraviolet rays of sunlight.

The sources of vitamin D vary in their activity in different species of food animals. Both vitamin D2 and D3 are biologically active for cattle, sheep, goats and swine D3 is the most commonly supplemented form. Vitamin D3 is about 100 times as active as D2 for poultry so again it is the most commonly supplemented form.

Vitamin D is easily and cheaply supplemented in cattle feeds, minerals and other supplements. It is routinely provided in most programs. Many commercial products of vitamin D are sold in concentrated form for inclusion in supplements.

Vitamin D may also be injected in combination with Vitamin's A and E. This is a fairly common practice in weaned and newly received cattle if growing and feedlot operations where the nutritional history is not known.

Vitamin D status can be assessed by sampling and analyzing blood serum concentrations of 25-hydroxycholecalciferol. Adequate values are 2050 ng/mL, with concentrations <5 ng/mL indicating deficiency.

Requirement Differences

Young, growing animals have a greater requirement for Vitamin D than mature animals. This is largely related to their rapid growth both structurally (skeleton) and other tissues. As mentioned previously, under normal conditions, cattle receive adequate vitamin D from exposure to direct sunlight or from consumption of three to four pounds of sun-cured forages daily. For young calves, cow's milk should also provide an adequate source of vitamin D. So a combination of these sources should be more than adequate to meet the requirements of the young animal, depending on circumstances. Experiments with calves have indicated a requirement of approximately 300 I.U. of vitamin D per 100 pounds of body weight.

In general, regardless of animal class, the vitamin D requirement of beef cattle is 125 IU/lb of diet dry matter. For mature cows consuming 24 lbs of dry matter, this would equal a daily intake of 3000 IU of vitamin D.

Deficiency Symptoms

A well-known, common vitamin D deficiency symptom in young animals is a condition known as rickets. Rickets is characterized by soft, porous, poorly developed bones. Early signs of vitamin D deficiency in calves are poor appetite, decreased growth, stiff gait, weakness and labored breathing. Later signs include swollen joints, slight arching of back, bowed legs and bent knees.

Bones fragility is another sign of a D deficiency. This is a symptom in young and older animals alike.

Finally, a deficiency in pregnant animals may result in dead, weak or deformed calves.

Additional Benefits

Providing additional, supplemental vitamin to the diet may have additional benefits aside from meeting basic physiological requirements. In dairy cattle, recent research has shown that mastitis levels may be reduced with additional feeding and in some cases infusion of vitamin D directly into the udder. Mastitis, a common and costly disease, affects the mammary gland (infection) of cattle, resulting in a decrease in milk production and quality. In some cases, infected cows have to be removed from the herd. Economic losses are estimated at $2 billion a year in the dairy industry. It is possible for beef cows to likewise be affected by mastitis but often goes undetected and results only in a reduction of milk production to the calf. Feeding additional vitamin D may be helpful in reducing or eliminating mastitis. This response may be indicative of a stimulatory effect to the immune system not only of the mammary gland but to the animal as a whole.

In recent years, some work has shown that feeding of increased levels of vitamin D, for the last 3 to 4 weeks of the finishing period in slaughter cattle has resulted in improved meat tenderness. A potential concern is that the elevated levels of D may have adversely affect beef flavor.


Vitamin D is a critical to animal nutrition as are all the vitamins. The ability of the animal to produce its own D is certainly a benefit and reduces the need for supplementation. Vitamin D should, nonetheless, be fed at recommended levels for all classes of cattle.

In Part 3 of this series we will take a look at Vitamin A, the most highly researched of the fat-soluble vitamins.

Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at For more information please visit us on Facebook at Reveille Livestock Concepts.

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