Cows May Need Vitamin A Supplementation after Drought
Vitamin A is crucial to health; it is important to the immune system and healthy epithelial tissues (skin, digestive tract lining, etc.—covering all the internal and external surfaces of the body).
Bera-carotene, the precursor to Vitamin A, is plentiful in green forages, so cattle are never short of Vitamin A if they are on green pasture during summer. The question many ranchers have this winter, after severe drought in much of the West and Midwest last summer, is if cows might be short on this important nutrient.
If a herd is short of vitamin A through winter, probably the first thing you’d see in the calving cows is poor quality colostrum, before you’d actually see any signs of vitamin A deficiency in the animals, according to Dr. Dave Barz, (veterinarian at Northwest Veterinary and Supply, Parkston, South Dakota. Good colostrum is important for the calf, and if the cow is low in vitamin A this will impair the calf’s ability to gain passive transfer of antibodies and have the necessary immunity.
It’s hard to truly diagnose a vitamin A deficiency because there are generally multiple factors involved. “We might see general unthriftiness, rough hair coat, etc. There will be signs but nothing so definitive that you could say for sure that this is a vitamin A deficiency. It would have to be quite extreme,” says Barz.
Mary Drewnoski, Nebraska Extension Beef Systems Specialist, says she had a lot of questions from producers about vitamin A two years ago. “So we did an extensive look into the literature. I learned that abortion is not the main issue we’ll see; it is calf health. Cows can be quite deficient and have a live calf but the calves will have poor immunity, and diarrhea is common.”
After a drought, vitamin A stores in the body may be low. “Fresh green grass is very high in beta-carotene, and the amount of vitamin A stored in the liver can help see cows through winter, if they had green grass in summer,” she says.
“Typical recommendations assume the cows are spending 4 months on green grass, and can use stores from the liver. The recommended supplement, plus stores, will be adequate for cows while eating harvested, stored forage. In drought, however, there may only be a short period with green grass. Cows may not have enough time to store enough vitamin A,” she explains.
Spring–calving cows may end up short of vitamin A during their third trimester. They may have depleted their stores by the time they calve. “This is where we can run into problems,” she says.
“Late gestation is the most important time. A cow must provide all the vitamin A the calf needs, via colostrum. If she doesn’t have it to give, the calf will be shortchanged. Calves are born deficient but colostrum supplies what’s needed—if the colostrum is adequate. This is very important for the calf’s immune response.”
If the calf is short on vitamin A, multiple systems are affected. A common sign of vitamin A deficiency in calves is diarrhea. You might think the calf got a load of E. coli or some other pathogen to cause the diarrhea, but the root cause is vitamin A deficiency.
The immune system is weak, which allows more chance for infection, and the gut lining may be compromised because of the deficiency.
“After drought, or any prolonged period of not having green, fresh, forage, we need to think about increasing the supplementation. The typical suggestion is to provide about 42,000 IU daily for a dry cow, and 59,000 for a lactating cow, but those numbers assume that the cow still has some stored vitamin A in her liver.”
“Based on what we see in confinement systems, and literature from Australia, the suggestion is to bump that up to 100,000 IU if there’s a long period of drought, or when cows are not consuming much green, fresh forage. The main focus would be on the late-gestation cow,” says Drewnoski.
Older cows are more likely to have larger stores of vitamin A because they’ve spent more of their life on green grass. “During some periods they are able to build up more stores than they use, especially if you’ve provided a supplementation program. The 2 and 3-year-old cows tend to have more problems. The older they get, the more likely they’ll have higher stores. It’s the young cows that need more supplementation. I’m not saying you don’t need to feed it to older cows, but if it comes to a choice I would focus on the younger cows,” she says.
They also have the least ability to provide adequate antibodies in colostrum. First-calf heifers generally don’t have as much quantity and quality of colostrum as older cows. “This can be a double whammy for their calves; sometimes poor immune response in the calves may be due to several factors.”
Harvested hay doesn’t have as much beta-carotene as fresh green grass, but if it was put up in good condition–immature and green and not too dry, and still has all its leaves–it will have better levels than overly-mature hay. The high level of beta-carotene drops over time, but even year-old or 2-year-old hay that was put up well and protected from moisture and oxidation will be better than dry, overly mature hay. “Color is a great indicator. If it’s 2 years old and still really green, it probably is still a decent source of beta-carotene,” she says.
“Green pasture has 10 times the concentration of good, green alfalfa hay. Green stored forage is, however, a better source than brown forage, but still not as good as green grass. Green stored forage will probably provide about a third of the cows’ requirement, if it’s their full diet. Thus you still want to supplement.”
Some people wonder about using injectable vitamin A, versus a feed supplement. “It’s a good way to get a short-term boost, but if you look at the cost of an injectable product and the amount it provides, versus what the cow would get with a supplement provided in feed, it’s no contest. It’s better to have it daily in a feed source. An injectable won’t provide long-term sustained improvement and is quite expensive per unit of vitamin A,” she says.
“This doesn’t mean that in a situation where you are concerned about vitamin A levels you should not give a calf an injection at birth. It can help, but it’s better to make sure we don’t get into that situation.” It’s better to be proactive and supplement the cow adequately before she calves.
Barz rarely recommends injectable vitamin A anymore. “I am 73 years old, and 50 years ago nearly every cow-producer in our area gave cows an A&D shot at preg check time or before calving. The injectable vitamin A gives a quick supply but is not long-lasting. We also saw quite a few reactions to the injections. Ranchers generally gave these injections to all their cows but then we quit doing that, and started giving it to the calves—but now we don’t even use injectable vitamin A in calves very often. We rely more on a good feed supplement, and these have improved in the past 50 years,” he explains. “In our area cows are getting grain-based cubes that are heavily supplemented with vitamins.”
MINERALS ARE ALSO IMPORTANT – Barz says that his area was very dry in 2021, but most producers had adequate feed. “This isn’t a range area; it’s farmers with cows. They are feeding a lot of supplement. Calving was getting started in early February for purebred folks, but most other producers are now calving later, to have better control of scours. What we’re seeing at this point in time (February) in some of our OB cases is heifers and cows that are not dilating properly and therefore slow to calve,” he says.
“This problem is a function of inadequate vitamins, minerals, etc. We recommend that cows be supplemented and have adequate nutrition before calving. We’ve had good success using Multimin (injectable trace minerals); many producers use that in their cows, and in feedlot animals—especially calves coming in from severely drought-stressed areas,” says Barz.
“You can feed these minerals to cattle but it will take 30 days for their mineral levels to improve, whereas with the injection those levels come up immediately. Many purebred breeders are using Multimin and a lot of folks also give a small dose at birth to young calves.” This ensures that the important trace minerals—crucial to a healthy immune system—are adequate during those first weeks of life when calves are so vulnerable to various diseases.
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