Immunizing characteristics of a tissue-culture-origin modified live-virus ocular vaccine for infectious laryngotracheitis.

Abstract

The minimum protective dose of a tissue-culture-origin (TCO) modified laryngotracheitis (MLT) ocular vaccine was determined in 4and 12-week-old White Rock broiler-type chickens. Vaccine seed stocks, prepared from different passage levels at widely differing points of time, were tested also. Data showed that the minimum protective dose for this vaccine is approximately 103.0 EID50/ml. Route of challenge (intratracheal vs. intrasinus), age of birds at vaccination, and housing conditions (cage vs. floor) had little effect on the outcome of these tests. Results of testing virus seed stocks confirmed the data obtained on commercial vaccine and also showed that the antigenic qualities of the virus are very stable.