11/8/2022:  Vitamin D3 is extremely important for bone metabolism and bone development, the muscles and general immunity to infectious diseases. In recent years, the Veekijker for swine has received many questions about lameness, particularly in finishers and growers. There can be many different reasons for lameness. Lameness cases are probably also partially a result of a vitamin D3 deficiency.

Within animal health monitoring, GD regularly conducts studies to clarify signals from the field. Sometimes this also allows us to rule out that certain problems are caused by infectious diseases. A clear understanding of the role played by vitamin D3 in lameness is therefore important.

Outdated standard?

Vitamin D3 is formed in the skin when exposed to sunlight. As swine generally see little sunlight, vitamin D3 is always added to their feed. Feed producers may use a maximum of 2,000 IU of cholecalciferol per kilogram of feed. This standard came into being in the 1970s, but the feed conversion and growth of finishers has increased considerably since then. Moreover, sows also produce more piglets. This feed standard is therefore probably somewhat low for the current swine farming sector. Previous blood tests have shown that the serum concentrations of vitamin D3 in swine are variable and deficient relatively often. In this context, the relationship to lameness was noticed.

Study of D3 status

In consultation with the Supervisory Committee for Swine Health Monitoring, further proof is required for an increased European standard for vitamin D3 in swine feed. GD has therefore started by conducting a small-scale study into slaughter swine. Blood samples from more than 50 farms were tested for vitamin D3 in early 2021. Farmers cooperated enthusiastically with this study, which also collected data on farm management and feeding. The general situation was very reasonable, though there were major differences between the farms. Nine farms were found to be under the minimum. At farms where swine had outdoor access, they had clearly higher levels of vitamin D3 in their blood. Probably because these swine can generate their own vitamin D3 in the skin when exposed to sunlight.

Manageable, but not simple

The current standard for vitamin D3 in swine feed seems to provide sufficiently high levels of vitamin D3 in the blood of slaughter swine, though not necessarily everywhere. Some premixes contain more easily absorbable vitamin D3 than others. There are signs that recently weaned piglets and recently transferred finishers receive insufficient vitamin D3 in practice. Extra research is also required into sows with large litters. If sows receive insufficient vitamin D3 when farrowing, there is a greater risk of them farrowing slowly and producing weaker piglets. Further research is required into the blood levels in other age categories.

D3 deficiency often found in lame young finishers

Karlijn Eenink: swine veterinarian at GD

“Many of the questions received by the Veekijker relate to stiffness and lameness in heavier piglets and finishers in the first half of the finishing period. We are often informed that the animals only react poorly to antibiotics, while painkillers are somewhat effective. The animals generally grow out of these problems, but the damage to animal welfare and performance is already done. It is uncomfortable for the animal and it costs a great deal of time and growth capacity.

If we suspect vitamin D3 efficiency, we do a blood test. Vitamin D3 affects the calcium metabolism, so we therefore generally also check whether the blood contains sufficient calcium and phosphate. We also often check certain biomarkers in order to determine whether a young, growing animal has sufficient bone development. As D3 deficiencies are already quite commonly known in practice, we regularly receive questions about which groups of animals and how many of them should be sampled in order to get good insight.

Vitamin D3 is important for bone metabolism and for immunity to infectious diseases such as respiratory infections. As most swine see little to no sunlight and therefore cannot produce vitamin D3 themselves, it is essential that vitamin D3 is added to their feed. Once the vitamin D3 contained in the feed has been absorbed in the body, there are still two processes it must undergo. Firstly in the liver and subsequently in the kidneys. Only then does it take on the form that is suitable for the body.

Vitamin D3 can also be given in the form produced following the initial conversion in the liver. That removes the need for one of the conversion processes and usually demonstrates higher levels of D3 in the blood. Feedback from the field is that it also results in less lameness. Of course we prefer to underpin such findings with research. Early in 2021 therefore, blood tests were carried out on slaughter swine from 56 farms. As follow-up, we called the ten farms with strikingly low and strikingly high levels of vitamin D3. The difference was shown to be mainly related to the use of a certain vitamin D3 premix.

Furthermore, farms with higher D3 levels experienced fewer respiratory problems, reported less lameness, and the swine themselves showed better growth rates. However, due to the small number of farms in the study, it is possible that these differences are a coincidence. We would therefore like to do more research into this important vitamin and its effects on swine health.”

We need to be aware of the complexity of lameness issues

Johan Hulzing: swine veterinarian and member of the Supervisory Committee for Swine Health Monitoring on behalf of the KNMvD

“The reason for this study into vitamin D3 were clinical signs in the legs, in both finishers and weaned piglets. At the same time, we were seeing good results using a special premix with a more easily absorbable form of D3. In the pilot, the conventional farms fed approximately 50 percent of dry food and 50 percent gruel. We saw no significant difference between them. That could have been feasible, because the pelleting process of dry food can result in vitamin loss. However, the vitamin D3 level in the feed was insufficient at a few of the conventional farms. Many of these farms shared the same feed supplier, who has since been approached regarding this issue. In contrast, the vitamin D3 level at a few of the other conventional farms was quite high. And we found an even higher level at organic farms. Even in early spring, free-ranging pigs apparently still produce vitamin D3 when exposed to sunlight.

This pilot has not proven that the standard for D3 in swine feed must be increased. However, there may be insufficient absorption of D3 in some cases. Feed producers must therefore take these signals seriously. Bone metabolism is a complex process in which calcium, phosphor, vitamin D3 and vitamin E all play a role. The source of these minerals and vitamins is also important. If calcium is derived from a poor source, such as chalk, it is a lot less easily absorbable. If a feed supplier does not have a good calcium source, but the pig farmer does feed easily absorbable vitamin D3, the farmer can still experience problems. And if sows absorb insufficient vitamin D3, calcium and phosphorus, this will have consequences for the bone metabolism of their piglets. Any attempts to correct this in the feed of the weaned piglets, will be too late. The pelleting process of dry food can result in vitamin loss, and a low pH of gruel can result in reduced absorption. The feeding process is therefore quite tricky in practice.

Lameness caused by vitamin D3 deficiency is not a common problem, but if lameness numbers increase, this is something that should come to mind. Such signals must be taken seriously by having blood tests done and possibly necropsies. A single lame animal will currently not always result in a full blood test being done for all the pigs. However, if you wish to prove a causal relationship with the bone metabolism, blood tests are essential in representative animals that have become acutely lame. Be aware of the complexity of this issue and make sure that D3 deficiency is on your radar.”