Risks and disease aetiologies of compromised performance in commercial broilers kept at lower stocking density and limited antimicrobial use.

The health status of broilers raised at lower stocking density and limited antimicrobial use (but routine anticoccidials) was assessed in order to identify prevalent causes of disease, mortality and reduced performance. "Dead-on-farm"(DOF) broilers from 145 commercial flocks were investigated at two different time points (TP1:7-14 and TP2:28-35 days of age); per sampling, 6-10 DOF broilers were selected for post-mortem investigation and gross pathomorphological changes were assessed from 2717 birds in total. Post-mortem findings were substantiated by bacteriological, virological and parasitological investigations. Furthermore, production data of all flocks were collected and used to perform comprehensive statistical analysis. Overall, colibacillosis was found most important with a significant negative impact on flock health, productivity and profitability through all ages of broiler production. At TP1, primary reasons for mortality comprised yolk sac infections, generally found together with fibrinous polyserositis due to E. coli. Furthermore, femoral lesions, which correlated with increased flock mortality, were associated with detection of E. coli. At TP2, ascites was detected frequently in DOF broilers, correlating with increased production losses in the fourth and fifth weeks of life. No aetiological link between the presence of ascites and the detection of the investigated pathogens was observed, instead a positive correlation was noticed with altitude above sea level of the farm, and with the sex of the birds. Disease conditions could not be linked with the housing system. Presence of infectious bronchitis virus, avian reovirus and fowl adenovirus did not correlate with macroscopic lesions or a specific disease. RESEARCH HIGHLIGHTS In young broilers lesions of visceral organs due to bacterial infections dominated. Colibacillosis impacts broiler health, productivity and profitability independent of the age of birds. Disorders of the locomotor system were frequently observed throughout production. Older broilers frequently showed pathologic changes due to metabolic disorders. Overall, a shift from infectious towards metabolic disease conditions was noticed.

Escherichia coli isolates from femoral bone marrow of broilers exhibit diverse pheno- and genotypic characteristics that do not correlate with macroscopic lesions of bacterial chondronecrosis with osteomyelitis.

The pheno- and genotypic relatedness among Escherichia coli isolates from broilers with and without macroscopic lesions of the femoral head were investigated. In total, 219 isolates obtained from the bone marrow were characterized by serotyping, antimicrobial resistance (AMR) profiles, phylogenetic grouping, detection of virulence-associated genes (VAGs) and pulsed-field gel electrophoresis (PFGE). Serotyping revealed that 48.4% of the isolates were assigned to one of the three serotypes (O78:K80: 21.0%, O2:K1: 18.7%, O1:K1: 8.7%). Substantial phenotypic variation was also noticed in AMR testing as most of the birds harboured E. coli isolates with different AMR profiles, which is of high clinical relevance. The majority of isolates could be classified into phylogenetic groups D (54.3%) and B2 (25.6%), followed by A (11.4%) and B1 (8.7%). Virulotyping showed that the highest number of isolates contained genes iucD (86.8%) and iss (84.9%), whereas papC (16.0%) and astA (12.3%) were present in least number of isolates. PFGE resulted in 58 different profiles from 200 typeable isolates. No correlation was found between specific serotypes, AMR profiles, phylogenetic groups, PFGE types or VAG profiles of E. coli and the occurrence of bacterial chondronecrosis with osteomyelitis, contradicting the hypothesis of a specific bacterial pheno- or genotype being involved in the disease.