In the early 1900s vitamins were discovered. Scientists were able to isolate a vital substance, or “vitamin”, that was required in the diet of animals and humans. As the first vital substance it was called vitamin A. However, vitamin A deficiency and reported cures are alluded to in the bible and ancient Egyptian texts suggesting the use of cattle and poultry livers as a cure for eye disease. As it turns out vitamin A is a fat soluble vitamin stored in the liver and is required for normal vision.
Vitamin A is required for a host of body functions but rarely consumed by cattle. Instead, as herbivores cattle consume forages or forage products containing carotenoids which have a structure similar to vitamin A. These compounds are converted to vitamin A in the liver and distributed throughout the body. Green leafy plants are higher in vitamin A than corn silage, grains, and other concentrate feeds. This is the reason grass-fed cows contain yellow fat and feedlot animals have white fat. The higher level of carotenoids in the forage are pigmented and stored in body fat.
Carotenoids and vitamin A are not particularly stable compounds and readily degrade with exposure to moisture, heat, and light. Consequently, conditions encountered while storing harvested feeds can decrease the amount of functional vitamin A precursors. However, environmental conditions leading to the storage of visibly high-quality forages are generally adequate in vitamin A. Over time as the color and other nutrients fade from stored hay so does vitamin A. Vitamin A and three-year-old hay do not mix.
Deficiency of vitamin A affects all epithelial layers including skin, the eye, the respiratory tract, the reproductive tract, etc. Animals become more prone to pinkeye, skin disease, urinary tract infections, respiratory disease, decrease conception, and decreased sperm production. Vitamin A is also involved with the function of many hormones and can alter the expression of some genes. Affected cattle are unthrifty and have decreased rate of gain.
Vitamin A can be supplemented in one of three general ways; as part of a concentrate, free-choice mineral, or injectable product. The vitamin A content of range cake and other pelleted supplements is questionable due to the high heat created by extrusion. Mineral packages with vitamin A require coated vitamin A to avoid contact with the trace minerals that can cause damage to the vitamin structure. Injectable formulations are effective but generally viewed as unhandy as timing is important with regards to stage of production and other biologicals being administered. Often times more than one source of vitamin A is used to provide adequate supplementation when needed.
Cows are beautiful creatures that create a delicious meat protein from the refuse of non-arable lands. The unusually large area suffering from drought has created a feed shortage. Cows will be asked to produce while being fed marginal feeds this year in particular. As you dive the loader bucket into the three-year-old stack with nary twine, remember your cows will need supplemental vitamin A.
Nyctalopia – night blindness resulting from a loss of functional rhodopsin during vitamin A deficiency.F