Comparative Study of the Effects of Two Dietary Sources of Vitamin D on the Bone Metabolism, Welfare and Birth Progress of Sows Fed Protein- and Phosphorus-Reduced Diets

SIMPLE SUMMARY: The dietary supply of vitamin D(3), which is carried out in indoor husbandry due to limited sunlight, often results in a vitamin D status that is lower than that observed in outdoor pig farming. Studies have shown that the use of the vitamin D metabolite 25-hydroxycholecalciferol leads to a more efficient increase in vitamin D status. However, when nutrient intake is adequate, the replacement of the vitamin D source appears to have no or only marginal effects on the performance and bone metabolism of sows. The objective of this study was to investigate the influence of both forms of vitamin D, vitamin D(3) and 25-hydroxycholecalciferol, on the mineral homeostasis, bone metabolism, welfare and birth progress of sows fed protein- and phosphorus-reduced diets. Supplementation with 25-hydroxycholecalciferol instead of vitamin D(3) improved vitamin D status and reduced gait changes. However, mineral homeostasis and bone metabolism were not affected by the replacement of the vitamin D form. In conclusion, under conditions of a dietary reduction in protein and phosphorus, the replacement of the vitamin D form seems to help to improve the locomotion of sows, although bone mineralization is probably not affected. ABSTRACT: To investigate the influence of two dietary sources of vitamin D on the vitamin D status, bone metabolism, welfare and birth progress of gestating and lactating sows, forty-nine multiparous sows were randomly assigned to one of two diets: “CON” (n = 25; 50 μg vitamin D(3)/kg feed) and “HYD” (n = 24; 50 μg 25-hydroxycholecalciferol/kg feed). The basal diets were protein- and phosphorus-reduced. The trial started on day 3 ante insemination of the sows and ended with weaning of the piglets on day 28 postpartum. Dietary supplementation of 25-hydroxycholecalciferol resulted in improved maternal vitamin D status (p < 0.001), fewer gait changes (p < 0.01) and longer standing time after feeding (day 5 ante partum; p < 0.05) compared to vitamin D(3). However, the bone markers CrossLaps and osteocalcin were not affected. Overall, the present results suggest that sows fed 25-hydroxycholecalciferol instead of vitamin D(3) showed improved locomotion and stance strength. However, this outcome is probably not related to altered bone metabolism. The underlying mechanisms must be investigated in further studies.