Vitamin A in Cow-Calf Operations
By Dr. Steve Ensley
Vitamin A is necessary to ensure animal health in cow-calf operations. Vitamin A production at a BASF plant in Germany in October 2017 was disrupted due to a fire. Production returned to normal in 2018, but there are still potential vitamin A shortage problems.
Cattle convert beta carotene from green vegetation into vitamin A. In a normal pasture season, the daily intake of carotene that is converted into vitamin A is three to five times the requirement. Cattle can store up to four months of vitamin A in the liver during this period. Under ideal conditions cattle feed good quality hay during the winter will maintain adequate vitamin A status.
When we have drought, as we had during the summer of 2018, the available carotene in the forage will be below normal levels. Therefore, whether the cow is grazing dry grass or consuming hay made from drought stressed forages, her vitamin A intake will likely be low. Even when hay is made from good green forages, the carotene is not very stable and will decrease over time even when the hay is stored inside.
There is concern for the 2019 spring calving season that vitamin A stores in pregnant beef cows will be low.
Common clinical signs of vitamin A deficiency can vary widely, including educed feed intake, reduced growth, night blindness, edema, diarrhea, low conception rates, abortions, and stillborn or weak calves. Calves born to cows deficient in vitamin A may have trouble mounting a normal immune response.
Without supplemental vitamin A, the vitamin status of cows will decrease over the winter and potentially become deficient. There is a wide level of bioavailability for vitamin A in mineral/vitamin supplements. Even if you are feeding a good quality mineral/vitamin supplement, animals may not be absorbing an adequate amount. Feed with elevated nitrate concentrations will also interfere with vitamin A absorption, another compounding factor during a drought. Vitamin A concentration will decrease over time, so vitamin A supplements should be stored for short periods (e.g. not bought in the fall and kept until spring).
Cows need 30,000 to 50,000 IU of vitamin A/hd/day. Injectable vitamin A is a quick method of returning the cow’s vitamin A status back to normal. 1.5 million IU of vitamin A are needed for an adult cow. If severely vitamin A deficient, monthly injections may be needed.
Newborn calves obtain the majority of their vitamin A by ingestion of colostrum. Very little vitamin A is transferred across the placenta, unlike other minerals and vitamins. Calves born to vitamin A deficient cows may need a parenteral injection of vitamin A. Newborn calves require 500,000 IU of vitamin A.
For diagnostics you need a 1 ml serum sample to assess serum vitamin A status. An adequate number of cows in all the production classes of young heifers to older cows need to be sampled. Liver from calves that have nursed can be used to evaluate vitamin A status. If a calf did not nurse a liver sample will not be helpful to determine vitamin A stasis. If low vitamin A status is a concern it should be addressed prior to calving to ensure the calves are healthy and able to respond to the environmental stress in the spring.