adapted from article by Lawton Stewart, Ph.D.
Vitamins are a unique dietary component for beef cattle and are categorized into two groups: water-soluble and fat-soluble. Bacteria in the rumen synthesize water-soluble vitamins (e.g. B12, thiamin, niacin). Therefore, supplementation is generally not needed as long as the rumen if functioning properly. This leaves the fat-soluble vitamins (A, D, E, and K). Of these, Vitamin A is considered the most important when feeding cattle.
What is Vitamin A and why is it important?
Vitamin A, also known as retinol, is a compound that is essential for growth, reproduction, maintenance of body tissue, and bone development. Technically, Vitamin A is not found in plant material; rather, the precursors carotenes and carotenoids, are present in various forms.
Where is Vitamin A found, and can the body store it? Except for corn and corn byproducts, most grains and commodity feeds will not provide an appreciable amount of Vitamin A. The major source for cattle is fresh forage. However, Vitamin A is rapidly degraded by heat and sunlight, therefore hay is much lower in Vitamin A compared to fresh forage. Additionally, as forage matures and/or becomes drought-stressed, the Vitamin A content will decrease. Ensiled forage (silage and baleage) does lose some Vitamin A, but not to the extent of hay. A recent study evaluated the Vitamin A content of several common feedstuffs used for cattle and are presented in Table 1.
What are the signs of deficiency and how are they caused?
A major function of vitamin A is associated with vision, specifically with the transition from light to dark. Therefore, night blindness is a key symptom to identify a vitamin A deficiency when other symptoms are also present. Symptoms of deficiency:
- Night blindness
- Decreased reproductive performance
- Skin and hoof lesions
- Skeletal deformation
Deficiency symptoms are most likely to occur from one or more of these feeds
1. Feeds that have received excess exposure to sunlight, air, and high temperatures.
2. Hay harvested from drought conditions.
3. Feeds that have been stored for long periods of time. 4. Feeds that have been heavily processed.
5. High-concentrate diets (e.g. finishing rations).
How much Vitamin A do cattle need?
The daily requirement for beef cattle is presented in Table 2. The requirement increases as cattle mature and is greatest for lactating cows. Fortunately, the liver can store Vitamin A, and this storage can serve to prevent a deficiency. Typically, this storage can last two to four months. However, the storage can be variable and cannot be accurately assessed without a liver biopsy.
Based on the amount of Vitamin A in fresh and ensiled forage, the requirements of all cattle are met. However, when feeding hay, the requirement is not met. Moreover, it can be assumed that drought-harvested hay or last year’s hay will not contribute any Vitamin A.
What are supplementation options?
The simple solution is to provide a mineral that provides adequate Vitamin A. Most minerals do contain a vitamin pack, but the question becomes, “is it enough?” Many times, it is assumed that just as long as it is included, it should be adequate.
The last column of Table 3 gives the amount of Vitamin A needed in a mineral mix (i.e. what is listed on the tag) to meet the requirement with an additional 10% as insurance. This amount changes significantly based on the feeding program, and each producers will have a unique situation.
See the full article and additional info from University of Georgia Beef Team here.
Your next read: Emergency USDA Funding Available to Protect U.S. Livestock and Animals from New World Screwworm
