Comparative safety study was conducted over a period of 42 days following vaccination of SPF and commercial chickens with 3 commercially available ND vaccines : one pneumotropic strain, Vaccine A (NobilisClone30) and two reputed enterotropic strains, Vaccine B (Avinew) and Vaccine C (Cevac VitapestL). One dose of vaccine was administered by eye drop to 50 day-old chicks. Assessment criteria were : growth performance over 6 weeks post-vaccination (p.v.), presence of respiratory reactions for 2 weeks p.v. and histologic examinations of liver, pancreas and trachea on days 7, 14, 21, 28, and 42 p.v..

With regard to the weight of the body, no significant difference was observed between the control and vaccinated groups, in SPF and commercial birds. No clear post-vaccine respiratory reaction was audible whatever the vaccine group. Regarding the liver, no significant lesion was detected in any of the samples examined. Very few SPF vaccinated birds shown a severe lymphoïd infiltration (l.i.) in the pancreas : 1/50 (vaccine A), 3/50 (Vaccine B). No lesion in the pancreas was detected in control birds or in vaccinated birds with Vaccine C.

In SPF birds, no tracheal lesion was observed in birds that were either control or vaccinated with Vaccine C. Moderate to pronounced l.i. were detected in vaccinated birds with Vaccine A from 7 days (5/10 birds) up to 42 days (2/10 birds). Likewise, in birds vaccinated with Vaccine B, it was observed moderate to pronounced l.i. at 28 days p.v. (9/10) and still moderate l.i. at 42 days p.v. (4/10). This probably was due to a late colonisation of the trachea by the Vaccine B.

In commercial birds, moderate l.i. was detected in non‑vaccinated birds from 21 days up to 42 days p.v. This probably was a consequence of potential saprophytic bacteria carriers. Lesions equivalent to those observed in non-vaccinated chickens were detected in birds vaccinated with Vaccine C. Moderate l.i. was detected in 2 to 10/10 vaccinated birds with Vaccine A, from 7 days up to 42 days p.v.. Pronounced l.i. was observed in group which receive Vaccine B from 14 days up to 42 days p.v. (2/10 birds); at 21 days p.v. 8/10 birds were concerned.

It can be concluded that Vaccine C has no tropism for trachea unlike Vaccines A and B. It doesn't impaired the bird growth and doesn't present adverse effect on pancreas.

Published in the XXIth World Veterinary Poultry Association CONGRESS – 28th Jan –1st Feb 2002