Table 1.

Study design.

Groups	Subgroups	Age at Challenge	Route of Challenge b	Number of Birds
Vaccinated a	V/a	20 DOA c	Intra-muscular	20
	V/b	20 DOA	Intra-nasal	20
	V/c	28 DOA	Intra-muscular	20
	V/d	28 DOA	Intra-nasal	20
	V/Nch d	-	-	12
Control	C/a	20 DOA	Intra-muscular	10
	C/b	20 DOA	Intra-nasal	10
	C/c	28 DOA	Intra-muscular	10
	C/d	28 DOA	Intra-nasal	10

^a Chicks were vaccinated with 1 dose of rHVT-ND vaccine on the day of hatch subcutaneously. ^b Chickens were challenged with a dose of 5.0 log₁₀ ELD₅₀ regardless the route. One subgroup of the vaccinated group was kept unchallenged until the termination of the second challenge. ^c DOA: days of age. ^d Nch: non challenged.