Effects of <i>in ovo</i> injection of 25(OH)D ₃ in combination with Marek’s disease vaccine on hatchability, performance and bone health of broilers

1. This study assessed the effects of <i>in ovo</i> injection of Marek's disease vaccine (MDV), alone (control) or combined with 1.25 μg of 25-hydroxycholecalciferol (25(OH)D₃), on hatchability, chick quality, performance and bone quality in Cobb 500 broilers. At d 19 of embryo development, eggs were injected with 0.05 ml of MDV or MDV plus 1.25 μg of 25(OH)D₃ into the amniotic fluid following hatchery protocol. Post-hatch, 840, one-day-old male chicks were reared until d 35 of age.2. Hatchability and general chick quality were not affected by the treatments. However, the male chicks that received MDV + 1.25 μg of 25(OH)D₃ presented longer length at flock thinning compared to those that received only MDV. At 35 d of age, broiler performance, gait score and leg deformities (valgus and varus) were not affected.3. Although chicks receiving the MDV + 1.25 μg of 25(OH)D₃ had lower macroscopic tibial dyschondroplasia (TD) scores at 7 d of age compared to those given MDV, this difference was not sustained as they matured. Tibia weight, thickness and length were similar across treatments at all time points. However, the tibiae from chicks in the MDV + 1.25 μg 25(OH)D₃ group demonstrated greater strength on d 1 and 7 but not at later times.4. In conclusion, this study showed that combining 25(OH)D₃ with MDV does not impact hatchability or overall performance but does enhance early bone strength and growth in broiler chicks.