What vaccination programs are recommended for commercial broiler and layer flocks?

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Commercial broiler flocks are routinely vaccinated against Marek's disease (MD), Newcastle disease (ND), infectious bronchitis (IB), infectious bursal disease (IBD/Gumboro disease), and coccidiosis, with program selection driven by regional circulating strains, production type, and route of administration. For broilers, in ovo vaccination is the dominant delivery platform for MD. The herpes virus of turkey (HVT) vaccine was the first vaccine successfully administered in ovo, and the majority of commercial broilers in the United States transitioned from subcutaneous HVT administration to in ovo vaccination over a span of 20 years.11 Commercially, in ovo vaccines are now employed against MD, IBD, infectious laryngotracheitis (ILT), poxvirus, ND, avian influenza, and coccidiosis.11 IBD vaccination programs for broilers include classical live vaccines, live HVT-IBD vector vaccines, and the Vaxxitek HVT+IBD recombinant product. Broilers vaccinated with Vaxxitek HVT+IBD show higher body weight at slaughter and lower feed conversion ratio and mortality compared to other IBD vaccine programs, though statistically significant differences were confirmed only for the European Poultry Efficiency Factor.1 Broilers vaccinated with an HVT-IBD vector vaccine against IB show increased average daily body weight gain of +1.13 g and lower feed conversion ratio of −0.05 compared to birds on classical live IBD vaccine programs.1 For ND in broilers, the standard Israeli protocol — representative of intensive commercial programs — consists of a live vaccine by spray on the day of hatching, an inactivated vaccine by subcutaneous injection at 10–12 days of age, and a second live vaccine by aerosol at 17–21 days of age. At the peak of induced immunization at week 5, 87.5% of tested flocks achieved herd immunity, defined as ≥85% of birds with a hemagglutination inhibition titer ≥4.13 Flocks without herd immunity carry an odds ratio of 3.7 for ND outbreak.13 Classical genotype I and II vaccine