Monitoring Marek’s disease (MD) vaccination is routinely done by evaluating load of MD vaccine in the feather pulp (FP) between 7-10 days of age. However, attempts in our laboratory to detect a novel CVI-LTR vaccine in the FP samples from commercial flocks failed. The objective of this study was to evaluate the most suitable tissue and age to monitor CVI-LTR vaccination. We used two different commercial CVI988 as controls. One hundred sixty one-day old commercial brown layers were vaccinated with either CVI-LTR, CVI988-A, CVI988-B, or remained unvaccinated. Samples of spleen, thymus, and bursa were collected at 3, 4, 5, and 6 days of age and samples of FP were collected at 7 and 21 days for DNA isolation. Our results showed that CVI-LTR replicated earlier than CVI988 vaccines in the lymphoid organs but was not detected in the FP either at 7 or at 21 days of age. We also confirmed that either spleen or thymus collected at 4-6 days was a suitable sample to monitor CVI-LTR vaccination in commercial flocks. Finally, we evaluated load of oncogenic MDV DNA in five commercial flocks that were either vaccinated with CVI-LTR + rHVT or with CVI988-A + rHVT. Load of oncogenic MDV DNA was evaluated at 21 days in the FP in 20 chickens per group. Our results demonstrated that CVI-LTR was more successful reducing oncogenic MDV DNA at 21 days of age than CVI988-A strain.