Editor’s note: The following answer is provided by Bill Weiss, professor of animal science at The Ohio State University.
Q: What are the updated recommendations for vitamins?
A: Vitamins add cost to the diet, but when supplemented appropriately, they will increase income over feed costs and improve cow health.
Vitamin A is among the least stable vitamins, and loss of activity can be approximately 10 percent per month depending on storage conditions. In addition, potency can vary among sources of supplemental vitamin A. This uncertainty justifies a small safety factor (10 percent or 20 percent excess). One study reported that feeding vitamin A at about twice the NRC recommendation increased milk yield. Therefore, supplementing vitamin A at 1.1 to 2 times the NRC recommendation (e.g., 80,000 to 150,000 IU/day for Holstein cows) can be justified, but supplementation in excess of 150,000 IU/day is not supported by current data. Indeed, one study reported a significant decrease in milk yield when early lactation cows were supplemented with about 550,000 IU/day.
The current recommendation for vitamin D is adequate with respect to calcium metabolism, but we now know that vitamin D has a multitude of functions in addition to calcium homeostasis. Studies with humans and limited research with bovine cells have shown that vitamin D has important roles in immune function and that blood concentrations of 25-hydroxy (OH) vitamin D (humans) required for maximal immune response was greater than concentrations required for optimal calcium metabolism. Infusing 25-OH vitamin D into experimentally infected (E. coli) mammary glands reduced clinical signs of mastitis and reduced bacterial counts. Dairy cows housed inside without exposure to sun and fed vitamin D at NRC recommendations had significantly lower plasma concentrations of 25-OH vitamin D than cows fed no supplemental vitamin D but housed outside in the summer with extensive sun exposure. We do not know the optimal concentration of plasma 25-OH vitamin D, but current supplementation rates do not provide for maximal concentrations. Much more research is needed on vitamin D, but circumstantial evidence suggests benefits from increasing supplementation up to 2 times the NRC recommendation or ~40,000 IU/day.
No new data are available refuting current NRC requirements for vitamin E except during the prefresh period. Increasing vitamin E intake to 2,000 and 4,000 IU/day during the last 14 to 21 days of gestation (i.e., the prefresh group) can help reduce mastitis, retained fetal membranes, and perhaps metritis. New data suggest over-supplementation for the entire dry period (3,000 IU/day) may be a risk factor for mastitis and should be avoided.