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Do your cattle get enough vitamin D?

Corwin Nelson Published on 24 September 2015
Cattle in feedlot

For most beef producers in North America, the answer to the title of this article depends on the season. Vitamin D is not always an essential nutrient for cattle, as vitamin D3 (the main form of vitamin D utilized by cattle) is produced in their skin when exposed to the sun’s UVB rays – hence its nickname as the sunshine vitamin.

The intensity of the summer sun, consequently, results in adequate vitamin D3 production in cattle, but that is not the case for the winter sun in most of North America.

Vitamin D plays a critical role in bone formation and regulating calcium and phosphorus balance in cattle. We also have recently learned that vitamin D helps to activate important immune defenses of cattle.

While dairy cattle usually receive plentiful amounts of supplemental vitamin D (30,000 – 50,000 international units of vitamin D3 daily) in recognition of the calcium demands of milk production, little attention has been paid to the vitamin D status of beef cattle because it is often assumed they get what they need from the sun.

With the realization that vitamin D also plays a role in immunity, however, there has been more attention given to the vitamin D needs of beef cattle.

Contrary to commonly held assumptions, beef cattle are often not getting enough vitamin D during the late fall to spring months. Scientists at the USDA National Animal Disease Center reported a study that indicates vitamin D supplies of feedlot cattle plunge drastically over the winter.

The study took place in Nebraska and represented a common beef production cycle in which calves were born in the spring, grazed on pasture through the summer, weaned in the fall and placed in a feedlot where they were fed a typical feedlot ration that provided 800 to 1,200 international units of vitamin D3 per head per day.

The serum 25-hydroxyvitamin D concentrations of those calves on average were 26 ng per mL in early summer, roughly 45 to 50 ng per mL in late summer and 55 to 65 ng per mL in late fall. The following March, after they had been in a feedlot for the winter, their 25-hydroxyvitamin D dropped to roughly 15 ng per mL of serum.

Concentrations below 20 ng per mL are generally considered deficient for cattle. I would argue that concentrations below 30 ng per mL are less than ideal. Based on what cattle normally acquire from summer sun exposure, concentrations of 40 to 80 ng per mL are a good target.

The values of 25-hydroxyvitamin D concentrations in serum are not meaningful from a practical beef management perspective, but they are useful for veterinary diagnostics. I provide them here as a means of giving a benchmark for the recommendations I will give later in this article. I also want to point out that the supplemental vitamin D3 provided in the feedlot ration mentioned above (800-1,200 international units per head per day) was woefully inadequate.

The vitamin D status of newborn beef calves also is bleak, according to a study presented at the national meeting of animal scientists this past July. The study included 59 calves from herds in Florida (Angus and Brangus), Idaho (Charolais) and Minnesota (Angus).

The 25-hydroxyvitamin D concentrations at birth in the spring were approximately 15 ng per mL of serum on average for calves in both Florida and Minnesota, and below 10 ng per mL for all of the calves sampled from the Idaho herd. In total, most calves were below the 20 ng per mL mark. Their 25-hydroxyvitamin D concentrations increased over time, though, and were near 45 ng per mL by mid-summer and 60 ng per mL by the end of summer.

All of this indicates the current vitamin D status of many newborn beef calves and feedlot cattle is well below what is normally considered adequate for cattle. More often than not, the consequences of low vitamin D supplies go unnoticed because cattle appear healthy. The real problem, however, is that inadequate vitamin D puts them at a greater risk for impaired bone formation and immunity.

Those risks are amplified under stressful conditions beef calves will experience. Luckily, there are some easy and inexpensive solutions that can be implemented to improve the vitamin D status of beef calves and feedlot cattle.

The good news for beef producers is that vitamin D3 is inexpensive, requiring just pennies per year to meet the vitamin D needs of one animal. The solution for feedlot cattle is to increase the concentration of supplemental vitamin D3 in the ration or vitamin/mineral supplement.

Talk to your nutritionist or feed supplier to get the supplemental vitamin D3 increased to provide a daily intake of 10,000 to 20,000 international units per head, or about 25 international units per pound of bodyweight. That rate is on par with the typical supplemental rate for dairy heifers and achieves the 40 to 80 ng per mL target range for 25-hydroxyvitamin D.

I do not recommend exceeding 25 international units per pound of bodyweight, as there is currently no evidence indicating that more is better. Feedlot cattle do not need that much vitamin D over the summer if they are outdoors, but to keep matters simple, there is no harm in supplementing at the same rate year-round.

For newborn beef calves, I recommend an injectable source of vitamin D3 at birth to build the vitamin D stores. Even though the springtime sun will stimulate vitamin D production in their skin, it takes a couple of months to reach adequacy.

Based on experiments I have done, 200,000 international units of vitamin D3 injected at birth will boost serum 25-hydroxyvitamin D of calves to near 50 ng per mL. Newly received feedlot cattle also may require an injection of vitamin D3, particularly those arriving in the winter and spring months, and you should consider the background of those animals in making that decision.

Injectable vitamin D3 products are often found in combination with vitamins A and E. Vitamin A and E deficiencies also can occur in calves born from cows eating winter forages; so the combination of vitamins A, D and E in an injectable product is a good option.

To achieve the 200,000 international unit dose of vitamin D3, I recommend products that contain at least 50,000 international units of vitamin D3 per mL of product. However, not all injectable products are equally effective, so ask the supplier of the product to provide verification that their injectable product will work.

The vitamin D needs of brood cows are not as much of a concern as calves and feedlot cattle. In the newborn calf study mentioned above, the dams of those calves had 25-hydroxyvitamin D concentrations above 40 ng per mL of serum at the time of calving.

However, even though the cows had enough vitamin D for their own needs at the time of calving, they may not have had surplus vitamin D stores to pass on to their calves.

The mineral supplement given to those cows provided them around 3,000 international units of daily supplemental vitamin D3. In comparison, dairy cattle, as mentioned above, typically receive 30,000 to 50,000 international units of supplemental vitamin D3 daily and, in my observations, vitamin D status of newborn dairy calves is somewhat better than that of beef calves.

Therefore, greater inclusion of vitamin D3 in winter vitamin/mineral supplements for brood cows may improve the vitamin D status of their calves.  end mark

PHOTO: Cattle begin to require more Vitamin D from late fall to the spring months, as exposure to the sun starts fading. Staff photo.

  • Corwin D. Nelson

  • Assistant Professor of Physiology
  • Department of Animal Sciences University of Florida – Gainsville
  • Email Corwin D. Nelson

More about vitamin D

  • Cattle can utilize two forms of vitamin D: vitamin D2 and vitamin D3. Vitamin D3 is the form naturally produced in the skin and the recommended supplemental form. Vitamin D2 is produced from ergosterol in fungus. Cattle can acquire vitamin D2 from forages, but it is not as effective as vitamin D3.
  • Vitamin D is often measured in international units. One milligram of vitamin D = 40,000 international units.
  • The best indicator of an animal’s vitamin D status is the serum concentration of 25-hydroxyvitamin D. The target range for 25-hydroxyvitamin D is 40 to 80 nanograms per milliliter (ng per mL) of serum.

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