Aspects of bone quality in the broiler chicken
The work contained in this thesis explores the development of the tibiotarsus shaft and the quality of cortical bone in the modern broiler, in relation to genetic background, growth rate and dietary mineral content. This was achieved through a series of experiments predominantly using a modern selected strain of broiler and an older, unselected control strain, and occasionally utilising current commercial stock. Birds were exposed to a variety of dietary mineral contents, and feeding regimes, and assessments were made of a number of aspects of bone quality, bone turnover, and mineral homeostasis at selected ages .A number of phases in tibiotarsus development were identified from the embryo through to slaughter age at approximately six weeks; these were seen in all strains of broiler chicken investigated. Resorption and replacement of the embryonic cartilage model of the tibiotarsus was found to begin before day 16 of incubation, and a reduction in cortical thickness was observed between this age and hatch as the marrow cavity was enlarged. During this period, the cortex was observed to develop from a maze like scaffold, to display recognisable Haversian canals with the new bone being rapidly mineralised; by day 6, the cortex displayed a distinctive pattern of Haversian canals which remained consistent throughout much of the bird's life-span. From hatch, cortical width began a rapid increase in thickness, which was seen to halt at approximately 18 days of age, cortical thickness remaining approximately constant from this age. The rapid increase in cortical mineral content was also seen to plateau at approximately 11 days.