Vitamin D is known as the “sunshine vitamin” because it’s produced in the skin when exposed to sunlight. For this reason, people in Denmark are recommended to take vitamin D supplements during the winter months, and vulnerable groups are advised to take them year-round. Similarly, our livestock also need vitamin D. Animals kept indoors have limited access to sunlight and therefore lack active vitamin D in their bodies unless it is provided through their feed.

Vitamin D is important for maintaining calcium and phosphorus balance, building and maintaining bones, and strengthening the immune system.

Calves are born with low vitamin D levels

In Denmark, newborn calves have very low levels of vitamin D. Data from AU Viborg show that calves are born with less than 10 micrograms of active vitamin D per liter of blood—far below the recommended level of 30–50 micrograms. Both Danish and American studies indicate that this deficiency persists as the calves grow.

“We can’t conclude that calves are born deficient, but in nature the sun is the primary source of vitamin D,” explains Saman Lashkari, who is assistant professor at Aarhus University, Department of Animal and Veterinary Sciences. He leads the ‘KalveD’ project, funded by the Danish Cattle Levy Fund. In this project, researchers will investigate whether adding vitamin D to milk replacer can raise blood levels and improve calf health.

Stillborn piglets – A major challenge

Around 44% of piglet mortality is due to stillbirths. On average, each sow has 1.9 stillborn piglets per litter—a number that has increased since 2019. This affects both animal welfare and farm economics.

The ‘CALMIN’ project, supported by the Danish Pig Levy Fund, will examine whether calcium and vitamin D supplementation for pregnant sows can reduce stillbirths and improve the vitality of live-born piglets and health status of the sow. The project is led by Takele Feyera, who is assistant professor at Department of Animal and Veterinary Sciences and has long studied the impact of nutrition on piglet survival.

Small supplements – Big impact

Both projects are based on the idea that vitamin D can enhance animal health and productivity. For calves, the focus is on addressing deficiencies during the first weeks of life, when the immune system, bones, and muscles are developing. In pigs, the focus is on both vitamin D and calcium. The aim is here to improve uterine contractions during farrowing, shortening labor and reducing the risk of stillbirths.

KalveD project: Focus on immunity and growth

Researchers will test different doses and sources of vitamin D in milk replacer. Calves will receive either conventional D₃ or 25-OH-D₃ in low, medium, or high doses from day two after birth until weaning at 70 days. Their weight, feed intake, and health will be monitored, along with blood levels of vitamin D and immune response.  “We want to investigate whether extra vitamin D can boost the immune system to make the calves more resistant to disease,” says Saman Lashkari. 

Boosting the immune system

Recent research shows that vitamin D activates immune cells and promotes substances that protect against infections. Adequate levels may reduce disease and improve herds’ health. “There are few international studies showing that high blood levels of vitamin D in calves are linked to better immune function,” Lashkari notes. “However, these are performed under totally different conditions, and we need to investigate whether this holds true under Danish conditions”, he adds.

CALMIN Project: Shorter farrowing and better survival

In the CALMIN project, one group of sows receives vitamin D and calcium supplements according to current standards. Another group receives 31% more calcium and 2.5 times more vitamin D₃. The researchers measure the duration of farrowing and the number of stillborn piglets.

In addition, they collect a wide range of samples for detailed analyses. Together, these will provide insights into both the sows’ and piglets’ vitamin D status, well-being, health, and robustness. “We’ll gain detailed insights into the physiological stress experienced by sows and piglets during farrowing. This is crucial for improving feeding strategies in practice,” says Takele Feyera.

Muscle Function – including the uterus

Vitamin D regulates calcium in muscle cells and affects their ability to contract and relax. Weak muscles in young animals can be early signs of deficiency. In pregnant sows, uterine muscle function is central to the CALMIN project. Researchers believe the uterus may become fatigued and fail to contract effectively during long farrowing sessions. “Studies in humans and rats have shown a link between blood calcium levels and labor duration,” explains Feyera. “As a new aspect in this project we’re also looking at the sow’s recovery after farrowing -something that hasn’t been studied before,” he continues.

Calcium and oxytocin – A crucial interaction

During farrowing, the hormone oxytocin plays a key role by triggering uterine contractions through the release of calcium from the uterine muscle cells. However, prolonged exposure can make the uterus less responsive to oxytocin. If the sow has low blood calcium, contractions may be weak or absent, delaying or complicating labor. By increasing vitamin D and calcium intake, researchers hope to achieve shorter and more efficient farrowings.

Vitamin D, growth and strength

Vitamin D helps the body absorb calcium and phosphorus from feed. Without it, absorption is poor. Through different steps in the liver and kidneys, vitamin D is converted into its active form, calcitriol, which regulates calcium and phosphor balance in the blood and ensures that minerals are stored in the bones. If deficient, calcium is drawn from bones, weakening them. Both projects therefore examine overall robustness, and in case of the pigs also bone strength.

Practical relevance

These projects have strong practical implications. The results may lead to new recommendations for vitamin D and calcium supplementation. While it may cost farmers a bit more, it could ultimately improve productivity and animal welfare.