Bone fragility in egg laying hens

骨是一种常见且普遍存在的组织，形成大多数脊椎动物的骨骼，然而几乎所有关于骨适应性和脆弱性的已知信息都是从哺乳动物的研究中收集的。产蛋母鸡是所有脊椎动物中最有效的钙转运体，每天将其体内约10%的钙转移到蛋壳中，估计其中只有一半来自饮食来源。据估计，20-35%的死亡发生在商业笼养蛋鸡是由潜在的废用性骨质疏松症。值得关注的是龙骨骨折的患病率，据报道，5.5%的母鸡在产蛋开始时发生龙骨骨折，到产蛋结束时影响高达97%的母鸡。加拿大最近禁止建造新的传统笼舍，并规定20年内逐步采用替代住房。很少有人知道替代住房对骨量，结构，特别是组织水平的材料性能在不同品系的鸡的影响。有趣的是，研究表明，与传统笼舍中的母鸡相比，自由运行的地板饲养或禽舍系统中的母鸡具有更强的骨骼，但更高数量的陈旧性愈合骨折（发生在人口减少之前）。这些骨折的病因尚不清楚，尽管有人推测是由于碰撞增加所致。目前尚不清楚骨骼对不同外壳提供的机械刺激的适应性如何导致骨折风险。 在这项研究计划中，我将检查母鸡圈养在三个常用的商业可用的系统，提供不同程度的机械刺激。我将研究在两个品系的母鸡（罗曼布朗和罗曼选择莱霍恩-建兴）在整个产蛋期（18，32和54周龄）的各种活动中在龙骨中产生的机械应变。我还将检查骨折和非骨折的龙骨骨质量，微观结构和质量在母鸡，以确定是否结果的措施在骨折改变。为了确定骨折过程中的骨质是否也会在远端部位恶化，我还将在有和没有龙骨骨折的成年母鸡的长骨（胫骨）中进行这些分析。本NSERC DG的短期目标是阐明母鸡龙骨骨折的病因。我的计划的长期目标是使用生物工程方法来了解鸟类的骨骼健康。该计划将使我们能够在高度受控的动物模型和环境中研究在骨骼调节和适应中发挥关键作用的两个基本过程之间的详细相互作用-机械刺激和矿物质稳态。这项研究计划准备为加拿大家禽养殖户提供有关龙骨骨折病因的信息，以及住房环境如何可能导致骨折风险，因为他们寻求遵守新的住房指南。

Bone is a common and ubiquitous tissue that forms the skeletons of most vertebrates, however nearly all of what is known concerning bone adaptation and fragility has been gleaned from studies in mammals. The egg laying hen is the most efficient calcium transporter among all vertebrates, transferring approximately 10% of its total body calcium volume daily to produce an egg shell, of which only half is estimated to originate from dietary sources. Estimates suggest that 20-35% of mortalities occurring in commercially caged egg-laying hens are caused by underlying disuse osteoporosis. Of concern is the prevalence of keel bone fractures that are reported to occur in 5.5% of hens at the onset of lay and affect up to 97% of hens by the end of lay. Canada has recently implemented a ban on new conventional cage construction and a 20-year phase-in period of alternative housing. Little is known about the effect of alternative housing on bone mass, structure and especially tissue level material properties in different strains chickens. Interestingly, studies have shown that hens in free run floor-housed or aviary systems have stronger bones, but a higher number of old healed fractures (occur prior to depopulation) compared to hens housed in conventional cages. The etiology of these fractures remains unclear, although some speculate that they are due to increased collisions. It remains unclear how bone adaptation to mechanical stimuli provided by different housing contributes to fracture risk. In this research program, I will examined hens housed in three commonly used commercially available systems which provide varying levels of mechanical stimuli. I will examine mechanical strains engendered in keel bones during various activities in two strains of hens (Lohmann Brown and Lohmann Select Leghorn-Lite) throughout the lay period (18, 32 and 54 weeks of age). I will also examine fractured and nonfractured keel bone mass, microstructure, and quality in hens to determine if outcome measures are altered in fractured bones. To determine if bone quality during fracture is also deteriorated at remote sites I will also perform these analyses in a long bone (tibiotarsus) of adult hens with and without keel bone fractures. The short-term goal of this NSERC DG is to elucidate the etiology of keel bone fractures in hens. The long-term goal of my program is to use bioengineering approaches to understand skeletal health of birds. This program will allow us to study in a highly-controlled animal model and environment, the detailed interactions between the two fundamental processes that play critical roles in bone regulation and adaptation - mechanical stimulation and mineral homeostasis. This research program is poised to provide Canadian poultry farmers information concerning the etiology of keel bone fractures and how housing environments may contribute to fracture risk, as they seek to adhere to new housing guidelines.