Dissertation

Influence of growth rate on the immature skeleton

Murray, Dianne Hamilton

2005

Overview

To investigate how bone architecture is modulated by growth rate, morphometric, biochemical and genetic comparisons were made between tibiae from broiler chickens with either fast or slow growth potentials. Both strains of chickens were kept under identical conditions, and fed ad-libitum standard broiler feed. Tibiae were removed and tested by three-point bending to determine stiffness and breaking strength and cross sections of the tibia were examined histomorphologically. Bone stiffness and breaking strength were higher in the rapidly growing birds, but after adjustment for body weight the bones were inherently weaker. Cortical porosity periosteally, but not endosteally, was increased. Sections reacted for ALP and TRAP activity, and others stained for cement (reversal) lines indicated the absence of primary osteon remodelling in the periosteal region. This suggests that the increased periosteal porosity is due to slower infilling of the primary osteons in the rapidly growing birds. To directly quantify the rate of osteon infilling, tibiae were removed from 21-day-old chicks, which had been double labelled with calcein (80 and 8 h before death). The mineral apposition rate was higher in the slow growing chickens, and confirmed the previous histomorphometry results. Osteocyte density within the circumferential lamellae of the cortical bone was higher in the rapidly growing birds but unchanged within the newly laid down bone of the primary osteons. Immunohistochemical staining of cortical bone sections from chickens injected with bromodeoxyuridine located proliferating pre-osteoblast cells to the osteogenic layer of the periosteum. A lower labelling index in the rapidly growing birds was seen across four circumferential areas of the periosteum (anterior = fast growing area, posterior = slow growing area, medial and lateral = intermediate growing areas), even though the osteogenic layer of the periosteum was thicker in the fast strain. Blood vessel numbers within the periosteum was similar between strains but differed between regions habitually loaded in tension (anterior) or in compression (posterior).

• Publisher: ProQuest Dissertations & Theses
• Subject: Animal Diseases