Webster A B
Department of Poultry Science, University of Georgia, Athens, Georgia 30602-4356, USA.
Poult Sci. 2004 Feb;83(2):184-92. doi: 10.1093/ps/83.2.184.
Cage layer fatigue was first noticed after laying hens began to be housed in cages in the mid-20th century. Hens producing eggs at a high rate were most susceptible to the disease. Early research revealed that cage layer fatigue was associated with osteoporosis and bone brittleness. Severe osteoporosis leads to spontaneous bone fractures commonly in the costochondral junctions of the ribs, the keel, and the thoracic vertebrae. Vertebral fracture may damage the spinal cord and cause paralysis. Osteoporosis appears to be inevitable in highly productive caged laying hens. The condition can be made worse by metabolic deficiency of calcium, phosphorus, or vitamin D. Hens in housing systems that promote physical activity tend to have less osteoporosis and rarely manifest cage layer fatigue. Genetic selection may produce laying hens that are less prone to bone weakness. The welfare implications of osteoporosis stem from pain, debility, and mortality associated with bone fracture. The chicken has well-developed neural and psychological systems specialized to respond to pain associated with trauma and inflammation. Although studies on the chicken have not focused on pain due to bone fracture, physiological and behavioral similarities to other species allow inference that a hen experiences both acute and chronic pain from bone fracture. There is little information on osteoporosis in commercial caged layer flocks, however, evidence suggests that it may be widespread and severe. If true, most caged laying hens suffer osteoporosis-related bone fracture during the first laying cycle. Osteoporosis also makes bone breakage a serious problem during catching and transport of hens prior to slaughter. Estimates of mortality due to osteoporosis in commercial caged layer flocks are few, but range up to a third of total mortality. Many of these deaths would be lingering and attended by emaciation and possibly pain. Osteoporosis-related bone breakage during processing has reduced the marketability of spent caged laying hens, contributing to the need to develop humane on-farm killing methods to support alternative means of spent hen disposition. Overall, the evidence indicates that cage layer osteoporosis is a serious animal welfare problem. A determined effort must be made to make the laying hen no longer susceptible to the harmful effects of excessive bone loss.
笼养蛋鸡疲劳症最早在20世纪中叶蛋鸡开始笼养后被发现。产蛋率高的母鸡最易患此病。早期研究表明，笼养蛋鸡疲劳症与骨质疏松和骨骼脆性有关。严重的骨质疏松通常会导致肋骨肋软骨结合处、龙骨和胸椎自发骨折。椎骨骨折可能会损伤脊髓并导致瘫痪。在高产笼养蛋鸡中，骨质疏松似乎不可避免。钙、磷或维生素D的代谢缺乏会使病情恶化。在促进身体活动的饲养系统中的母鸡往往骨质疏松程度较轻，很少表现出笼养蛋鸡疲劳症。基因选择可能培育出不易出现骨骼脆弱的蛋鸡。骨质疏松对动物福利的影响源于与骨折相关的疼痛、虚弱和死亡。鸡具有发达的神经和心理系统，专门用于应对与创伤和炎症相关的疼痛。尽管对鸡的研究尚未聚焦于骨折引起的疼痛，但与其他物种在生理和行为上的相似性使人推断，母鸡会因骨折经历急性和慢性疼痛。关于商业笼养蛋鸡群中骨质疏松症的信息很少，然而，有证据表明它可能广泛且严重。如果情况属实，大多数笼养蛋鸡在第一个产蛋周期就会遭受与骨质疏松相关的骨折。骨质疏松还使得在屠宰前捕捉和运输母鸡时骨骼断裂成为一个严重问题。商业笼养蛋鸡群中因骨质疏松导致的死亡率估计很少，但高达总死亡率的三分之一。这些死亡中的许多将是迁延性的，伴有消瘦，可能还有疼痛。加工过程中与骨质疏松相关的骨骼断裂降低了淘汰笼养蛋鸡的市场价值，这促使人们需要开发人道的农场宰杀方法，以支持处理淘汰母鸡的替代方式。总体而言，证据表明笼养蛋鸡骨质疏松是一个严重的动物福利问题。必须下定决心，使蛋鸡不再易受骨质过度流失的有害影响。
