RESUMEN
The susceptibility of three F1 hybrid lines of chickens to graded doses of infectious laryngotracheitis virus (ILTV) was investigated. The three F1 hybrid lines, each produced from mating two inbred lines, included the SC (B2B2) and TK (B15B21) lines and the 15I5 x 7(1) (B2B15) line. Although at 1 d of age all three lines were susceptible to ILTV, SC birds were significantly less susceptible (10%) than TK (80%) or 15I5 x 7(1) (50%) birds when exposed to 5,000 pfu of virus at 4 wk of age. The ability of each inbred F1 hybrid line to establish a protective immune response to ILTV was also determined. The SC birds required a smaller immunizing dose of virus (500 pfu) to mount a protective immune response to ILTV than the 15I5 x 7(1) line (5,000 pfu). A 5,000 pfu immunizing dose did not elicit a protective immune response in the TK line to a 10(6) pfu challenge dose of ILTV. These results also correlated with the ability to produce ILTV-specific antibodies. This study confirms and expands on observations that lines of chickens differ with respect to their susceptibility and resistance to ILTV.