Slow pasture growth due to drought conditions limits more than forage yield and grazing potential — it can reduce beta carotene levels in plants and raise the risk of vitamin A deficiencies in cattle. An early start to the hay-feeding season when fall pastures fizzle out may also warrant more diligent vitamin A supplementation to ensure cows meet their needs this winter.
In an article from Kansas State University Extension, Emma Briggs says vitamin A deficiencies can result in reduced feed intake, slow animal growth, and reproductive issues like low conception rates and stillborn calves. Moreover, calves born to cows with vitamin A deficiencies can have depressed immune systems, putting them at greater risk for diseases like scours and weak calf syndrome.
It starts with beta carotene
Beta carotene is the precursor to vitamin A and is abundant in fresh forage. In fact, cattle grazing lush pastures during the growing season can consume enough beta carotene to meet five times their vitamin A requirements. Cattle can also store excess vitamin A in their livers for up to four months. But deficiencies arise when pastures go dormant, hay is fed, and those biological reserves are depleted.
“By the end of the summer, cattle typically store ample vitamin A in their livers, but without supplementation during the winter, deficiencies can develop,” says Briggs, a beef systems extension specialist. “Cows grazing dry, brown grass or consuming hay made from drought-stressed forages are likely to have low vitamin A. Even hay from good-quality, green forage may not maintain adequate vitamin A levels over time,” she adds.
Daily vitamin A requirements range between 1,000 and 1,800 international units (IU) per pound of forage dry matter for growing cattle and lactating cows, respectively. Vegetative grass contains approximately 18,000 IU of vitamin A per pound of dry matter, whereas alfalfa hay contains about 1,300 IU. With that said, beta carotene is subject to degradation, and even properly stored hay can lose up to 50% of total beta carotene concentrations after one year.
Grain and other ingredients contribute little beta carotene to livestock diets. For example, dried distillers’ grains have about 200 IU of vitamin A per pound of dry matter and cracked corn contains roughly 70 IU. Luckily, Briggs says adding vitamin A to winter feeding programs is both simple and affordable.
Mixes and injections
Provide cattle with mineral mixes formulated specifically for winter feeding. Vitamin A will degrade with exposure to heat, light, moisture, and trace minerals, so plan on buying smaller quantities of your mineral mix in shorter intervals instead of stocking up on a large supply that degrades.
Give vitamin A injections to pregnant cows at least two months precalving to boost nutrient stores and ensure vitamin A is available in colostrum. With that said, a single injection won’t be enough for cows showing obvious signs of deficiency.
“These cows have a diminished capacity to store vitamin A in their livers, which means they might require more injections until their vitamin A reserves are sufficient or until adequate oral supplementation can be established,” Briggs says. Moreover, calves have minimal vitamin reserves and will depend on supply from their mothers’ colostrum and milk, so it will be critical to maintain vitamin A levels throughout early lactation.
