Avian articular cartilage: effects of age, genotype and disease
Anderson-MacKenzie, Janet Melanie
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The degradation of articular cartilage, causing degenerative joint disease (DJD), is a documented cause of lameness in broiler strain fowl, which is a major welfare problem. Broiler strain fowl are both heavier and more susceptible to DJD than laying strain fowl. In this thesis the biochemical and morphological basis for this susceptibility has been investigated, particular attention has been paid to the effects of body weight and genotype on avian articular cartilageArticular cartilage from three distinct sites was analysed. Samples from mature broiler strain females, susceptible to DJD, had higher hydration and uronic acid content than age matched, non -susceptible, laying strain fowl. In addition to these biochemical features (also seen in mammalian DJD), broiler strain fowl exhibited DJD histopathology including cartilage thinning and chondrocyte cluster formation. In general, both strains at one day old showed no significant biochemical differences between the articular cartilage sites sampled. However the cartilage from the broiler strain distal tibiotarsus (DTT) at one day old appeared to be biochemically and morphologically distinct from the cartilage of the layer strain DTT and from the other broiler strain joint surface of the same age.Production of an infectious arthritis by inoculation of mycoplasma into the tibiotarsal joint of broiler strain fowl resulted in variable biochemistry of articular cartilage form this joint. However in the non -injected, contralateral joint, sampled from the DTT, there was an increase in hydration and uronic acid content which is dependent upon the degree of lameness. This indicates the importance of in vivo loading in the biochemical composition of avian articular cartilage.Broiler strain birds fed ad libitum, feed restricted and J -line (wild type) were surveyed over the course of one year. Only the ad libitum fed birds developed overt DJD, which suggests that the mass of the bird, and not an overriding genetic element, is the major cause of the susceptibility of broiler strain fowl to DJD. The joint surface which presented the first and most severe signs indicative of early cartilage degeneration was the DTT. The biochemical results obtained from articular cartilage samples of the three groups include hydration, uronic acid, DNA and hydroxyproline content. Histology of the samples was assessed using haematoxylin and eosin stained sections. Proteoglycan content was investigated further by using selected samples for sulphated glycosaminoglycan assays and staining selected sections with Toludine blue and Safranin O. Samples from diseased and non -diseased groups were assayed for pyridinium in order to investigate the role of mature collagen crosslinking in DJD.The exact role of load and the metabolic consequences of body weight in the development of DJD is controversial. A method for artificially loading non -obese birds has been developed. Loading feed restricted broiler strain fowl with an additional 10% of their body weight over a three week period initiated a response including significant biochemical changes in the cartilage of the DTT. These results again emphasise the importance of load on the articular cartilage and the susceptibility of the DTT to DJD.