Do our pigs get enough vitamin D3?

In Brief:

• Vitamins play a crucial role in human and animal nutrition. One goal of animal nutrition is to ensure an optimal supply of vitamins. This is not just a matter of avoiding deficiency, but of ensuring enough vitamins for healthy and sustainable production with high animal performance!
• In this context, the importance of an optimal supply of vitamin D is becoming increasingly important in pig production.

D3 synthesis in the skin can only take place under lN-B radiation in the range of approx. 290-315 nm (Holick et al. 2007). In modern housing systems, however, pigs usually have little or no access to direct sunlight. This means that the skin is largely unable to produce D3. Accordingly, the animals' feed is enriched with vitamin D supplements. In the EU, the maximum limit under feed legislation for pigs is 2,000 IU of vitamin D3 or an equivalent amount of 50 µg of the vitamin D3 metabolite 25-hydroxyvitamin D3 (25-OH-D3), which is derived from Saccharomyces cerevisiae and is authorised by the EFSA as an alternative source of vitamin D. This maximum limit applies regardless of whether vitamin D3 or 25-OH-D3 (Hy-D®) is used. Where both sources of vitamin D are combined, the sum must not exceed the maximum total amount of 2 000 IU (conversion: 1 µg = 40 IU) (IMPLEMENTING REGULATION (EU) 2024/1070). The same maximum value for vitamin D3 in pig feed was already specified over 50 years ago in the Official Journal of the EEC (European Economic Community) of November 23, 1970 (70/524/EEC). At that time, feed conversion ratio (FCR) in pig fattening was still 3:1, and the meat:fat ratio was 1:0.79. (Steffen et al. 1970). Today, we have an FCR of 2.44:1 (LWK Lower Saxony) and a meat:fat ratio of 1:0.37 (Federal Agency for Agriculture and Food). By the time it reaches 110 kg, a pig today has consumed at least 50 kg less feed than it did 56 years ago. Consequently, it absorbs fewer vitamins, including vitamin D3. At the same time, its body fat percentage is lower, meaning there is less fat available to store vitamin D.

Vitamin D3 metabolism and its role in immunity and performance

When formulating pig feed, the legal framework is often already being pushed to its limits due to the increased performance levels. In addition, numerous studies over the last ten years show that the influence of vitamin D3 goes far beyond pure calcium homeostasis. For example, vitamins play a fundamental role in modulating innate and adaptive immunity and can have a positive effect on muscle growth (Hasan et al. 2023). The positive effects of vitamin D3 on physiological functions depend crucially on the concentration of 25-OH-D3 in the blood. This vitamin D3 metabolite is physiologically formed in the liver from D3; it is the predominant circulating form and the storage form of vitamin D3 in the body. Due to its good correlation with vitamin D3 intake and its long half-life (10 – 21 days; Flohr et al., 2014), 25-OH-D3 is generally used as a measure of vitamin D status (Lütke-Dörhoff et al. 2022). When needed, 25-OH-D3 is converted into the hormone 1,25-(OH) 2-D3, primarily in the kidneys but also in other tissues. This hormone is metabolically active and is closely controlled and regulated via a hormonal regulatory circuit (Dusso et al., 2005). 

The influence of good vitamin D levels on robustness and immune function

The question of the required 25-OH-D3 titer arises already at weaning. In 2014, Weber et al. investigated the vitamin D titer of sows that received either 2,000 IU D3 or 50 µg 25-OH-D 3. They also determined the 25-OH-D3 content in the blood of the piglets of these sows. The piglets were fed exclusively colostrum and sow's milk during rearing. Until weaning, only a low concentration of 25-OH-D3 could be detected in the blood (Figure 1).

In this context, the option of offering piglets an additional source of vitamin D in the farrowing pen to prevent deficiency symptoms is also being discussed. Madsen et al. 2023 take up this idea in a recent study, which shows that even when the statutory maximum limits are fully utilised, this does not necessarily guarantee optimal provision. This study also demonstrated that piglets only absorb very small amounts of vitamin D3 via colostrum and milk. Supplementation with 25-OH-D3 during the suckling phase led to higher 25-OH-D3 plasma levels on weaning day in the test group compared to the supply of conventional vitamin D3. In a subsequent experimental E. coli challenge of both groups, the 25-OH-D3 level in the experimental group fell less sharply (-35.4% vs. -40.3%). The authors suggest that the higher vitamin D levels in the 25-OH-D3 group may contribute to improved immune resilience or a greater ability to fight E. coli infection. The results are consistent with the work of Konowalchuk et al. (2013). This study showed that additional supplementation of 50 µg/kg 25-OH-D3, with a basic supply of 1,500 IU vitamin D3 in the feed, led to a more pronounced increase in leukocyte counts than in the group that received the same amount of vitamin D3 (2,000 IU) in addition. Which target value should be aimed for in nursery piglets is the subject of current research.

25-0H-D3 reference values for fattening pigs and results of a European survey on the vitamin D status

One of the reasons why there is insufficient information available on what vitamin D titer is adequate and what is insufficient is that the 25-OH-D3 level in the blood is rarely determined in practice. For this reason, dsm-firmenich has evaluated studies (references available on request) from the last 25 years on vitamin D supply in order to be able to make recommendations (Table 1) for the vitamin D supply of fattening pigs and sows (Wiemann et al. 2024). With the help of a new method for determining vitamin D status, it is possible to assess the vitamin D levels of a very large population of fattening pigs. In this procedure, a few drops of whole blood from the ear vein are fixed on so-called "dried blood spot cards" and analyzed later. This formed the basis for a comprehensive European survey in which a total of 1,512 fattening pigs from 112 farms in 16 European countries were sampled. The vitamin D source used in the feed (D3 or 25-OH-D3) and the actual supplementation level were also taken into account. The results show clear differences between countries and between feeding systems. The majority of the animals had values below the physiologically desirable range (Table 1).

The average 25-OH-D3 level was 27.3 ng/ml, with median values of 24.8 ng/ml (Figure 2). 

More than two-thirds of the animals were either inadequately supplied or showed a clear deficiency. Only a very small proportion achieved levels associated with an optimal metabolism and immune system. lt was noticeable that animals fed exclusively with vitamin D3 predominantly had insufficient or deficient 25-OH-D3 concentrations, while animals with 25-OH-D3 supplementation via their feed achieved significantly higher blood levels. In addition, there were considerable differences in vitamin D status between the participating countries. The available data show us that a large proportion of the pig population in Europe has insufficient or deficient vitamin D levels. Improved supply, particularly through the use of 25-OH-D3, can help to improve vitamin D status in the long term. As a result, a physiologically based feeding regime is increasingly becoming the focus of modern pig production.

This article was published in Feed Magazine – Kraftfutter, issue 3–4/2026.