Bone fragility in egg laying hens

骨骼是构成大多数脊椎动物骨骼的一种常见和普遍的组织，然而几乎所有关于骨骼适应和脆性的已知信息都是从哺乳动物的研究中收集的。蛋鸡是所有脊椎动物中最有效的钙转运体，每天转移大约10%的全身钙来产生蛋壳，据估计只有一半来自饮食来源。据估计，在商业笼养的蛋鸡中，20%-35%的死亡是由潜在的废用性骨质疏松症引起的。令人担忧的是龙骨骨折的流行，据报道，龙骨骨折在产蛋初期发生在5.5%的母鸡，并在产蛋结束时影响高达97%的母鸡。加拿大最近实施了一项禁令，禁止建造新的传统笼子，并实施了20年的替代住房分步进度期。对不同品系鸡的骨量、结构，特别是组织水平材料特性的影响，目前还知之甚少。有趣的是，研究表明，自由奔跑的落地鸡舍或鸟舍系统中的母鸡骨骼更坚固，但与传统笼子中的母鸡相比，陈旧愈合的骨折(发生在种群减少之前)的数量更多。这些骨折的原因尚不清楚，尽管一些人推测它们是由于碰撞增加所致。目前尚不清楚骨骼对不同房屋提供的机械刺激的适应性如何导致骨折风险。在这个研究项目中，我将检查饲养在三种常用的商业可用系统中的母鸡，这三种系统提供不同程度的机械刺激。我将在产蛋期(18、32和54周龄)检测两个品系母鸡(Lohmann Brown和Lohmann Select Leghorn-Lite)在不同活动期间龙骨中产生的机械应变。我还将检查母鸡骨折和未骨折的龙骨骨量、微结构和质量，以确定骨折后的结果指标是否发生了变化。为了确定骨折期间的骨质量是否也在偏远部位恶化，我还将对患有和不患有龙骨骨折的成年母鸡的长骨(胫颧骨)进行这些分析。NSERC DG的短期目标是阐明母鸡龙骨骨折的病因。我的项目的长期目标是使用生物工程方法来了解鸟类的骨骼健康。这个项目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-机械刺激和矿物质动态平衡。这项研究计划准备为加拿大家禽养殖者提供有关龙骨骨折的病因以及住房环境如何可能导致骨折风险的信息，因为他们正在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.