Cattle exposed to winter feed are susceptible to vitamin A deficiencies. In most cases, early spring grass will contain fairly high levels of carotene (precursor to vitamin A) and will adequately meet the cow's requirement. Ensiling effectively preserves carotene but the availability of carotene from corn silage may be low.
Vitamin A can be supplemented in the mineral mix or by an injection. One million International Units of vitamin A palmitate intramuscularly or intraruminally when cows are palpated for pregnancy will meet their vitamin A needs for two to Four months (Wagner and Goetz, 1989). In the mineral, add 10,000 to 50,000 International Units per 0.1 to 0.2 lb of mineral mix. Be very cautious if you are mixing your own vitamin-mineral mix. Only a very small amount of vitamin A premix is needed, and mistakes in mixing can lead to toxicity situations. Vitamin A will not remain stable very long in homemade mineral mixes (approximately two to three weeks). Utilize or request protected forms of vitamin A for your vitamin-mineral mix.