Vitamin A plays a critical role in young calf health. Calves are born with very limited vitamin A stores because little transfers from the dam during gestation. Newly born calves rely heavily on colostrum for their supply of vitamin A, making the cow’s late-gestation diet critically important. Milk is a poor source, so calves depend on the colostrum for their Vitamin A supply for the first few months of life.
For most herds calving in late winter or spring, cows are fed stored or stockpiled forages during their last trimester. Recent research suggests that late gestation cows need 75,000 to 90,000 IU/d of vitamin A, but the amount of vitamin A in hay varies widely. Factors such as forage type, maturity at harvest, haying and storage conditions, as well as how long hay has been stored influence vitamin A levels. This can mean supplementation needs range from none at all to nearly the full requirement coming from a supplement.
Color Can Be a Clue
Greener hay generally contains more beta-carotene, and therefore more vitamin A, than bleached or weathered hay. It’s not a perfect measure, but it can give you a quick indication. To make this more useful, Nebraska Extension developed a set of hay samples with known vitamin A content so you can visually compare your hay to them.
See and Compare at Upcoming Events
Nebraska Extension have these reference hay samples on display at the GSL Open House on August 20, 2025 and Husker Harvest Days at the “Big Red Building” on September 9-11.
At these events you can:
- Visually compare your hay to our reference samples.
- Get a better idea of whether you may need to boost vitamin A in your winter mineral program.
- Talk to experts to get nutritional advice and your questions answered.
Help Our Research – Bring Your Hay Samples
Nebraska Extension is working to develop a tool that would allow you to take a picture of your hay and get an estimate of the vitamin A content, but we need more samples. Bring a sample of your hay to either event and we’ll add it to our research analysis. Your sample will help us better serve beef producers in the future.
