Porr C A, Kronfeld D S, Lawrence L A, Pleasant R S, Harris P A
Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA.
J Anim Sci. 1998 Jul;76(7):1875-9. doi: 10.2527/1998.7671875x.
Diet and exercise are two management factors that affect bone density and strength. We proposed that bone density and calcium status would be affected by deconditioning for 12 wk and by dietary Ca concentration. Eleven highly conditioned Arabian horses were taken out of training and placed in stalls for 12 wk. Horses were walked on a mechanical walker in two 30-min sessions, 7 d/wk. Diets were designated CC (.36% Ca) and HC (.62% Ca). Data were collected every 21 d. Serum or plasma were analyzed for total and ionized Ca, parathyroid hormone, osteocalcin, hydroxyproline, electrolytes, and blood gases. Bone mineral content (BMC) of the left third metacarpal bone was estimated by radiographic photometry using an aluminum step wedge, which was exposed in each radiograph, as a reference standard for an image analysis system. During deconditioning, BMC decreased by approximately 1.1 g/2 cm, or .45% per week. This decrease was unaffected by dietary Ca. Serum Ca concentration increased with deconditioning. The results suggest that dietary Ca at twice the currently recommended level did not prevent the loss of BMC in response to deconditioning. Loss of BMC during 12 wk of stall confinement may weaken bones, increasing the risk of skeletal injuries when training is resumed.
饮食和运动是影响骨密度和强度的两个管理因素。我们提出，为期12周的失用状态和饮食中钙的浓度会影响骨密度和钙状态。11匹训练有素的阿拉伯马停止训练，关进马厩12周。马匹每周7天，分两个30分钟时段在机械步行器上行走。日粮分为CC（含钙0.36%）和HC（含钙0.62%）。每21天收集一次数据。分析血清或血浆中的总钙、离子钙、甲状旁腺激素、骨钙素、羟脯氨酸、电解质和血气。使用铝阶梯楔通过放射光度法估算左第三掌骨的骨矿物质含量（BMC），铝阶梯楔在每张X光片中都有显示，作为图像分析系统的参考标准。在失用状态期间，BMC每周下降约1.1 g/2 cm，即0.45%。这种下降不受日粮钙的影响。血清钙浓度随着失用状态而升高。结果表明，日粮钙含量为当前推荐水平的两倍时，不能防止因失用状态导致的BMC流失。在马厩禁闭12周期间BMC的流失可能会使骨骼变弱，增加恢复训练时发生骨骼损伤的风险。
