Skeletal health of layers across all housing systems and future research directions for Australia

Modern laying hens have been selected for an astounding rate of egg production, but the physiological calcium demand takes a significant toll on their skeletal health. Bones can be assessed both in vivo and ex vivo, using a combination of different structural and mechanical analysis methods. Typically, the properties of leg, wing and keel bones are measured. Conventional caged layers are restricted in movement, which imbalances structural bone resorption and new bone formation, resulting in osteoporosis. Hens within alternative housing systems have opportunities to exercise for strengthening bones, but they can also suffer from higher rates of keel fractures and/or deviations that are likely to have resulted from collisions or pressure force. Limited research has been conducted within Australian commercial housing systems to assess hen skeletal health, including prevalence of keel damage across different system types. Research conducted on both brown and white hen strains approximately within the past decade internationally (2009 onward) has shown that skeletal health is impaired across all housing systems. Keel-bone damage is of specific concern as it occurs at high rates, particularly in multi-tiered systems, is painful, can alter hen behaviour, and reduce both production and egg quality. Management strategies such as the provision of ramps to access perches and tiers can reduce the incidence of keel-bone damage to a degree. Bone strength can be improved through exercise opportunities, particularly when available during pullet rearing. Genetic selection for high bone strength may be necessary for hens to adequately adapt to loose-housed systems, but the best strategy for improving skeletal health is likely to be multifactorial.

The application of micro-CT in egg-laying hen bone analysis: introducing an automated bone separation algorithm

The application of micro-CT in small animal research, especially on bone health, has risen exponentially in recent years. However, its application in egg-laying hen bone analysis was still limited. This review introduces the technical aspects of micro-CT in egg-laying hen bone analysis, especially with the medullary bones presented in the cavity. In order to acquate application of micro-CT for laying hen bone research, image acquisition, reconstruction, and analysis settings need to be adjusted properly. The key difference regarding the application of micro-CT in laying hen bone compared to other small animals such as mice and rats was the larger bone size and more complex structures of medullary and trabecular bones. In order to analyze the details of laying hen bone structures, the volume of interest for laying hen should be selected at a region where all 3 bones are present (critical, trabecular, and medullary bone). Owing to the complexity of bone structures, the conventional techniques are not useful to distinguish the trabecular bone and medullary bone in laying hens accurately. In the current review, an automated segmentation algorithm is described to allow researchers to segment bone compartments without human bias. The algorithm is designed according to the morphology difference of medullary bones compared to trabecular and cortical bones. In this procedure, the loosely woven bones were separated by applying dual thresholds. The medullary calcium chunks were separated by opening or closing procedures, where we defined the diameter of medullary chunks being higher than the trabecular bone thickness as a separation trait. The application of micro-CT in laying hen bone health assessment will significantly expand our understanding of chicken bone physiology and osteoporosis, contributing to improve welfare in laying hens.

Gap between the fragment and the tibia affects the stability of tibial tubercle osteotomy: A finite element study

Tibial tubercle osteotomy (TTO) is commonly performed in cases of complicated juxta-articular trauma or revision total knee arthroplasty. However, strategies for firmly fixing the resulting osteotomy bone fragment are not sufficiently understood. This study aims to investigate the effect of the location of the gap between the fragment and the tibia and with various fixed screw configurations on TTO stability, contact force on the fragment, and bone stress by using the finite element method. A TTO model with a 1-mm gap, either above or below the fragment, was developed. Furthermore, five screw configurations, including two parallel horizontal screws placed at 20- and 30-mm intervals, two parallel downward screws, two trapezoid screws, and two divergent screws, were used. A vertically upward 1600-N force was applied on the tibial tubercle to mimic a worst-case condition. Placing the fragment close to the superior cutting plane (above the gap) yielded greater stability and less stress on the bone than did placing it close to the inferior cutting plane. The superior cutting plane of the tibia generated the largest contact force on the superior plane of the fragment for static balance under loading. Additionally, among all screw configurations, the configuration involving two parallel downward screws resulted in the highest stability but also the greatest stress on the cortical bone. The fragment obtains a solid barrier and support from the tibia immediately after surgery to against the patellar tension force when the fragment is close to the superior cutting plane of the tibia.