Life Sciences
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PRINCIPAL CONTACT:
Andrew A. Olkowski, PhD., DVM
[email protected]
306-966 5848
Biochemical and Physiological Weaknesses Associated with the Pathogenesis of Femoral Bone Degeneration in Broiler Chickens A.A. Olkowski (1), D. Chapman (2), T.W. Wysokinski (3), L. Quaroni (3,4), B. Laarveld (1), C. Wojnarowicz (5) (1) Department of Animal and Poultry Science, University of Saskatchewan (2) Department of Anatomy and Cell Biology, University of Saskatchewan (3) Canadian Light Source Inc. (4) Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland (5) Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan 38
Introduction Femoral bone degeneration is a common condition in commercial broiler chickens selected for rapid growth. From the commercial poultry industry perspective, this is a devastating disease of great economic importance with serious animal welfare implications.
degeneration based on findings from histo-pathology, biochemistry, microbiology, and synchrotron-based imaging techniques. In histo-pathological examination of advanced cases, changes in femoral bones are indicative of chondro- and osteonecrosis. The development of these lesions has been thought to be associated with bacterial infection. However, our studies questioned the initial involvement of bacteria. We discovered that the course of development of the lesions clearly points to the biochemical and patho-physiological changes in both organic and mineral matrices as the primary causes. Based on histological examinations, we observed that the changes in the mineralized matrix of the bone appear to be coupled with increased bone resorption associated with excessive proliferation of pathologically-altered osteoclasts. This is supported by the findings from computed tomography (CT) scans showing that the degenerative process involves the loss of trabecular bone (Figure 2).
The affected birds show characteristic clinical signs. When forced to move, they attempt to walk with the support of their wings. On overt clinical examinations, these chickens do not show any skeletal deformities. However, the association of clinical signs with femoral bone lesions can clearly be seen on post mortem examination (Figure 1).
Figure 1.
Science Etiological understanding of bone degeneration in chickens has historically focused on end point analyses of clinically advanced cases, with the approach to investigation mostly limited to microbiological and microscopic techniques. Our work presents more comprehensive analyses of the natural history of changes associated with femoral bone Canadian Light Source
Figure 2.
This evidence provides new insights into the pathogenesis of this condition. In this investigation a synchrotron-based imaging techniques generated information regarding the special distribution of structural changes in the inorganic matrix of the bone and a histological technique provided evidence on the possible underlying causes of these changes.
Research Highlights
Further analysis of light microscopy images suggested that the process of bone degeneration, in addition to the evident pathology of inorganic trabecular bone structures, may involve changes in the organic matrix of the bone. Therefore in order to further elucidate the etiology of bone degeneration we focused on changes in the organic matrix. We focused on bone proteins because the protein matrix provides major components for the proper development of the inorganic matrix. First, bones from normal and affected chickens were analysed using biochemical techniques to evaluate protein content. These analyses revealed that there are quantitative changes in the bone protein of birds showing degenerative lesions. FTIR was used to further examine the spatial distribution of these changes. Data from these studies are summarized in Figure 3.
The etiology of femoral bone degeneration has been investigated for some time, but many questions remain. Femoral head necrosis in broiler chickens was initially described as a condition associated with the bacterium Staphylococcus aureus, but some researchers questioned this tenet. We observed that bacterial infection is not the primary factor initiating the bone degeneration process. Our study provides new information that the pathogenesis of femoral bone degeneration may have a primary cause that is metabolic in nature. Inadequate synthesis and layout of extracellular matrix proteins in the rapidly developing bone may compromise the process of normal ossification and the resulting defective organic matrix may be unable to provide the proper nucleating and scaffolding sites for normal mineral propagation. In fast growing chickens, insufficiency of bone protein may result in the generation of “metabolically defective” bone tissue which is marked for pathological remodelling and eventual resorption, whereas insults, such as trauma, and eventually bacterial invasion, may simply be regarded as secondary complicating factors. 39
Conclusions
Figure 3.
From this study it is apparent that the affected birds show lower levels of bone protein, and this apparent deficiency should be considered a primary metabolic defect in the etiology of bone degeneration. It is also noteworthy that the biochemical analysis and the FTIR data provided similar results with regard to the basic changes in the composition of the organic matrix associated with bone degeneration. However, taken together, biochemical measurements and FTIR mapping provided more in-depth information regarding the differences in protein content and spatial distribution.
Discussion In recent years, the incidence of femoral bone degeneration in commercial chickens selected for rapid growth has been increasing at an alarming rate. The economic impact of this disease is obvious, but because of its debilitating course, the animal welfare implications of this condition are profound. Given this, finding a practical solution to this devastating condition is an urgent priority for the contemporary broiler chicken industry.
In this study we used several different techniques to gain detailed knowledge of the origins and progression of degenerative bone disease in chickens. Each of the techniques offered bits of essential and unique, but limited, information. Of note, CT scans, light microscopy, FTIR spectroscopy and biochemical analysis provided consistent evidence that femoral bone degeneration is associated with structural changes occurring in both the inorganic and organic matrices of the bone, but a deficiency in protein metabolism is most likely a primary etiological factor in the natural history of femoral bone degeneration. Taken together, the data gained from these studies provided a wealth of novel observations, which considerably advanced our understanding of the pathogenesis of this devastating condition.
References Principal publication: Olkowski AA, Laarveld B, Wojnarowicz C, Chirino-Trejo M, Chapman D, Wysokinski TW, Quaroni L. (2011) Biochemical and physiological weaknesses associated with the pathogenesis of femoral bone degeneration in broiler chickens. Avian Pathol. 40(6):639-50. DOI: 10.1080/03079457.2011.626017
Acknowledgements The research presented in this paper was supported by grants provided by the Poultry Industry Council and the Natural Sciences and Engineering Research Council of Canada. The authors also acknowledge the collaboration and generous support of Lilydale Inc.
2011 research Report
