Vitamin D: Optimizing Levels for Cattle Health and Performance

Vitamin D plays an essential role in animal health. Commonly known as the “sunshine vitamin,” vitamin D3 can be produced in the skin when exposed to UVB light from the sun. However, the rate of production of D3 via sun exposure varies between species, skin color, geographical region, and time of year. It is important to understand the vitamin D needs of beef cattle, as well as its specific forms and functions, because sunshine alone may not provide enough D3 for optimal health and performance.

Vitamin D is essential for developing robust bones in animals. It regulates the absorption of calcium (Ca) and phosphorus (P), both of which play a crucial role in bone calcification. It also has been shown to activate a critical innate immune defense in cattle against microbial pathogens and can influence the expression of genes related to muscular anabolism and protein synthesis in feedlot cattle.

Three ways to get vitamin D
Animals can get vitamin D in three ways: produced in the skin with exposure of UVB light from the sun; supplemented in the diet as D2 (ergocalciferol) or D3 (cholecalciferol); or supplemented in the diet as the bioactive metabolite 25-hydroxyvitamin D3 (25-OH D3), which is the circulating form of vitamin D in the body.

When vitamin D2 or D3 is included in diets, it must go through two metabolic transformations in the body — first in the liver and then in the kidneys — before it reaches a form that is bioavailable. This time-consuming process reduces the effective level of vitamin D3 in the bloodstream. When 25-OH D3 is provided, the conversion step in the liver is bypassed allowing a faster and more efficient uptake of the required metabolite, increasing serum vitamin D levels and contributing to stronger bones and healthier, more productive animals.

Determining optimal vitamin D levels to support its multiple functions in the body is the focus of actively ongoing research in ruminant nutrition. Studies have shown that levels <5-7 ng/mL serum 25-OH D3 will result in rickets or clinical signs of deficiency. Furthermore, levels between 10-20 ng/mL have been reported as insufficient for Ca and P homeostasis, jeopardizing bone health. Adequate supply for immunity has been identified theoretically as >30 ng/mL serum 25-OH D3, while serum levels >100 ng/mL have been associated with increased performance (Nelson et al., 2016).

Sunshine alone is not enough
Casas et al. (2015) evaluated seasonal effects on vitamin D status in calves through feedlot animals in the central region of the U.S. Serum 25-OH D3 concentrations of calves soon after birth and feedlot animals during winter months were considered insufficient (26.3 ng/mL and 15.2 ng/mL, respectively) even when supplemented NRC levels of vitamin D3. In addition, Nelson et al. (2016) evaluated vitamin D status in beef cows on pasture in multiple regions of the U.S. The majority of cows had serum 25-OH D3 levels around 60 ng/mL and were considered suboptimal — even in summer months and following supplementation with NRC levels of vitamin D3. In both studies, supplemental vitamin D3 and sun exposure was not enough to elevate serum 25-OH D3 concentrations to levels needed to see optimal health and performance responses.

Although too often taken for granted as a secondary nutrient, vitamin D is an essential vitamin that plays a significant role in the growth, production and health of beef cattle. The key to meeting vitamin D needs is to target levels according to production stage, season and geographical region, as well as by providing the nutrient in a bioavailable form that ensures serum 25-OH D3 concentrations reach optimum levels efficiently. Don’t let fluctuations in levels and form of “the sunshine vitamin” undermine cattle performance and profitability.

Meet the growing needs of your herd year-round with Hy-D®

Benefits of feeding Hy-D®:

• Increased 25-OH D3 status
• Improved immune function
• Optimizes calcium and phosphorus retention
• Provides prenatal support to developing calf

Use recommendations to optimize vitamin D in your cow/calf operation:

• If already supplementing vitamin D3:
•           5,000 IU equivalent of D3 + 5,000 IU equivalent of Hy-D®

• If not feeding any vitamin D3:
•         10,000 IU equivalent of Hy-D®