Feeding excessive vitamins detrimental to dairy cows

COLUMBUS, Ohio — Vitamins are essential for dairy cows, but feeding too much can cause problems.

“If you feed the right amount of vitamins, we expect better cow health, improved reproduction, it can increase milk yield, improve the nutritional value of milk and dairy products and be a profitable addition to diets,” said Bill Weiss, professor emeritus at The Ohio State University.

“But too much is detrimental to health, it can reduce milk yields, it inflates feed costs and that can reduce profitability,” said Weiss during a webinar hosted by Hoard’s Dairyman.

“Vitamins are involved as enzyme cofactors in metabolism of almost every nutrient so just about anything a cow does needs a vitamin,” the university professor said.

“We think a cow needs to absorb 12 vitamins including the fat soluable vitamins A, D, E and K,” he said. “Vitamin K is largely ignored because rumen bacteria make vitamin K so it’s a nonissue for dairy cows.”

The water soluble vitamins include biotin, B-12, folic acid, niacin, pantothenic acid, riboflavin and thiamin.

“We don’t supplement most of these,” Weiss said.

“Because of limited data for vitamins, the accuracy of how much a cow exactly needs isn’t known with high precision,” he said. “So, we picked the minimum value shown to have an effect and we consider that adequate intake like a requirement.”

The potential responses from vitamin A are reduced retained placentas, abortions and mastitis, as well as increased milk production.

“Some of the increase in milk is because of health and some is metabolic,” Weiss said. “Too much vitamin A can reduce vitamin E absorption, reduce milk production and cause toxicity.”

The adequate intake for vitamin A is 50 units per pound of bodyweight or 75,000 to 80,000 units.

“For cows producing more than 75 pounds of milk, for every pound over 75, add 454 units to cover the vitamin A that is secreted in the milk,” Weiss said. “The amount for pre-fresh cows is the same as dry cows because there is no data that shows feeding increased vitamin A did any good.”

Vitamin A can break down during storage.

“If vitamin A is stored in a premix, in cool conditions and away from sunlight, you lose about 3% per month,” Weiss said.

“If you put vitamin A in a trace mineral premix, you can lose up to 9% per month if the premix contains inorganic trace minerals,” he said. “So, if it’s not stored correctly or for too long, you’re going to have to increase supplementation rates.”

When cows were fed 500,000 units of vitamin A per day or 6.5 times the adequate intake during the dry period, Weiss said, milk yield was significantly lower.

“At 800,000 units or 12 times the adequate intake, the cows developed osteoporosis,” he said. “So, you clearly want to avoid those excessive amounts.”

Vitamin D is made by cows from sun exposure.

“The adequate intake for vitamin D for dry cows is 25,000 units per day and for lactating cows it’s 30,000 units based on limited sun exposure for confinement cattle,” Weiss said.

An experiment in Denmark looked at how much vitamin D a cow can make when exposed to the sun.

The researchers evaluated four levels of sun exposure — no skin covering, only covering the udder of the cow, covering almost everything but the udder, legs and head and covering everything but the head and legs.

The cows started the study with vitamin D deficiency and they were turned out to pasture.

“Within three weeks, the cows with no cover were adequate for vitamin D and the ones with only the udder covered took a little longer,” the university professor said. “The cows with everything covered never recovered and remained vitamin D deficient.”

Cows outside in direct sunlight during the summer need five to six hours to make enough vitamin D to meet their needs, Weiss said.

“During the fall, winter and spring, the sun is not direct enough to get good synthesis rates,” he said.

For vitamin E, the adequate intake is 1,000 units per day for dry cows, 500 units per day for lactating cows and 2,000 units per day for pre-fresh cows, Weiss said.

“Cows transfer almost no vitamin E to the fetus,” he said. “That’s one more reason why colostrum is so important because that’s where calves get vitamin A and E.”

For a typical cow close to calving, the amount of vitamin E in the plasma decreases significantly, Weiss said.

“If we feed excess vitamin E during the prefresh period that almost eliminates the drop,” he said. “That’s why we recommend higher levels of vitamin E at prefresh.”

Many of the water soluble vitamins are B vitamins.

“Rumen bacteria make B vitamins, so if you supplement a lot of B vitamins, they’re destroyed,” Weiss said. “There has never been a clinical deficiency of B vitamins ever shown in a healthy cow.”

Supplementing some B vitamins can have positive effects.

“Biotin improves hoof health and it’s been shown to increase milk production by about three pounds,” Weiss said.

“Feeding niacin at 12 grams per day has been shown to increase milk production, but there’s a lot of variability,” he said. “It might reduce ketosis and body temperature, but it takes a lot of niacin because so much is degraded.”

Dairymen should not expect a lot of response from B-12, although fresh cows may benefit.

“In a study with B-12 plus folic acid that was given by injection, the result was increased milk,” Weiss said. “But the economics are probably not there.”

When feeding choline at 12 grams active, it must be rumen protected.

“Almost 100% will be destroyed in the rumen if it is not protected,” Weiss said.

The results from adding choline to the ration have been positive.

“It increases colostrum if you start supplementing in the pre-fresh period and it increases milk production in early lactation, four to five pounds a day,” Weiss said.