The combined effects of the in ovo injection of commercial Marek's disease vaccine (MDV) and various levels of 25-hydroxyvitamin D₃ (25OHD₃) on the hatch variables, immunological measurements, and gene expression of Ross 708 hatchling broilers were investigated. A total of 5 in ovo injection treatments that were applied at 18 d of incubation (doi) included: 1) noninjected (control); or a 50 μL solution volume of 2) MDV alone; or MDV combined with 3) 0.6 μg of 25OHD₃; 4) 1.2 μg of 25OHD₃; or 5) 2.4 μg of 25OHD₃. At hatch, hatchability of set and live embryonated eggs, hatchling body weight, hatch residue analysis, serum IgY and alpha-1 acid glycoprotein (AGP) concentrations, and the expression of genes related to immunity (INFα, INFβ, INFγ, TLR-3, and TLR-21) and vitamin D₃ activity (1 α-hydroxylase, 24 hydroxylase, and vitamin D receptor) were determined. No significant treatment differences were observed for hatchability of set and live embryonated eggs, or for serum IgY and AGP concentrations. However, hatchling body weight was higher when MDV was combined with either 1.2 or 2.4 μg of 25OHD₃ than when MDV was provided alone or in combination with 0.6 μg of 25OHD₃. Also, in comparison to the noninjected treatment group, the expression of the genes for 1 α-hydroxylase and 24 hydroxylase was improved when MDV was combined with either 1.2 or 2.4 μg of 25OHD₃. Lastly, expression of the genes linked to viral detection (TLR-3) and antibody production (INF-β) was increased in those treatments that contained any level of 25OHD₃. These results indicate that in comparison to controls, the effects of MDV were observed to be greater on hatchling BW and splenic gene expression when it was administered in combination with the 1.2 or 2.4 μg doses of 25OHD₃. Further research is needed to determine the posthatch effects of the administration of various levels of 25OHD₃ in combination with MDV.

The effects of the Marek’s disease vaccine (MDV) on the live performance, breast meat yield, and incidence of woody breast myopathy (WBM) of Ross 708 broilers were investigated when administered alone or in conjunction with in ovo and dietary supplemental 25-hydroxycholecalciferol (25OHD₃). At 18 d of incubation (doi), four in ovo injection treatments were randomly assigned to live embryonated Ross 708 broiler hatching eggs: (1) non-injected; (2) commercial MDV alone; or MDV containing either (3) 1.2 or (4) 2.4 μg of 25OHD₃. An Inovoject multi-egg injector was used to inject a 50 μL solution volume into each egg. The birds were provided a commercial diet that contained 250 IU of cholecalciferol/kg of feed (control) or a commercial diet that was supplemented with an additional 2760 IU of 25OHD₃/kg of feed (HyD-diet). In the growout period, 14 male broilers were placed in each of 48 floor pens resulting 6 replicated pens per in ovo x dietary treatment combination. Live performance variable were measured at each dietary phases from 0 to 14, 15 to 28, and 29 to 40 d of age (doa). At 14 and 40 doa, pectoralis major (P. major) and pectoralis minor (P. minor) muscles were determined for one bird within each of the six replicate pens. At 41 doa, WBM incidence was determined. No significant main or interaction effects occurred for WBM among the dietary or in ovo injection treatments. However, in response to in ovo 25OHD₃ supplementation, BW and BWG in the 29 to 40 doa period and BWG and FCR in the 0 to 40 doa period improved. In addition, at 40 and 41 doa, breast meat yield increased in response to in ovo and dietary 25OHD₃ supplementation. Future research is needed to determine the possible reasons that may have been involved in the aforementioned improvements.

In ovo injection of the Marek’s disease (MD) vaccine (MDV) has been widely practiced in commercial US hatcheries. However, the MDV is very sensitive and may not be compatible with some nutrients when administered together by in ovo injection. When individually administered by in ovo injection, L-Ascorbic acid (L-AA) and 25-hydroxyvitamin D₃ (25OHD₃) have previously exhibited very promising results on the post-hatch physiological and immunological characteristics of broilers subjected to stressful commercial conditions. However, the compatibility of the MDV with these vitamins has not been previously explored. Their compatibility must first be established before their combined administration by in ovo injection can be considered. Therefore, the objective in this study was to determine the compatibility of the MDV with various levels of 25OHD₃ or L-AA. The treatments employed were MDV-alone, MDV in combination with 0.6 (low) or 2.4 (high) μg doses of 25OHD₃, or MDV in combination with 1.2 (low) or 12 (high) mg doses of L-AA. The live and dead ratio of primary chick embryo fibroblast cells infected by the MD virus (CEF-MDV) in each treatment was determined every 30 min for 2 h. The L-AA at both the low and high doses resulted in a 70% death of CEF-MDV within 1 h, but either dose of the 25OHD₃ exhibited only an approximate 5% lower CEF-MDV survival as compared to those in the MDV-alone treatment. Therefore, it is suggested that the two designated doses of 25OHD₃ have the potential to be effectively combined with the MDV for subsequent administration by in ovo injection.