The Role of Vitamin A in Ruminant Nutrition

CRYSTALYX® Brand Supplements

As you have probably already heard, a global vitamin shortage (particularly vitamin A) has sky rocketed feed prices and set the feed industry on edge. This shortage is expected to continue well into 2018.  As a result, many feed manufacturers have taken steps to reduce vitamin levels, particularly vitamin A, in their products. But is that a good idea? This article seeks to discuss the importance of vitamin A in the ruminant diet and explore the pitfalls of cutting vitamin A out of the diet or storing supplements or feed for long periods.

What is Vitamin A and What Does it Do?

Vitamin A, or retinol, is a colorless, alcohol compound. Vitamin A is one of the fat-soluble vitamins (along with vitamins D, E and K). Vitamin A is necessary in ruminants for many functions including:  vision, bone growth, immunity and maintenance of epithelial tissue. Vitamin A deficiency results in night blindness and formation of ulcers on the cornea. Vitamin A affects bone development through bone metabolism. Essentially, Vitamin A deficiency results in unchecked bone growth that manifests as malformed bones and joints. Vitamin A directly affects immunity through both production of antibodies and through maintaining an adequate barrier to infection with healthy epithelial cells. Vitamin A deficiency reduces the primary antibody response in the event of infection.

Additionally, vitamin A’s role in the maintenance of mucous membranes and epithelial linings directly affects other production parameters. Deficiency often results in keratinization (a form of thickening and hardening of tissues) and thus a loss of tissue function and increased susceptibility to infection. Keratinization of the digestive and respiratory tracts results in diarrhea and pneumonia. These are typical secondary symptoms of vitamin A deficiency. Keratinization of the reproductive tract results in poor sperm production in males and early abortion in females.

How Do Ruminants Get Vitamin A?

Ruminants get vitamin A solely through their diet, either from man-made supplements or from plants. Plants make carotene which the ruminant then converts into vitamin A. Plants contain carotene to varying degrees. A relatively good indicator of carotene content is the amount of greenness of the plant. Fresh forages and early cut, leafy, green hays have high carotene content. Cereal grains (excluding yellow corn) have poor carotene content. While yellow corn has more carotene than other cereal grains, its content is only one-tenth that of well-cured quality hay.

Ruminants on high-grain diets and/or do not have adequate access to green growing forages are most susceptible to vitamin A deficiencies. This is most common during winter months when forages are dormant, but also in situations of overgrazing or drought too.

Vitamin A is stored in the liver and can be built up during times of abundance to help animals cope during scarce periods. It is believed that healthy adults can store vitamin A to last several months. Young animals have much less storage capacity. Borderline deficiency is much more common than severe deficiency and the need for vitamin A is greatest during calving (kidding or lambing), breeding and other times of stress.

Vitamin A Instability

All sources of vitamin A are relatively unstable and degrade over time. The carotene content of cut hay decreases during the curing process and then the content of the cured hay decreases during storage. The amount of degradation depends on temperature during storage, exposure to air and sunlight, and amount of time in storage. Under average conditions, the carotene content of hay can be expected to drop roughly 6 to 7% per month. Thus, hay that is over 6 months old has lost at least half of its vitamin A activity. The vitamin A content in commercial feeds and supplements also decreases over time (see Tables 1 and 2). Generally, a loss of over 50% over one year is common and losses greater than 50% in 6 months are possible. For this reason, it is important to only purchase enough feed or mineral/vitamin supplements that can be consumed within 6 months or less. Talk with your feed manufacturer for specific storage recommendations on the products you are utilizing.

Why Cutting Vitamin A Levels Isn’t Always the Answer

In the past, we’ve never worried about vitamin A degradation in feeds and supplements as a rule. Vitamin A was relatively cheap and we over-supplemented in many cases. Thus, even with a loss of vitamin A activity, our animals were getting plenty. Now that vitamin A prices have skyrocketed and supply is short, we need to be more mindful of what we are delivering and when.

Cattle vitamin A needs are highest during stressful periods like calving and lactation. Given that many of our cattle calve before green grass is abundant, it is critical to supplement these cows with adequate vitamin A through pregnancy and lactation. Once pastures are green and lush again, one can safely cut back on supplemental vitamin A. But until then, you are placing your herd at risk.

Summary

Even with the high cost of vitamin A right now, the extremely high cost of lost production from lack of vitamin A makes continued supplementation during winter months still important. If one wishes to cut back, do so after spring green up when plenty of new forage is available. CRYSTALYX® Brand Supplements is an excellent delivery method for all nutrients providing continuous nutrient availability. CRYSTALYX® offers a wide range of self-fed supplements to match and supplement a variety of forage qualities and feeding programs. 

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