The Triennial Growth Symposium at JAM 2013 covered a fascinating array of relevant challenges, concerns, and possible solutions related to the role of vitamin D in animal production. A primary problem that faces the swine production industry results from the fact that pigs raised in a commercial setting are housed in enclosed buildings, rather than outdoors. This production system utilizing indoor confinement does not provide exposure to sunlight, which is required for de novo
production of vitamin D.
The inability of animals living in confinement to produce their own vitamin D means that vitamin D must come from the diet, and in the case of piglets, from the sow during gestation and transfer via colostrum and milk followed by the supplied feed. C. Lauridsen noted that the transfer of vitamin D from sows to piglets via colostrum and milk does not appear to be very efficient. This means that piglets, which are only born with serum concentrations equal to 20-40% of the sow’s serum vitamin D concentrations with an additional 20% of the sow’s serum vitamin D concentrations gained from colostrum, could be at risk for development of hypovitaminosis D.
D. M. Madson, of Iowa State University’s department of veterinary diagnostic and production animal medicine, became interested in a specific problem related to hypovitaminosis D in 2010 when an accidental omission of vitamin D from feed coming from a feed supplier began to manifest itself with signs of hypovitaminosis D in piglets in the Midwest. Hypovitaminosis D in these piglets was confirmed a few months later when piglets suffering from mortality as well as nervous disorders were tested and found to have no detectable serum 25-hydroxyvitamn D. Vitamin D is required for adequate calcium absorption, so ultimately the cause of mortality and nervous disorders in these piglets was a result of hypocalcemia, but the underlying cause of this rise in piglet mortality was hypovitaminosis D. This feed was later recalled, but this accident that resulted in feed devoid of vitamin D inspired Madson, as well as veterinarians and other researchers, to investigate the problem further.
To establish the “normal” serum 25-hydroxyvitamin D levels, Madson evaluated a group of pigs that had had been living outdoors with full exposure to sun and found that those pigs had serum concentrations of 25-hydroxyvitamin D of 50 ng/ml or higher. When compared, those serum 25-hydroxyvitamin D concentrations from pigs living outdoors to 2,700 pigs living in confinement, it was observed that the average serum concentration of 25-hydroxyvitamin D was 20 ng/ml regardless of the age of the pig.
In animals, it was pointed out, any concentration below 15 ng/ml of 25-hydroxyvitamin D will pose a problem with bone health, and 25-hydroxyvitamin D serum levels below 10 ng/ml in piglets can manifest symptoms such as sudden death and tetany. The serum concentrations of the 2,700 surveyed animals living in confinement (20 ng/ml on average) indicate that stressors incurred by the animals, such as an illness or general stress, could place those animals at risk for developing hypovitaminosis D.
Madson also evaluated the shelf life of vitamin D supplements and found that this supplement degrades over time in storage and, therefore, should not be purchased as a “bulk”product. Purchasing vitamin D more frequently and storing it for less time helps to ensure accurate delivery of the intended amount of Vitamin D in the feed.
Recently, through combined efforts of feed producers, nutritionists, and veterinarians, cases of vitamin D deficiency have declined. Increased feed formulation quality control measures, diet formulations of 5-8 times NRC requirements of vitamin D, as well as availability of oral supplementation of vitamin D to piglets have reduced the occurrence of clinical cases of vitamin D deficiency in commercial swine operations. C. Lauridsen pointed out that these supplements may be of use as a result of the poor transfer of vitamin D to piglets via colostrum and milk.
It is likely that vitamin D status of pigs raised in a commercial setting will need to receive continued attention and monitoring from veterinarians, nutritionists, researchers, and producers to avoid future problems and to maximize productivity. In addition, quality control measures for the feed, with regards to vitamin D content, for these animals raised in confinement will need to be continued, the researchers said.
Eric Testroet is an M.S. student studying molecular and biochemical nutrition at Iowa State University.