Vitamin A is rarely a concern in range cattle nutritional programs because it is readily synthesized from carotene, which is common in green growing plants. However, in drought situations where plants become dead or dormant, the carotene content becomes practically devoid and may lead to a deficiency of the precursor to vitamin A. Carotene levels are low in mature, weathered forages, grains and many crop residues. It is also lost in stored hay crops over extended periods of time.

Therefore, if hay that was stored throughout all of last fall and winter is to be fed in the upcoming winter, the vitamin A content will be considerably less than when that forage was originally harvested. In addition, some scientists have suggested that high nitrate forages common in drought years can exaggerate vitamin A deficiencies.

Deficiencies of vitamin A usually show up first as weak, blind or stillborn calves. Other signs are scours, respiratory problems, poor gains and poor reproduction.

Fortunately, the liver of an animal is capable of storing vitamin A for long periods, and frequent supplementation is not necessary. A singular injection of one million International Units (IU) of vitamin A provides sufficient vitamin for two to four months in growing and breeding cattle.

Because the daily requirements of beef cows range from 30,000 to 50,000 IU-depending on size, stage of production, and level of milk production-supplements can be fortified with vitamin A to supply the minimum daily requirement.