Vitamin D supplementation strategies

Little is known about the potential effects of this vitamin on resiliency and robustness in pigs

By Danyel Bueno Dalto, J. Jacques Matte and Jérôme LapointeThe ban on the prophylactic use of antibiotics and the restrictions on the use of pharmacological levels of dietary zinc oxide bring unprecedented challenges to the pig industry, especially during the post-weaning period. Weaning stress is frequently followed by a high incidence of intestinal disturbances, bacterial infections, antioxidant unbalances and energetic deficiencies that lead to important losses to the industry [1, 2]. In this context, vitamins nutrition can be an important tool considering their redox and/or immune modulatory effects [3], which could help to ensure robustness of newly weaned piglets.In addition to the well-known role of vitamin D on bones metabolism, in the last decades, many studies have reported other important metabolic functions of this vitamin. According to Matte and Lauridsen [4], sub-optimal vitamin D provision may compromise the immunoregulatory functions at the sites of inflammation whereas there are evidences that vitamin D upregulates the expression of genes related to energy metabolism in the mitochondria. In humans, several studies consistently found an association between low vitamin D levels and increased susceptibility to infections whereas pre-challenge supplementation was related to lower infection rates, lower severity, and reduced use of antibiotics [5, 6]. However, little is known about the potential effects of this vitamin on resiliency and robustness in pigs. According to Matte and Audet [7], the perinatal transfer (placenta and colostrum) of vitamin D in pigs is limited. A recent study of our lab reported that oral supplementation with 25-hydroxycholecalciferol (25(OH)D₃) in early life rapidly enhanced serum concentration of 25(OH)D₃ in suckling piglets but failed to keep these high status until weaning. In contrast, the exposition to UVB light was efficient in securing high 25(OH)D₃ concentrations at weaning. Therefore, it is reasonable to hypothesize that ensuring optimal vitamin D nutrition to pre- and post-weaning piglets may improve their robustness and growth performance. The present study evaluated the impact of different vitamin D supplementation strategies to pre- and post-weaning piglets on vitamin D metabolism, health markers and growth.Two vitamin D supplementation strategies were used to suckling and nursery piglets: CTR – no supplementation during the suckling period + 2000 IU/kg of vitamin D as cholecalciferol after weaning; and VD - oral 25(OH)D₃ solution (d2, 8 and 21) and UVB light exposure (d14, 16, 18 and 20) during the suckling period + 2000 IU/kg of vitamin D as 25(OH)D₃ after weaning. At weaning (d21), d28 and d35 blood and tissue samples were collected for the determination of vitamin D concentrations and the expression of genes of interest.The efficiency of UVB light exposure to maintain a high concentration of 25(OH)D₃ and 1,25(OH)₂D₃ has been demonstrated before in pigs [8] and dietary 25(OH)D₃ was reported to be better absorbed at the intestinal level and to have greater bioavailability than other sources of vitamin D [9, 10]. According to Galliot et al. [8], oral supplementation with 25(OH)D₃ at day 2 and 8 after birth rapidly enhanced serum concentration of 25(OH)D₃ in suckling piglets but these levels were not maintained until weaning. However, piglets exposed to UVB light during 15 minutes every second day from day 2 after birth had the highest serum concentration of 25(OH)D₃ at weaning. In our study, the combined oral 25(OH)D₃ + UVB supplementation strategy during the suckling period increased by 2.8-fold the serum 25(OH)D₃ concentration of piglets at weaning, compared to non-supplemented piglets, but these levels slightly decreased to 2.2-fold at day 35 (Figure 1). Considering that any residual effect of the UVB exposure on serum vitamin D would have faded out at day 35, the 2.2-fold difference between treatments at day 35 supports the better absorption/bioavailability of dietary 25(OH)D₃ compared to cholecalciferol.

Figure 1. Serum 25(OH)D3 concentrations (ng/ml) in weanling piglets according to dietary treatments and age.

According to our genes expression results, these differences in serum vitamin D concentrations between treatments would be due to changes in amount of the active form of the vitamin produced in the kidney and not to the amount of the circulatory form of vitamin D produced by the liver. In fact, the combination of 25(OH)D₃ + UVB supplementation may establish a better balance between utilisation and degradation of the active form of vitamin D. Despite the greater circulatory vitamin D concentrations in VD piglets, at weaning (day 21) the gene related to the degradation of the active form of the vitamin was down-regulated whereas at day 28 the gene related to its synthesis was up-regulated. At day 35, where the residual effects of UVB exposure were likely faded out, our results suggest lower utilization and greater degradation of the active vitamin D form.Although many studies have described effects of vitamin D, specially in the form of 25(OH)D₃, on the different aspects of the immune response in various tissues[11, 12], our study did not detect such effects, which could be due to the optimized experimental conditions that have not provided enough stimulus to the immune system. However, our genes expression results show beneficial effects on the hepatic redox balance as well as on ATP production in the mitochondria, suggesting better health status in VD piglets through lower oxidative stress levels and more available energy at the cellular level. Despite the greater vitamin D status in VD piglets, no beneficial effect of treatment was detected on growth performance of healthy piglets at weaning and during the post-weaning period. In fact, not the direct supplementation of suckling piglets but maternal vitamin D supplementation appears to be more efficient in impacting piglets growth performance [11, 13]. However, despite the higher vitamin status in VD piglets, the serum 25(OH)D₃ concentration in CTR animals increased with time, indicating that the use of 2000 IU/kg of vitamin D, independently of source, may fulfil the requirements for this vitamin in healthy piglets. Conclusions
The overall results indicate that 2000 IU of vitamin D/kg of diet, independently of source, fulfils the post-weaning piglet requirement for this vitamin. However, the use of dietary 25(OH)D₃ may promote additional health benefits.During the pre-weaning period, oral 25(OH)D₃ supplementation combined with UVB exposure was effective in increasing serum 25(OH)D₃ concentrations at weaning whereas in the post-weaning period the dietary 25(OH)D₃ supplementation at 2000 UI/kg was more efficient than dietary cholecalciferol at similar levels. The greater vitamin D status in VD piglets apparently improved the antioxidant response of these animals but had limited effects on growth and immune system of healthy piglets.Literature cited:

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Bueno Dalto and Lapointe are research scientists and Matte is an honorary scientist, all with Agriculture and Agri-Food Canada, Sherbrooke, Quebec.