Influence of added 1,25(OH)₂D₃-glycoside on nursery pig growth performance, bone measurements, and cytokine concentrations

A total of 2,268 crossbred pigs (L337 × 1050, PIC; initially 5.5 ± 0.18 kg) were used in a 42-d growth study to evaluate the effects of 1,25(OH)₂D₃-glycoside provided from a plant extract on growth performance, bone characteristics, and serum criteria of nursery pigs. Pigs were weaned at approximately 21 d of age and randomly assigned to 1 of the 3 dietary treatments in a randomized complete block design. A total of 84 pens were used with 27 pigs per pen and 28 replications per treatment with pens blocked by BW and date of entry into the facility. Treatment diets were corn-soybean meal-based and consisted of a control diet (1,653 IU/kg of vitamin D₃), or the control diet with 1.2 or 2.0 μg of 1,25(OH)₂D₃-glycoside/kg. Blood samples were collected from 25 gilts/treatment on days 21 and 42 to assess 25(OH)D₃, cytokine concentrations, and antibody titers. At the end of the study, 10 pigs per treatment were euthanized and the right fibula, metacarpal, second and 10th ribs were collected to determine bone density, breaking strength, and percentage bone ash. Overall, there was a tendency (linear, P = 0.067) for a reduction in G:F as added 1,25(OH)₂D₃-glycoside increased, but no significant effects on final BW, ADG, ADFI, or mortality were observed. There were no treatment × bone interactions for bone breaking strength and bone ash. Percentage bone ash increased (linear, P = 0.030) across all bones as 1,25(OH)₂D₃-glycoside increased. Treatment did not affect bone ash weight and breaking strength. Metacarpals and 10th ribs had the greatest bone ash weight followed by the fibula with the second ribs having the lowest (P < 0.05). Metacarpals had greater breaking strength compared to all other bones, followed by the fibula and 10th rib, with the second rib having the lowest (P < 0.001). There was a bone × treatment interaction for bone density, where increasing 1,25(OH)₂D₃-glycoside increased bone density for the second rib (P = 0.012), but there was no treatment difference for other bones. There was no difference between treatments for antibody titers, 25(OH)D₃ status, or circulating cytokine concentrations except for IL-8 concentrations which decreased (linear, P = 0.037) as 1,25(OH)₂D₃-glycoside increased. In summary, adding 1.2 or 2.0 μg 1,25(OH)₂D₃-glycoside/kg provided from a plant extract to a diet already containing 1,653 IU/kg of vitamin D₃ had no effect on growth or the evaluated serum parameters; however, increasing 1,25(OH)₂D₃-glycoside increased percentage bone ash.