The effect of increased gravitational stress on bone

To assess the effects of an altered gravitational state on the physical properties of bone, fifteen sexually mature chickens were centrifuged for 18 weeks. The gravitational forces were gradually increased to allow the chickens to adapt to the increased load. For the last 4 weeks of the experiment, the animals were subjected to a force of 3 x gravity. After sacrifice the tibias were removed and fractured in torsion. Bone diameters, cortical thickness and ash content of the tibias were determined. Histological preparations of the bone specimens were also examined. When the centrifuged animals were compared with control chickens of comparable size and weight, there was no significant change in bone strength or fracture pattern, although the centrifuged birds had smaller mid-tibial shaft diameters and thicker cortices. The mean percentage bone ash for the centrifuged birds was 68.2% which is an accepted value for dry bone ash of adult chickens. Bone density was the same for both centrifuged and control birds. The birds lost an average of 465 grams of body mass during their 18 weeks on a centrifuge.