Antibody response against newcastle disease in commercial broilers fed different dietary protein levels

A factorial experiment was conducted with two levels of dietary protein (17.5 and 26%) and three vaccination regimens (inactivated oil-emulsion, live LaSota strain, and unvaccinated) against Newcastle disease at 10 days of age. There were two trials with 3 pens of 15 male broiler chicks each per cell. Birds fed the high protein diet grew significantly better (P less than .05) in the second trial (1731 g at 6 weeks vs. 1622 g) but not in the first (1304 vs. 1244 g); no growth differences were noted due to vaccine. At 3 weeks of age, the hemagglutination-inhibition antibody titers from the live vaccine were significantly (P less than .01) higher than from the inactivated vaccine. At 3 weeks of age, antibody titers from the inactivated vaccine were elevated (P less than .05) in birds fed the low protein diet in the second trial. At 6 weeks of age, antibody titers were affected by vaccine (P less than .05) but not by dietary protein. Antibody titer levels were higher from the inactivated vaccine than from the live vaccine in the first trial; these results were reversed in the second trial. Postchallenge results with the Texas GB strain of Newcastle did not reveal any significant differences due to dietary protein content, trial, or type of vaccine.