Vitamin A important for cow herds 

If a beef producer knows what they’re looking for, baby calves will show them the tell-tale signs of vitamin A deficiency. Diagnosing cows can get a little trickier. 

Kathy Whitman, a Colorado State University veterinary Extension specialist, told attendees in a recent webinar how important vitamin A is in cattle diets, especially before the green grass arrives.  

“Vitamin A is a critical nutrient, and I don’t want to make it sound like it’s the only important nutrient, but certainly, if you manage vitamin A, it’s one of them that’s pretty unstable in our harvested forages,” she said. “If we manage that, then we’ll probably get a lot of other things correct.” 

Supplementation of vitamin A year-round is not necessary, especially if cows have forage in the spring and summer months. 

“Once they get on those fresh, green, growing forages, they’re going to have plenty of vitamin A to consume and plenty of vitamin A to store,” Whitman said. 

Supplementation of vitamin A can then start about three months after cattle finish their last bite of green forage, she said. Plus, producers can save money by not having lick tubs out year-round or needlessly supplementing vitamin A. 

“These supplements that you put out in the wintertime to try to combat some of these issues are only good as your four balancers—your protein, energy, calcium, and phosphorus—and so you need to balance for those things first,” she said. “Otherwise, your supplement program isn’t going to be effective.” 

If the cows are deficient in protein or total digestible nutrients, they’re simply not going to perform as well regardless of how high a quality supplement is added, and that is why she is a believer in testing feed quality. 

Healthy cows key

Whitman said to keep the cows healthy otherwise it keeps other problems at bay. Cows in the third trimester around the time the grass has yet to green up are at a critical juncture and producers need to make sure the cows get enough vitamin A. 

“Obviously this is a time of significant calf growth, and then also her colostrum formation,” she said. “One thing that I want to emphasize is that there’s minimal transfer of vitamin A across that placenta when that calf is in her uterus and so make sure that cow is sufficient in vitamin A.” 

Whitman said a cow needs to be able to deposit vitamin A into her colostrum. For a pregnant cow, she needs about 1,300 international units of vitamin A per pound of feed intake. Lactating cow rates are a little bit higher.  

“When they don’t have green forage available, it’s about 30,000 to 100,000 international units a day,” she said, acknowledging that is a wide range for ranchers to consider. 

Whitman did a quick calculation for a 1,500-pound cow, with 2.5% of her body weight intake. That is about 35.5 pounds of feed a day, making her requirement just under 49,000 international units a day if she’s pregnant or 67,500 units if she’s lactating. Cattle typically have two to four months of liver storage of vitamin A, she said. 

“So, when they’re on these green, growing forages in the summertime and in the fall, they can get some of that liver stored up, and they can last some period of time,” she said. “When we have restrictions on that green forage, then then our storage is less and so our supplementation requirements are even more critical.” 

A pound of dry matter of fresh forage has more than 18,000 international units per pound, so a mature cow will easily achieve her requirements for vitamin A and then some. 

“This gives her the opportunity to store some of that excess vitamin A that she’s consuming,” she said.  

Drought considerations

Forage quality of pastures and rangelands or whatever the cows are grazing during the spring, summer and fall—any time these are impacted by drought—it’s going to shorten the season.  

“That’s going to blunt the growth of those forages, and that cow’s ability to store some of that vitamin A is going to be limited this season,” she said. “So, as we get further into the season, our vitamin A levels are going to be decreasing, so certainly we can have that sort of issue going on in these cows.” 

When it comes to feeding hay, the age and quality of hay are critical factors. 

“As hay gets older, it’s going to lose the vitamin A content as well as other fat-soluble vitamins like vitamin E and D,” Whitman said. “Now when we talk about harvesting hay and the TDN and protein that we get when we feed that hay, those things really aren’t going to change. But if we’re talking about harvesting hay in July that we’re going to feed in February, we lose a significant amount of that vitamin A content, and those fat-soluble vitamins.” 

When looking at feed analysis of hay, the age of it needs to be considered when it’s fed. If there happens to be nutrient chelators within those harvested forages, things like high nitrates, those tend to bind with some vitamins.  

“If we’re not feeding a high-quality hay to these cows during the third trimester and into lactation, then they’re simply not going to be able to consume enough feed to not only supply their protein and energy requirements, but also you’re going to be missing out on even more vitamin A,” she said.  

Veterinarians, Whitman said, when they’re dealing with deficiencies in the cows, the first place they’re going to see it is in the calves.  

“Calves that are born to vitamin A deficient cows can certainly be born weak, or they can die shortly after birth,” she said. “They can have some eye issues, some small eyeballs or cataracts, and those would be pretty significant issues.” 

If it is the cow that’s deficient it can negatively impact the calf when it’s born and certainly impact the colostrum quality, she added. 

Not getting enough vitamin A into that colostrum spells trouble because that’s the first source for that calf when it’s born, she said. “It can lead to some health issues along the way, diarrhea being one of those, probably due to some immune dysfunction, and they continued for poor performance of that calf.” 

It becomes even more critical if the calf has a failure of passive transfer from inadequate colostrum.  

“Again, if a calf has a failure of passive transfer, you need to consider that they may have a vitamin A deficiency, simply because that’s really their primary source when they’re first born,” she said. 

Cows tend to have more clinical issues that are obvious to the naked eye. Poor hair coat is one example of a deficiency. 

“You may have some abortions or retained membranes, and this is going to be in a group of cows, not on an individual animal basis,” she said. “So, keep that in mind, if you’re dealing with a vitamin A deficiency in your herd, you’re going to have more retained placenta than what you would routinely expect. We don’t see that a lot of beef cattle, and so if you’re seeing several of those, you might want to consider vitamin A in your list of potential causes.” 

Some subclinical signs that aren’t obvious could include poor reproductive performance and decreased immune function.  

“If we’re struggling to figure out why we’re having some of these issues, why these cows aren’t breeding back, why we’re having some more disease than we would normally expect, despite the fact that we have a good vaccination program, we may want to have some nutritional considerations and include vitamin A on that list,” Whitman said.  

Kylene Scott can be reached at 620-227-1804 or [email protected].