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In brief:
Milk is a good source of calcium (Ca), but that Ca must come from somewhere. Cows have been bred for higher milk yields, but their ability to absorb Ca has not changed.
An appropriate calcium level in blood is essential for the well functioning of the immune system, and its adequate homeostasis is essential for a succesful transition period. However during an important part of the beggining of lactation, cows experience a negative calcium balance.
A typical 500 kg dairy cow normally contains 6 kg of Ca (SCA, 1990). In the first 9 weeks of lactation, a cow may be in Ca deficit by up to 10 g/day (Kronfeld, 1976). If this deficit is not corrected, up to 10% of the stored Ca may be used to maintain milk production. With each new lactation, the animal may be starting with a lower Ca store, increasing the risk of hypocalcemia (Figure 1). It is therefore vital to help the cow recover from this Ca deficit by promoting Ca absorption throughout the production cycle. During early lactation to recover from the natural negative calcium balance as quick as possible and throughout the whole lactation to replenish the mineral reserves in the bones.
Figure 1. Calcium levels in a high-performing dairy cow over time. Ca reserves may not be replenished, increasing the risk of hypocalcemia in older animals (Source: McGrath et al., 2015)
Figure 2 shows how vitamin D plays a key role in Ca/P metabolism (green boxes) and immunity (purple boxes).
Figure 3 illustrates the optimal blood serum levels of vitamin D in dairy cows. Most cows have insufficient vitamin D levels, but Nelson et al. (2016) showed that optimum immunity support is achieved when serum levels exceed 100 ng/ml. Current supplementation strategies may not be sufficient to reach these optimal levels. Serum levels of 40 – 80 ng/ml were considered adequate until 2014 for basic Ca and P homeostasis and immune function. However, research development from 2018 onwards has elucidated massive advantages at levels above 100 ng/ml, resulting in better Ca metabolism, immunity and milk production.
At levels around 5 ng/ml, clinical symptoms of vitamin D deficiency start to appear, such as rickets or osteomalacia.
Figure 3. Optimal blood serum levels of 25OHD3 in dairy cows
The two common ways of absorbing vitamin D are via the sun, or through feed, commonly as vitamin D3. However, there is a major limitation as to how much a cow can transform into 25-OH vitamin D3, which is later converted in the kidney into 1,25OHD3, the active form (Figure 4). There are many different sources of vitamin D available on the market. Hy-D® is an immediate source of vitamin D.
Figure 4. Illustration of vitamin D metabolites and how Hy-D® delivers an immediate source of vita
The key advantage of Hy-D® as a vitamin D source is that it ensures the animal can reach blood levels associated with optimal immune function, which through common vitamin D3 cannot be attained. (Nelson et al., 2010).
Poindexter et al. (2020) showed that supplementing dairy cows with vitamin D3 at 1 or 3g gave statistically (p<0.05) the same result in 25OHD3 blood concentration, making clear that the liver’s bottleneck won’t allow to reach the ideal levels through this source. However, 1 mg of Hy-D® resulted in 1.5 times the amount of 25(OH)D3 in the blood plasma on day 7, and 2.7 times the amount on day 28 compared to a standard vitamin D3 supplement (Figure 5). In just 14 days of supplementation of Hy-D® at 1g, on top of 20 000 IU D3 supplementation, the blood levels were at optimal levels.
Figure 5. Serum concentration of 25(OH)D3 in dairy cows over time when supplemented with a standard vitamin D3 or Hy-D® (all treatments were provided on top of a basal level of 20 000 IU vitamin D3).
McGrath et al. (2012) analyzed plasma concentrations of Ca and P over time in steers fed a diet containing Hy-D® or a standard vitamin D3 supplement (the control group) as a way to test Hy-D®’s capacity to increase absorption of Ca and P. As shown in Figure 6, Hy-D® increased the plasma levels of Ca and P after 10 days of supplementation. Additionally, this resulted on a significantly higher Ca and P retention in the body at the end of the measurement period, meaning an improved Ca and P homeostasis (Table 1).
Figure 6. Comparison of mean plasma calcium (Ca) and phosphorus (P) levels in steers supplemented with a standard vitamin D3 (the control) or Hy-D®
Table 1. Mean mineral balance of calcium and phosphorus in steers supplemented with or without Hy-D®
These results show how vitamin D supports Ca and P metabolism, ultimately promoting bone mineralization which improves the health status of the animal.
As mentioned earlier, vitamin D plays a role in the activation of gene expression for genes active in immunity. In 2021, Vieira-Neto et al. confirmed that supplementing dairy cow diets with Hy-D® better prepares the animal for immune activity by ‘waking up’ the dormant genes and stimulating gene expression. The heat maps in Figure 7 show more activity (activated genes on green) in the genes of animals fed a diet supplemented with Hy-D® compared to animals fed a standard vitamin D3 supplement (inactivated genes on red color).
Figure 7. Effect of different vitamin D source on peripheral blood leukocyte gene expression (p < 0.05). Prepartum samples (A) were taken after 20 days of supplementation (-30 to -10 days in milk) and the postpartum samples (B) were taken 13 days later (3 days in milk)
Having better immune related gene expression, should result on better immune response to infections. Poindexter et al. (2020) tested the immune reaction to a mastitis challenge in mid-lactation cows by infecting the mammary gland with S. uberis and compared the reaction of animals supplemented with standard vitamin D3 or Hy-D® (Figure 8). Cows supplemented Hy-D® had lower clinical outcome of infection, required less use of antibiotics, had a lower infection severity and had lower rectal temperatures than cows with conventional D3 (differences were numerical, severity showed significance, p<0.05).
Figure 8. Effects of vitamin D source (D3 or Hy-D®) and DCAD strategy (negative or positive) on indicators of mastitis severity during a challenge with S. uberis
The improved immune status promoted by Hy-D® supplementation in the cow is also passed on to the calves via the colostrum. In another trial by Martinez et al. (2018) colostrum yield and quality was enhanced when supplementing Hy-D® during close-up period for cows at both negative and positive DCAD regimes. The results are shown in Table 2. These results show not only that the calf will have a better immunity through a colostrum significantly richer in IgG (p<0.05), but also that the immunity of the cows is much stronger at that point.
Table 2. Effect of dietary cation-anion difference (DCAD) and vitamin D source in pre- and post-partum diets
Addressing the calcium deficit and immunity issues in cows are of great relevance to promote animal health, longevity and productivity (link to earlier article). In this article we spoke about how raising vitamin D levels to optimal levels can be a great enhancer to promote better Ca metabolism and also cow and calf immunity, however reaching optimal levels of vitamin D with convential vitamin D3 sources has been proven impossible, even if providing doses three times higher than what’s common.
Hy-D® comes in, as the best tool to uplift vitamin d levels in blood to optimal levels and supporting Ca metabolism and immune capacity, overall resulting on better health status, lower incidence of diseases and eventually longer and better living cows.
30 September 2024
Ignacio holds a bachelor's in Agriculture Sciences and a master's in Sustainable Animal Nutrition and Feeding. He is the Global Marketing Manager for Ruminants at dsm-firmenich, and has supported farmers, nutritionists, and health experts on promoting productive performance through health protection and efficient use of resources.
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