Vitamin A & Forages

While we often focus on the importance of knowing the energy and protein value of a forage, mineral and vitamin balances can be an equally crucial component of diets. Understanding all the mineral balances and interactions in a ration is well beyond the scope of this segment, but today we are going to look at some new research from UNL on Vitamin A.  Vitamin A is one of those micronutrients that when out of balance can cause big issues, especially in new calves.  Proper levels of Vitamin A are vital to the proper development of a strong immune system in newborn calves, although calves themselves are born with no Vitamin A stores at all. All their initial Vitamin A comes from a cow’s colostrum.  So, making sure our cow is not deficient in Vitamin A during late gestation when colostrum is forming is important.  Without it, we are setting our calves up for a difficult start to life and more than likely, reduced overall performance later on.

Hannah Speer, UNL Animal Science PhD student and Mary Drewnoski, UNL Beef Systems Specialist have been looking into how Vitamin A is provided to a cow through her diet. In many cases, meeting a cow’s requirement for Vitamin A isn’t a big issue.  Vitamin A is produced by the cow from β-carotene, which is found in abundance in green forage, and stored for use later in the year when dietary levels are restricted. 

At these restricted periods of time, some dietary Vitamin A is still important.  When dietary Vitamin A is low, stored reserves cannot be fully accessed. Stored forages that are still green in color (high quality alfalfa or grass hay, well packed and fermented silage, etc.) can still contain moderate levels of β-carotene, and thus provide some additional Vitamin A to diets during the winter months.  Additionally grains or grain byproducts can provide a mineral source of Vitamin A to a diet. In these situations, where summer grazing has filled reserves and diet is providing an additional source, a cow needs 36,000 IU/d at late gestation and 51,000 IU/d during lactation.   

The issue comes when cattle have been away from green forage for a while and are unable to build up reserves during the summer.  This occurs most often during long term confinement situations but may be an issue during prolonged drought periods as well when green grass is hard to come by.  In these scenarios, pregnant cattle may require up to 86,000 IU/d and lactating animals up to 128,000 IU/d.  If you have animals in a similar situation, a closer look at your Vitamin A supplementation may be warranted. 

It’s important to note that Vitamin A degrades when exposed to heat, light, or moisture.  So, if you plan on stocking up on mineral, do so during the winter months when temperature is going to be less of an issue.  Store your mineral in a dry place and keep it out of the sun.  In cases where a custom mineral may be required to meet especially high Vitamin A demands such as long term dry-lotting, it may be worth cutting out additional mineral features that are often included in prepackaged minerals, such as those that improve weatherization.  Since mineral will be fed daily as part of a ration, these additions aren’t needed and cutting them out can save on costs.

Vitamin A is a critical component to cattle diets, especially for calf health.  When diets lack green forage, demand will increase and calf health can suffer if we don’t correct the imbalance with additional supplementation.

-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce.  He is based out of the Cedar County Extension office in Hartington.  You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu .