Ross 708 broiler small intestine morphology and immunity improvements in response to in ovo Marek's Disease vaccine administration alone or in conjunction with in ovo and dietary supplemental calcifediol.

Investigations were performed to determine the systemic immune and small intestine (SI) morphological responses of Ross 708 broilers to the Marek's Disease vaccine (MDV) administered alone or in conjunction with the in ovo and dietary administration of calcifediol (25OHD). Live embryonated hatching eggs were assigned at random to 3 in ovo treatments at 18 d of incubation. Pre-specified in ovo treatments were: commercial MDV-alone-injected (50 µL) or commercial MDV containing 1.2 (MDV+25OHD-1.2) or 2.4 (MDV+25OHD-2.4) μg of 25OHD. A noninjected control treatment was also included. For the growing phase, broilers received a commercial diet containing 250 IU of vitamin D /kg (control) or a commercial diet supplemented with 2,760 IU of 25OHD /kg (Hy-D diet). For determination of serum IgG, nitric oxide, and α-1-acid glycoprotein (AGP) at 14 and 40 d of age (doa), blood was collected from 1 bird per pen (48 total). In the duodenum, jejunum, and ileum of the same bird, villus length (VL), crypt depth (CD), VL to CD ratio (VCR), and villus surface area were also determined. There were no significant dietary x in ovo treatment interactions for any of the variables examined. However, birds fed Hy-D diets had lower serum AGP levels at 14 doa when compared to those fed un-supplemented commercial diets. Additionally, at 40 doa, birds in the MDV+25OHD-1.2 and MDV+25OHD-2.4 treatments experienced a decrease in serum AGP in comparison to those belonging to the noninjected and MDV-alone treatment groups. A higher jejunal VCR was observed at 14 and 40 doa in birds that belonged to the MDV+25OHD-1.2 treatment when compared to those in the noninjected and MDV-alone treatment groups, and dietary Hy-D increased the VL of the duodenum and jejunum in birds at 14 and 40 doa when compared to those fed the commercial diet. In conclusion, both dietary or in ovo administration of 25OHD lowered inflammatory reactions and improved the SI morphology of broilers that were in ovo-injected with the MDV.