Association of increased rate of condemnation of broiler carcasses due to hepatic abnormalities with immunosuppressive diseases in the broiler chicken industry in Saskatchewan

Abstract

The objective of this study was to identify the causative agents of hepatitis observed in broiler chickens at processing. Livers of chickens from 16 broiler farms in Saskatchewan with gross lesions of hepatitis were collected at processing. In addition to routine bacterial isolation and histopathological examination, serologic studies for infectious bursal disease virus (IBDV) and Chicken anaemia virus (CAV), calculation of the ratio of the weight of the bursa of Fabricius (BF) to body weight (BBW), and histopathological examination of the BF were done. Of the 264 livers with gross lesions, 83% had multifocal to coalescing necrotizing hepatitis, 16% had perihepatitis, and 1% had hemorrhages. No definitive causative microorganisms were isolated from the hepatic lesions; however, no significant bacterial isolations were made. Bursal atrophy, low BBW ratio, and high titer of antibody against IBDV each correlated with the rate of total condemnations (P = 0.0188, P = 0.0001, and P = 0.0073, respectively). Nucleotide sequencing of IBDV isolated from the BF identified the variant strains Delaware-E and 586. Condemnation because of hepatic lesions was correlated with titer of antibody against IBDV and BBW (P = 0.016 and P = 0.027). The results of this study demonstrate that hepatic lesions in Saskatchewan chickens are not currently caused by a primary bacterial pathogen but are associated with indicators of immunosuppression that is likely due to variant IBDV.

Figure 1

Histopathological appearance of bursa of Fabricius (BF). A — normal follicles. B — mild bursal atrophy: atrophy of some follicles. C — moderate bursal atrophy: small lymphoid follicles and prominent interfollicular architecture. D — severe bursal atrophy: severe, diffuse loss of follicles. E — severe bursal atrophy: widespread depletion of lymphocytes in follicles. F — severe bursal atrophy: prominent follicular epithelium. Hematoxylin and eosin (H&E) staining. A to D — original magnification × 2. E and F — original magnification × 10.

Figure 2

Macroscopic and microscopic appearance of livers condemned at processing. A — mild acute hepatitis, with multifocal yellowish to white necrotic areas 2 to 4 mm in diameter. B — subacute moderate hepatitis, with multifocal to locally extensive spots of the same size. C — severe chronic hepatitis, with locally extensive to diffuse spots of the same size. D — locally extensive moderate to severe chronic perihepatitis. E — multifocal necrotic centers of C; original magnification × 4. F — higher magnification of E; necrotic focus containing cell debris surrounded by macrophages and giant cells, with expansion of extramedullary granulopoiesis (arrow); original magnification × 10. G — higher magnification of an area with expansion of extramedullary granulopoiesis in a liver with hepatitis; original magnification × 40. H — higher magnification of an area with expansion of extramedullary granulopoiesis in a liver with perihepatitis; original magnification × 40. H&E staining.