Topics Ask an Expert Register Me Links Home Vitamin A and the Preweaned Calf Vitamin A deficiency presents a special risk with the young calf. Because little of the vitamin is transferred from the dam to the fetus during gestation, practically all calves must be considered vitamin A deficient at birth. Researchers have reported that in fetal calves, liver stores, which are the most sensitive measure of vitamin A status, are about 1 percent of the levels found in adult cattle. Colostrum generally provides the newborn calf with a rich initial source of vitamin A and the carotenoids that can serve as vitamin A precursors. However, concentrations decrease logarithmically as the mammary secretions change to normal milk.
Low levels are especially likely when cows receive inadequate vitamin A supplementation.
Once the preruminant calf has developed initial tissue stores of vitamin A from colostrum, it is important to ensure that adequate intake continues to maintain and increase vitamin A stores. A requirements from the diet. A fortification beforehand, an infection in these animals could severely diminish body stores of vitamin A and compromise health and performance. Even in this later work, the calves could not truly indicate preruminant needs, since they were almost nine weeks old at the start of the study and consuming calf starter and chopped alfalfa hay. There are also questions about the NRC recommendation because environmental stress, disease and other factors can significantly increase vitamin A requirements.