Study of the efficacy and replication of recombinant vector vaccines using herpesvirus of turkey (rHVT) when combined with other Marek's disease vaccines

Several recombinant HVTs (rHVTs) have been developed within the last decades and they are commercially used worldwide. While in broiler chickens, rHVTs are usually administered alone, in long-living birds they are used in combination with Marek's disease (MD) vaccines of other serotypes (i.e. CVI988). The objectives of this work were (1) to evaluate protection against MD conferred by HVT and two rHVTs when combined with CVI988 and (2) to optimize the use of rHVT in combination with CVI988 to maximize replication of rHVT without compromising MD protection. Various vaccine protocols, all using rHVT or HVT at the recommended dose (RD), were evaluated. Protocols evaluated included in ovo vaccination with HVT+CVI988 or rHVT+CVI988 (using either double dose, DD, or the recommended dose, RD, of CVI988), day of age vaccination of rHVT+CVI988 at DD, and revaccination protocols using rHVT in ovo followed by CVI988 at DD at day of age. Our results show that, when combined with CVI988, HVT and rHVTs confer similar le...