Vitamin A is an essential nutrient for humans and cattle alike. Our ruminant counterparts convert beta carotene found in plant leaves into vitamin A, which is necessary for vision, immune function, and bone development of calves.

Garland Dahlke, a research scientist with the Iowa Beef Center at Iowa State University, says cattle consuming fresh forage can readily store vitamin A in body fat and in their livers. These reserves can meet the needs of a cow for several months. Dry hay, on the other hand, provides much less vitamin A because beta carotene declines relatively quickly in stored forage.

For example, research shows vegetative tall fescue contained over 20,000 micrograms of beta carotene per gram (mcg/g) of dry matter. After forage was harvested and stored for six months, this number dropped to approximately 800 mcg/g.

Dahlke says a similar — if not greater — decline in beta carotene can occur in cornstalks prior to baling. In addition to the length of storage, the exposure to sunlight, heating, and weathering will further reduce beta carotene and vitamin A levels in bales.

A greater risk

Vitamin A deficiencies may be more prominent in areas that experienced a dry summer this year. Drought conditions inherently reduce beta carotene concentrations in pasture plants, and Dahlke notes limited forage growth may have led farmers to start feeding hay during the grazing season. This would have reduced animals’ ability to accumulate vitamin A from fresh forage, leaving them with low reserves as they enter the winter.

Signs and symptoms of vitamin A deficiency include reduced feed intake, rough hair coat, diarrhea, and a higher susceptibility to infection. There is also a greater frequency of retained placentas after birthing, and calves born to cows with low vitamin A reserves have a higher chance of developing scours and weak calf syndrome.

To ensure the health of cows and calves, supplementing hay with vitamin A is key to avoid deficiencies. Dahlke recommends providing 1,270 international units of vitamin A or 3,175 micrograms of beta carotene per pound of dry matter fed.

Since vitamin A is primarily transferred from cows to calves through colostrum, it is recommended to start supplementing animal feed at least 45 days prior to calving. Then, continue to provide the nutrient through early lactation.