Influences the Marek's disease vaccine (MDV) alone or combined with the in ovo and dietary administration of 25-hydroxycholecalciferol (25OHD3) on the expression of genes associated with the breast muscle deposition, adaptive and innate immunity, and antioxidant and vitamin D activities of 14 d-old broilers were investigated. Four in ovo treatments were: non-injected; commercial MDV-alone-injected (50 μl); or 50 μl of MDV containing 1.2 (MDV+25OHD3-1.2) or 2.4 (MDV+25OHD3-2.4) μg of 25OHD3. Two dietary treatments were a commercial diet containing 25OHD3 (250 IU)/kg of feed (control) or the same diet supplemented with additional 25OHD3 (2,760 IU)/kg of feed (Hy-D diet). One bird per pen (48 total) was sampled at 14 d for determination of the expression of genes involved with the muscle deposition (MyoD1, MyoG, Pax3, and Mrf4), immunity (INF-γ, IL-10, IL-8, IL-1β, and TGF-β4), antioxidant capacity (SOD1, SOD2, GSH-P1, GSH-P7, and CAT), and vitamin D activity (VDR, 1α-hydroxylase, and 24-hydroxylase) in the spleen and pectoralis major (P.major) muscle. The treatment differences were considered significant at P ≤ 0.05. In the P. major, Mrf4 and MyoG were up-regulated in Hy-D-fed birds. Also, the in ovo and dietary 25OHD3 sources individually increased SOD2 gene expression in the P. major. In the spleen, the expressions of IL-1β and IL-8 were down-regulated and IL-10 and TGF-β4 gene expressions were up-regulated in Hy-D-fed birds than those commercial-fed broiler. In ovo and dietary 25OHD3 sources enhanced vitamin D gene (1α-hydroxylase and 24-hydroxylase) activities in the breast and spleen. In ovo x dietary treatment interactions were significant for the MyoD1, IL-8, Pax3, TGF-β4 genes of the P. major, in which the combined MDV with 1.2 μg of 25OHD3 enhanced their expressions in birds fed the Hy-D diet. In conclusion, both 25OHD3 sources promoted the expression of genes associated with immunity and P. major growth. It is recommended that both 25OHD3 sources can be used to promote the gene expression of 14-d-old broilers in the spleen and breast muscle when MDV administered in ovo.
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