Different vitamin D supplementation strategies impact serum vitamin D concentrations and the mRNA expression of genes related to vitamin D metabolism, mitochondria respiration, redox balance, and immune system in weanling piglets

This study compared the effects of different vitamin D supplementation strategies to pre- and postweaning piglets on vitamin D metabolism and health-related parameters. Sixty Yorkshire-Landrace × Duroc suckling piglets were selected at the first day of age and randomly assigned to one of two vitamin D supplementation strategies (n = 30 pigs per treatment): CTR-oral saline at days 2, 8, and 21 of age and, from weaning (day 21), in-feed supplementation with 2,000 IU of vitamin D as cholecalciferol; and VD-oral 25-hydroxycholecalciferol (25(OH)D3) solution at days 2, 8, and 21 of age plus 15-min exposure to UVB light every second day from day 14 until day 21 and, from weaning, in-feed supplementation with 2,000 IU of vitamin D as 25(OH)D3. Piglets were slaughtered (n = 10 pigs per treatment/day) at days 21 (before start in-feed experimental diets), and 28 and 35 and blood and tissues samples (jejunum, liver, and kidney) were collected. Body weight (BW), concentrations of serum 25(OH)D3 and jejunum, liver, and kidney mRNA expression of genes related to vitamin D, antioxidant system, and immune defense were measured. Body weight was not affected by treatments (P ≥ 0.34). Serum 25(OH)D3 concentrations were greater for VD piglets at day 21, 28, and 35 (P < 0.01). No effect of treatment was detected (P ≥ 0.14) for mRNA expression in the jejunum mucosa. In the liver of VD piglets, mRNA expressions of genes related to the antioxidant system were lower at day 21 (NDUFB2) and at day 28 (BNIP3, GPX4, and MSRA) (P ≤ 0.10). The mRNA analysis in kidney during the overall period detected higher expression of genes related to the mitochondria oxidative phosphorylation (COX17, NDUFB2, and NDUFB6) in VD groups compared with CTR (P ≤ 0.09). The expression of CYP27B1 in kidney was higher at day 28 and CYP24A1 was lower at day 21 but higher at day 35 for VD animals. In conclusion, during the preweaning period, dietary 25(OH)D3 supplementation combined with UVB exposure was effective in increasing serum 25(OH)D3 concentrations at weaning, whereas in the postweaning period, dietary 25(OH)D3 supplementation at 2,000 IU/kg was more efficient then dietary cholecalciferol at similar levels. The overall results indicate that 2,000 IU of vitamin D/kg of diet, independently of source, may be enough to improve the vitamin D status of postweaning piglets. However, the use of dietary 25(OH)D3 may promote a better modulation of vitamin D metabolism and redox balance.

Enhancement of selectivity, 25-hydroxyvitamin D3 level, alkaline phosphatase activity and reproductive performance in gilts and primiparous sows using 14-epimer of 25-hydroxyvitamin D3

Selecting breed-worthy gilts as sow replacements is essential for continuity of pig production cycle. Though vitamin D3 (VD3) is known to enhance reproductive performance of multiparous sows, there is still a knowledge gap on its impact in developing gilts and primiparous sows. This study was aimed to quantify plasma 25-hydroxyvitamin D3 (25(OH)D3), serum alkaline phosphatase (ALP), and examine the reproductive performance of primiparous sows fed diets supplemented with regular VD3, and its 25(OH)D3 epimers. The study sample comprised 10-week-old replacement gilts (50 % Landrace x 50 % Yorkshire, N = 180) assigned in a randomized complete block design to three treatments [2,000 IU/kg of VD3 (T1), 25 µg/kg of 14‑epi-25(OH)D3, half dose (T2), and 50 µg/kg of 25(OH)D3 (T3)] equilibrated to 2,000 IU/kg in base diets. Selections occurred at 22, 27 and 35 weeks of age, respectively. Plasma 25(OH)D3, serum alkaline phosphatase (ALP), bone structure and reproductive performance were analyzed. Dietary treatments influenced carpus (P = 0.023), fore view stance (P = 0.017), infantile vulva (P = 0.014), inverted (P = 0.048), and prominent teat (P < 0.001). Post-partum 25(OH)D3 concentration and ALP activity were elevated by day 25 (P < 0.001). Treatment diets also influenced total born (P < 0.001), born alive (P = 0.048), and still born (P = 0.049). Two factors affect circulating 25(OH)D3 and ALP activity: physiological changes in sows during lactation, and dietary 25(OH)D3 intake. 14‑epi-25(OH)D3 is a potent metabolite for improving maturation of reproductive organs in developing gilts. It also reduces still birth in primiparous sows.

Effects of sources and routes of administration of vitamins A, D and copper on postnatal status of these micronutrients in piglets

Twenty-six nulliparous sows were fed conventional gestation and lactation diets supplemented (N = 13) or not (N = 13) with extra daily supplements of 25-hydroxy-cholecalciferol (25-OH-D3; 4 ĸIU), β-carotene (24 ĸIU), and copper (Cu)-proteinate (45 mg) from day 90 of gestation to 21 d of lactation (L21). In each litter, 10 piglets were divided into 5 pairs received, at 2 (L2) and 8 d (L8) of age, one of the five combinations of micronutrient sources and routes of administration (N = 260 piglets total). These neonatal treatments (N = 26 pairs or 52 piglets each) consisted of oral vitamin D3, retinol acetate and CuSO4 (T1); oral 25-OH-D3, β-carotene, and Cu proteinate (T2); exposure to ultraviolet light (UVB), oral retinol palmitate and Cu gluconate (T3); intramuscular vitamin D3 and retinyl propionate and oral Cu acetate (T4); oral saline (CTRL). Oral or intramuscular provisions corresponded to 12 mg of Cu and 70 and 12 ĸIU of vitamins A and D, respectively. Blood samples were collected from all piglets at L2, L8, and L21 for determination of serum Cu, retinol, and 25-OH-D3. Body weight was measured at birth, L2, L8, and L21. Piglets were weaned at L21, and liver and blood samples were collected 2 d later to evaluate oxidative enzymes in blood and liver and hepatic ATP concentrations and expression of genes associated with antioxidant status. Sow treatments had marginal or no impacts on Cu, retinol, 25-OH-D3, or antioxidant status in piglet blood serum and liver. However, when supplements were given to piglets, hepatic Cu was 38% greater in for all treated piglets compared to CTRL (P < 0.01), hepatic retinol was 3 times higher in T1 than in CTRL (P < 0.01) and intermediate for other treatments whereas serum 25-OH-D3 was markedly increased with T2 and T3 at L8 and L21, respectively, compared to CTRL (Piglet treatment × Age interaction, P < 0.01). Concerning antioxidant activities, glutathione peroxidase, and superoxide dismutase were increased (P < 0.03) in plasma of T2 piglets whereas the highest values (P < 0.03) for indicators of oxidative damage to proteins were observed in T4 piglets. The study revealed that oral Cu proteinate from T2, oral retinol acetate from T1, oral 25-hydroxy-cholecalciferol from T2, and UVB light exposure from T3 were the most efficient ways of increasing the postnatal status of these micronutrients in suckling piglets and this may have some impacts on their peri-weaning antioxidant status.

Effect of supplementation of vitamin D3 or vitamin D2 on serum concentrations of free and total 25-hydroxyvitamin D and the expression of genes involved in immune function in peripheral blood mononuclear cells of weaned pigs

The present study aimed to compare the effects of vitamin D₂ and vitamin D₃ supplementation on concentrations of total and free 25(OH)D in plasma and the expression of genes involved in the innate immune system in peripheral blood mononuclear cells (PBMC) in weaned pigs. Five groups of pigs (with an initial body weight of around 9 kg) received basal diets supplemented with either 500 (control group), 1000 or 2000 IU vitamin D₃/kg diet or 1000 or 2000 IU vitamin D₂/kg diet for a period of 4 weeks. Vitamin D supplementation did not influence feed intake, body weight gain, feed conversion ratio, apparent total tract digestibility of calcium and phosphorus, and serum concentrations of calcium, inorganic phosphate and parathyroid hormone. Supplementation of vitamin D₃ led to a dose-dependent increase of the concentrations of total and free 25(OH)D in serum. In contrast, pigs supplemented with 1000 or 2000 IU vitamin D₂/kg diet did not have higher concentrations of total and free 25(OH)D in serum than the control group. The ratio of free/total 25(OH)D in serum was not influenced by vitamin D₃ supplementation, whereas the group supplemented with 2000 IU vitamin D₂/kg diet had a higher free/total 25(OH)D ratio than the groups supplemented with 1000 or 2000 IU vitamin D₃/kg diet. Genes involved in vitamin D signalling (CYP27B1, VDR), as well as pro-inflammatory and immune regulatory genes (TLR4, TNF, IL1B and TGFB1) and genes encoding porcine protegrins (NPG1, NPG4), proteins belonging to the group of antimicrobial peptides, in PBMC were not different among groups supplemented with vitamin D₃ or vitamin D₂ and the control group. Therefore, the study indicates that supplementation of vitamin D₂ causes much lower levels of total 25(OH)D than supplementation of vitamin D₃ and that supplementation of vitamins D₂ or D₃ at moderate levels does not have an impact on the innate immune function in healthy pigs.

Impact of supplementation with dihydroxylated vitamin D3 on performance parameters and gut health in weaned Iberian piglets under indoor/outdoor conditions

BACKGROUND

Vitamin D may improve innate antimicrobial response and the integrity of the intestinal mucosal barrier representing an alternative to antibiotics for improving pig health. Therefore, benefits of dietary supplementation with a product based on vitamin D₃ metabolite-rich plant extracts were assessed in 252 purebred Iberian piglets for a period of 60 days. The study group received 1,25 dihydroxyvitamin D (1,25(OH)₂D) (100 ppm) in the conventional feed, which already included vitamin D (2000 IU in the starter and 1000 IU in the adaptation diets, respectively). Average daily gain (ADG), feed conversion ratio (FCR) and coefficient of variation of body weight (CV-BW) were assessed along the study. Blood samples, from 18 animals of the study group and 14 animals of the control group, were collected at selected time points to determine white blood cell count, concentration of vitamin D₃ and its metabolites, and IgA and IgG in serum. Histopathology, morphometry, and immunohistochemistry (IgA and FoxP3) from small intestine samples were performed on days 30 and 60 of the study from 3 animals per group and time point.

RESULTS

The ADG (493 vs 444 g/day) and FCR (2.3 vs 3.02) showed an improved performance in the supplemented animals. Moreover, the lower CV-BW indicated a greater homogeneity in the treated batches (13.17 vs 26.23%). Furthermore, a mild increase of IgA and in the number of regulatory T cells in the small intestine were observed in treated pigs.

CONCLUSIONS

These results highlight the benefits of this supplementation and encourage to develop further studies along other production stages.

Sow Nutrition, Uterine Contractions, and Placental Blood Flow during the Peri-Partum Period and Short-Term Effects on Offspring: A Review

The birth process is a crucial event for piglet survival. Along with increasing litter sizes, not only has the duration of parturition increased, but placental blood flow per piglet has reduced and placental area per piglet has become smaller, making these piglets more susceptible for hypoxia. Diminishing the risk of piglet hypoxia by either reducing the total duration of parturition or increasing fetal oxygenation may reduce the incidence of stillbirth and early post-partum mortality. This review discusses options to do so by nutritionally supporting the sow in the final pre-partum period, after discussing the role of uterine contractions and placental blood flow. Providing sufficient energy seems to be a logical first step, but also other nutrients needed for uterine contractions, such as calcium, or enhancing uterine blood flow by using nitrate seem promising. These nutrient requirements may depend on litter size.

Effects of maternal and offspring treatment with two dietary sources of vitamin D on the mineral homeostasis, bone metabolism and locomotion of offspring fed protein- and phosphorus-reduced diets

The present study aims to compare the effects of maternal and offspring treatment with 25-hydroxycholecalciferol (25-OHD₃) and vitamin D₃ on vitamin D status, mineral homoeostasis, bone metabolism and locomotion in the offspring. Either vitamin D₃ (50 μg/kg diet) or 25-OHD₃ (50 μg/kg diet) was supplemented to the gestation and lactation diets of 49 multiparous sows and/or to the diets of their growing offspring. Treatment of the sows did not affect plasma concentrations of 25-OHD₃ of the offspring. Pigs fed 25-OHD₃ had higher plasma concentrations of 25-OHD₃ than pigs that received vitamin D₃ during rearing and fattening. However, neither plasma concentrations of calcium, phosphate and bone markers during the observation period nor bone ash and bone mineral density at slaughter were clearly affected by the treatment. Maternal and offspring treatment with 25-OHD₃ instead of vitamin D₃ resulted in a slight reduction in the prevalence of leg swelling. In addition, more pigs walked with even steps and normal stride length. Further studies are needed to test whether the slight effects observed in the present experiment are reproducible and of relevance for animal health and welfare. In that case, the underlying mechanisms should be revealed in order to take advantage of potentially beneficial influences especially under certain feeding regimes.

Vitamin D Deficiency in Farm Animals: A Review

One of the most effective vitamins in the musculoskeletal structure and immune system of farm animals is Vitamin D. The widespread risk of Vitamin D deficiency states is known widely resulting in autoimmune diseases, diabetes, rickets, metabolic bone diseases, and cancers. The aim of this review is to address the subject of Vitamin D deficiency in farm animals and the role of vitamin D in health and deficiency states. Although Vitamin D deficiency is generally defined as < 20 ng/mL in serum, but this level remains to be discussed. Vitamin D synthesis in the skin is the major source of Vitamin D in the body and is influenced by genetic and several environmental factors, such as length of sun exposure, season, and latitude. Sun exposure might be limited during winter in some areas, such as northern latitudes. Thus, food sources can play essential roles in supplying the demand for vitamin D. Some animal species have more sensitivity to Vitamin D deficiency due to their different metabolism, homeostasis, and adaptation to specific diets and environments. Farm animal species, such as cattle, pigs, llamas, Alpacas, small ruminants, and broiler chickens are more sensitive to Vitamin D deficiency. However, some farm animal species including horses and donkeys usually have a low risk of Vitamin D deficiency. Therefore, the management of Vitamin D deficiency and its consequences are critical in some species. The inclusion of Vitamin D in the body of farm animals depended on farming practices, sun exposure in different seasons, and the content of diets. Due to the diversity of species, regulation of many ongoing processes in animals’ bodies, the complexity of Vitamin D metabolism, and different metabolites, more studies are necessary to find the vital roles of vitamin D in the prevention and control of diseases in farm animals.

Dietary supplementation of 25-hydroxycholecalciferol as an alternative to cholecalciferol in swine diets: A review

25-hydroxycholecalciferol (25-OHD₃ ) formed via hepatic hydroxylation from vitamin D, cholecalciferol, represents the precursor of the biologically active vitamin D hormone, 1,25-dihydroxyvitamin D. Due to a higher absorption rate and the omission of one hydroxylation, dietary supplementation of 25-OHD₃ instead of vitamin D₃ is considered to be more efficient as plasma concentrations of 25-OHD₃ are increased more pronounced. The present review summarises studies investigating potential beneficial effects on mineral homeostasis, bone metabolism, health status and performance in sows, piglets and fattening pigs. Results are inconsistent. While most studies could not demonstrate any or only a slight impact of partial or total replacement of vitamin D₃ by 25-OHD₃ , some experiments indicated that 25-OHD₃ might alter physiological processes when animals are challenged, for example, by a restricted mineral supply.

Supplementing sows with the leucine metabolite beta-hydroxy-beta-methylbutyrate and vitamin D3 improves piglet birth weights that may lead to increased weaning weights

Previous university studies demonstrated that supplementing sows with calcium beta-hydroxy-beta-methylbutyrate (CaHMB) in late gestation and/or lactation improved piglet weights through weaning. Two studies were conducted at commercial farrowing operations to test if the results would translate to commercial operations. Sows in both trials were randomized to receive either 3 g/day CaHMB plus 500 IU/day vitamin D3 (HMB/D) or a calcium carbonate containing control top-dressed to the feed from day 104 of gestation through weaning. Sows were randomly assigned to either HMB/D (n = 41 trial 1 and n = 26 trial 2) or control (n = 46 trial 1 and n = 26 trial 2). Data were analyzed using a general linear model with main effects of group, treatment, and group by treatment interaction. Treatment with HMB/D had no effect on sow weights, lactational weight loss, and stillborn or mummified piglets. In trial 1, the control group had an increased number of live born piglets, which at 24 h tended to be greater, and no difference in liveborn or 24-h piglet numbers was seen in trial 2. In trial 1, HMB/D increased piglet live birth (P &lt; 0.03) and 24-h weights (1,490 ± 30.1 vs. 1,390 ± 28.8 g in HMB/D and control piglets, respectively, P &lt; 0.02). Farm practices were to equalize piglet numbers across sows by cross-fostering. After cross-fostering, the 24-h average piglet weights were not different, and further advantages to supplementation were not observed (P = 0.21). In trial 2, birth and 24-h weights of the piglets from HMB/D-supplemented sows were increased (P &lt; 0.0001). Piglets from sows supplemented with HMB/D were 9.7% heavier at birth and 9.2% heavier at 24 h (1,549 ± 22.0 and 1,419 ± 21.2 in HMB/D and control, respectively). A difference was observed in weaning age (P &lt; 0.0001), and weaning weights were adjusted to 21-day weights (5,426 ± 103.5 and 5,205 ± 99.5 for HMB/D and control piglets, respectively, P = 0.12). Analysis by group showed that HMB/D tended to increase weaning weights in younger sows (second and third parity), 5,432 ± 150.7 and 5,074 ± 142.7 in HMB/D and control piglets, respectively (P &lt; 0.09). In conclusion, these results agree with previous university studies demonstrating that CaHMB supplementation increased early piglet weights with a tendency to improve weaning weights.

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

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 D3/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 D3. However, the bone markers CrossLaps and osteocalcin were not affected. Overall, the present results suggest that sows fed 25-hydroxycholecalciferol instead of vitamin D3 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.

Maternal VD3 supplementation during gestation improves intestinal health and microbial composition of weaning piglets

Vitamin D₃ (VD₃) has been reported to improve the reproductive performance of sows. This study was conducted to investigate the long-term effect of maternal VD₃ supplementation during gestation on the intestinal health of piglets. Twenty-three Landrace × Yorkshire gilts were randomly allocated into two groups to receive one of the following two diets during gestation: basal diet (CON group, 800 IU VD₃ per kg diet, n = 12) and VD₃ supplemented diet (VD₃ group, 2000 IU VD₃ per kg diet, n = 11). All sows were then fed with the same diet during lactation. Results showed that maternal VD₃ supplementation during lactation tended to decrease (p = 0.08) the body weight loss of sows during lactation compared to the CON group. Besides, the relative length and weight of the small intestine (SI) and the villus height of the duodenum and ileum in weaning piglets were much higher (p < 0.05) in the VD₃ group than those in the CON group, though their body weight was not changed. Meanwhile, maternal VD₃ supplementation significantly upregulated the expression levels of IGF-1, IGF-2R, VDR, GLUT-2 and CAT1 in the duodenum (p < 0.05), and increased the expression levels of IGF-1, IGF-1R, IGF-2R, VDR, Occludin, ZO-1, MUC2, PEPT1 and CAT1 (p < 0.05) in the jejunum of suckling piglets compared with the CON group. Besides, the concentration of SigA in the jejunum of suckling piglets was higher (p < 0.05) in the VD₃ group than that in the CON group. In addition, maternal VD₃ supplementation significantly increased the contents of short chain fatty acids and the relative abundance of Lactobacillus and Faecalibacterium (p < 0.05) in the feces of weaning piglets compared to the CON group. Moreover, the relative abundance of unidentified_Lachnospiraceae in the feces of weaning piglets tended to be higher (p = 0.05), while that of unidentified_Spirochaetaceae was lower (p < 0.05) in the VD₃ group than those in the CON group. Taken together, maternal VD₃ supplementation during gestation could improve the intestinal function and microbiota in suckling piglets.

Effect of 1,25-Dihydroxyvitamin D3-Glycosides on the Farrowing Process and Piglet Vitality in a Free Farrowing System

Vitamin D improves the reproductive efficiency in animals. This study aimed to examine the effects of 1,25-dihydroxyvitamin D3-gylcosides (1,25-vitD) on the farrowing process in sows and the vitality of their piglets. In total, 100 sows were allocated into two groups at insemination (‘1,25-vitD’ and ‘negative control’). The 1,25-vitD group received 260−300 mg/sow/day 1,25-vitD in their feed during the gestation period. Backfat thickness, fecal score, and the farrowing process was evaluated. The piglets were categorized into live born or stillborn, and vitality was evaluated by assessing the umbilical cord and the meconium score. The number of total-born piglets in sows of ‘1,25-vitD’ was higher and the farrowing duration was shorter than in the negative control group without showing significance in the univariable analysis. In a linear multiple regression model including the variables ‘farrowing duration’, ‘total born piglets’ and ‘1,25-vitD’ differences became evident. We found that 1,25-vitD was associated with a reduced farrowing duration (p = 0.055). Moreover, significantly more mummies (p < 0.01) and short ruptured umbilical cords (p < 0.05) were observed in the 1,25-vitD group. This study showed an effect of 1,25-vitD on the farrowing process. However, more research is needed to better describe the mechanism of 1,25-vitD in detail.

Use of 25-hydroxyvitamin D3 in diets for sows: A review

Dietary supplementation with 25-hydroxyvitamin D₃ (25OHD₃), as an alternative source of vitamin D, is becoming increasingly popular due to its commercialization and more efficient absorbability. The addition of 25OHD₃ rather than its precursor vitamin D₃ can circumvent the 25-hydroxylation reaction in the liver, indicating that supplementation of 25OHD₃ can rapidly improve the circulating vitamin D status of animals. Emerging experiments have reported that maternal 25OHD₃ supplementation could increase sow performances and birth outcomes and promote circulating vitamin D status of sows and their offspring. Increased milk fat content was observed in many experiments; however, others demonstrated that adding 25OHD₃ to lactating sow diets increased the contents of milk protein and lactose. Although an inconsistency between the results of different experiments exists, these studies suggested that maternal 25OHD₃ supplementation could alter milk composition via its effects on the mammary gland. Previous studies have demonstrated that adding 25OHD₃ to sow diets could improve the mRNA expressions of insulin-induced gene 1 (INSIG1) and sterol regulatory element-binding protein 1 (SREBP1) in the mammary gland cells from milk and increase the mRNA expressions of acetyl-CoA carboxylase α (ACCα) and fatty acid synthase (FAS) in the mammary gland tissue. Maternal 25OHD₃ supplementation promotes skeletal muscle development of piglets before and after parturition, and improves bone properties including bone density and bone breaking force in lactating sows and their piglets. Interestingly, 25OHD₃ supplementation in sow diets could improve neonatal bone development via regulation of milk fatty acid composition related to bone metabolism and mineralization. In this review, we also discuss the effects of adding 25OHD₃ to sow diets on the gut bacterial metabolites of suckling piglets, and propose that butyrate production may be associated with bone health. Therefore, to better understand the nutritional functions of maternal 25OHD₃ supplementation, this paper reviews advances in the studies of 25OHD₃ for sow nutrition and provides references for practical application.

Recent advances of vitamin D in immune, reproduction, performance for pig: a review

Vitamin D (VD) has been reported to play multiple and significant roles in improving pig health via modulating calcium and phosphorus homeostasis, skeletal muscle development and the immune system. Apart from food, photochemical action of 7-dehydrocholesterol in the skin is the main source of this molecule for pigs. The VD from dietary intake or photosynthesized via skin can be absorbed into the liver for hydroxylation, and further hydroxylated into the hormone form of VD (1,25-dihydroxyvitamin D3 or 1,25(OH)2D3) in the kidney. As a sterol hormone, 1,25(OH)2D3 is able to bind with the VD receptor (VDR), and this ligand-receptor complex (VDR/retinoic X receptor) translocates from the cytoplasm into the nucleus to regulate gene expression, thus modulating metabolism. In this review, we summarized the recent studies regarding the non-skeletal health benefits of VD for pigs, and focused on the recent advances in the cellular and molecular mechanisms of VD that affects the immune system and reproductive health. This review provides a reference for future research and application of VD in pigs.

Vitamin D Metabolism and Profiling in Veterinary Species

The demand for vitamin D analysis in veterinary species is increasing with the growing knowledge of the extra-skeletal role vitamin D plays in health and disease. The circulating 25-hydroxyvitamin-D (25(OH)D) metabolite is used to assess vitamin D status, and the benefits of analysing other metabolites in the complex vitamin D pathway are being discovered in humans. Profiling of the vitamin D pathway by liquid chromatography tandem mass spectrometry (LC-MS/MS) facilitates simultaneous analysis of multiple metabolites in a single sample and over wide dynamic ranges, and this method is now considered the gold-standard for quantifying vitamin D metabolites. However, very few studies report using LC-MS/MS for the analysis of vitamin D metabolites in veterinary species. Given the complexity of the vitamin D pathway and the similarities in the roles of vitamin D in health and disease between humans and companion animals, there is a clear need to establish a comprehensive, reliable method for veterinary analysis that is comparable to that used in human clinical practice. In this review, we highlight the differences in vitamin D metabolism between veterinary species and the benefits of measuring vitamin D metabolites beyond 25(OH)D. Finally, we discuss the analytical challenges in profiling vitamin D in veterinary species with a focus on LC-MS/MS methods.

Effects of dietary 25-hydroxyvitamin D3 supplementation on growth performance, immune function and antioxidative capacity in weaned piglets

The study evaluated the effects of different doses of 25-hydroxyvitamin D₃ (25(OH)D₃) on growth performance, immune function and antioxidative capacity in piglets. In a 21-d trial, 35 weaned pigs were divided into five groups and diets were supplemented with 5.5 (control), 43.0, 80.5, 118.0 and 155.5 μg 25(OH)D₃/kg, respectively. No treatment effects were observed for average daily gain, average daily feed intake and feed to gain ratio. Increasing dietary 25(OH)D₃ levels increased serum 25(OH)D₃ concentrations linearly (p < 0.01), decreased the frequency of CD3+CD4+ and CD3+CD8+ T cells (p < 0.01), and the serum level of complement component 3 (p < 0.05). Supplementation of 80.5 and 118.0 μg 25(OH)D₃/kg enhanced the activity of serum glutathione peroxidase (p < 0.05) and addition of 43.0 μg 25(OH)D₃/kg increased the malondialdehyde concentration (p < 0.05). Overall, feeding high-dose 25(OH)D₃ to weaned pigs partly improved immune functions and the antioxidative capacity.

The effects of maternal dietary supplementation of cholecalciferol (vitamin D3) and 25(OH)D3 on sow and progeny performance

A total of 69 sows (DNA Line 200 × 400) and their progeny were used to determine if feeding a combination of vitamin D₃ and 25(OH)D₃ influences neonatal and sow vitamin D status, muscle fiber morphometrics at birth and weaning, and subsequent growth performance. Within 3 d of breeding, sows were allotted to one of three dietary treatments fortified with 1,500 IU/kg vitamin D₃ (CON), 500 IU/kg vitamin D₃ + 25 μg/kg 25(OH)D₃ (DL), or 1,500 IU/kg vitamin D₃ + 50 μg/kg 25(OH)D₃ (DH). When pigs were sacrificed at birth, there were no treatment effects for all fiber morphometric measures (P > 0.170), except primary fiber number and the ratio of secondary to primary muscle fibers (P < 0.016). Pigs from CON fed sows had fewer primary fibers than pigs from sows fed the DH treatment (P = 0.014), with pigs from sows fed DL treatment not differing from either (P > 0.104). Pigs from CON and DL fed sows had a greater secondary to primary muscle fiber ratio compared to pigs from DH sows (P < 0.022) but did not differ from each other (P = 0.994). There were treatment × time interactions for all sow and pig serum metabolites (P < 0.001). Therefore, treatment means were compared within the time period. At all time periods, sow serum 25(OH)D₃ concentrations differed for all treatments with the magnitude of difference largest at weaning (P < 0.011), where serum 25(OH)D₃ concentration was always the greatest when sows were fed the DH diet. At birth, piglets from DH fed sows had greater serum 25(OH)D₃ concentrations than piglets from sows fed the DL treatment (P = 0.003), with piglets from sows fed CON treatment not differing from either (P > 0.061). At weaning, serum concentrations of 25(OH)D₃ in piglets from all sow treatments were different (P < 0.001), with the greatest concentration in piglets from DH sows, followed by CON, and followed by DL. There were no treatment × time interactions for any of the metabolites measured in milk and no treatment or time main effects for 24,25(OH)₂D₃ concentration (P > 0.068). Colostrum collected within 12 h of parturition contained less (P = 0.001) 25(OH)D₃ than milk collected on day 21 of lactation. Regardless of time, concentrations of 25(OH)D₃ in milk were different (P < 0.030), with the largest 25(OH)D₃ concentration from DH fed sows, followed by DL, and then CON. In conclusion, combining vitamin D₃ and 25(OH)D₃ in the maternal diet improves the vitamin D status of the dam and progeny and it increases primary muscle fiber number at birth.