Ameliorative Effects of 25-Hydroxycholecalciferol Levels on Broiler Chickens Challenged with Infectious Bronchitis Coronavirus: A Novel Approach

ABSTRACT

SUMMARY This study aimed to see how 25-hydroxyvitamin D3 [25(OH)D] supplementation affected the performance, immunity, and vitamin D status of broilers, with and without infectious bronchitis virus challenge. Day-old chicks (n = 1000) were divided into four dietary treatments. All experimental treatments were containing 5000 IU of D3 and supplemented with 0, 100, 300, or 500 g/tonne of Bio D® containing 0, 13.94, 41.82 or 69.70 mg 25(OH)D, respectively. In unchallenged birds, the inclusion of 25(OH)D significantly improved survival rates and EPEF values, and no significant difference in LBW, BWG, FC, or FCR was observed. In infectious bronchitis virus (IBV)-challenged birds, the 25(OH)D treatment showed less deterioration in BWG, and FC compared with the control, especially 25(OH)D500 group. The lowest mortality was observed in the 25(OH)D500 group. The health status of chicks fed diets supplemented with 25(OH)D post-challenge had significantly better CD4, CD8, and immunoglobulin (IgG, IgM) levels, H/L ratio, total leucocytic count (TLC) in peripheral blood and IBV titers, cytokine (including interleukin (IL) 10) and (IFN)-γ expression, and reduced IBV shedding. After IBV challenge, all 25(OH)D groups recorded higher levels of plasma vitamin D than the control. Furthermore, 25(OH)D groups showed significantly higher antibody titers than the control group. In general, dietary supplementation with different levels of 25(OH)D had a positive effect on inflammatory reaction and stimulated the systemic innate immune responses of chickens during IBV challenge. In turn, recovery in the challenged birds with 25(OH)D rapidly occurred compared with that in the control group.