Synergistic Effects of 25-Hydroxyvitamin D3, Phytase, and Probiotics on Growth, Calcium and Phosphorus Metabolism, and Bone Development in Weaned Piglets Fed Low Ca-P Diets

Seventy 28-day-old weaned barrow piglets (Duroc × Landrace × Large White; 7.2 ± 0.20 kg) were used to determine the effects of 25-hydroxyvitamin D3 (25-OH-VD3) combined with phytase and probiotics on calcium and phosphorus metabolism and bone development. Five dietary groups were tested: basal diet + 50 µg/kg 25-OH-VD3 (CON); basal diet with 17% reduced calcium and phosphorus + 50 µg/kg 25-OH-VD3 (LCP); LCP + 50 mg/kg phytase (LH); LCP + 10 mg/kg probiotics (LC); LCP + 50 mg/kg phytase + 10 mg/kg probiotics (LHC). The experiment lasted for 31 days, including 3 days adaptation period. Apparent phosphorus digestibility was higher in the LH and LHC groups than in the CON group (p < 0.05). Bone mineral density and calcium content in metacarpal and rib bones were also higher in the LHC group compared with the CON, LCP, LC, and LH groups (p < 0.05). The jejunal mRNA expression of solute carrier family 34 members (SLC34A1, SLC34A2, and SLC34A3) members was higher in the LHC group than the CON, LCP, LC, and LH groups (p < 0.05), while the relative protein expression of the calcium-sensing receptor in the kidneys was lower in the CON group than in the LCP, LH, LC, and LHC groups (p < 0.05). Additionally, supplementation with 25-OH-VD3, either alone or in combination with phytase and probiotics, was associated with an increased abundance of beneficial gut bacteria. Overall, combined supplementation of 25-OH-VD3, phytase and probiotics enhanced bone development in weaned piglets fed a low-calcium, low-phosphorus diet by improving calcium and phosphorus utilization and calcium–phosphorus metabolic regulation.