Applied research note: Development of an Avian Pathogenic Escherichia coli infection model in layer chickens

Development of novel means of control for Avian Pathogenic Escherichia coli (APEC) is dependent upon robust disease models. While a few APEC models have been described in the literature for mature laying hens, there is a lack of models describing APEC infection in younger birds. We describe here two studies focused on the development of an APEC airsacculitis disease model in young pullets and pre-lay hens. In the first study, four-week-old cockerels were inoculated with one of four APEC strains at one of four doses (0, 1 × 10², 1 × 10⁴, and 1 × 10⁶ CFU/mL) and evaluated for signs of airsacculitis via post-mortem gross lesion scoring for 10 days post-inoculation. Airsacculitis scores demonstrated a difference in disease timing and incidence by strain and dose within strain. However, the majority of airsacculitis lesions were only a score of 1 demonstrating low disease severity and a potential resistance of young birds to APEC infection. In the second study, 18-week-old hens previously vaccinated against Mycoplasma gallisepticum were inoculated with a virulent APEC strain. Evaluation of airsacculitis scores at 2-, 5-, and 7-days post-inoculation revealed a consistent increase in airsacculitis incidence. While further studies are needed to fully validate and characterize these models, the current results provide valuable information on the additional needs for developing an APEC model in pullets and the potential of Mycoplasma gallisepticum vaccination with APEC infection to be a promising disease model for in pre-lay hens.