Effect of Milk on Bone Metabolism in Growing Male and Female Rats

Abstract

To investigate the effect of milk on bone metabolism in growing rats, the bone mineral density (BMD), bone strength and intestinal calcium (Ca) absorption were examined. It has recently become possible to accurately and precisely measure BMD in growing animals with low bone mass by a bone densitometer. In this study, the change in BMD in growing young rats was therefore evaluated by this method.
Male and female Sprague-Dawley (SD) rats at 3 weeks of age were divided into male and female control diet groups (0.3% Ca from CaCO₃) and milk diet groups (0.3% Ca from milk). The experimental period lasted for 4 weeks. The change in BMD and the intestinal Ca absorption were determined in experiment A (Exp. A), and BMD of the extracted bone, mechanical bone strength, and weight and mineral contents of the bone were measured in experiment B (Exp. B).
In Exp. A, BMD in the lumbar spine and tibia of the milk diet groups increased significantly compared to those of the control values. The intestinal Ca absorption of the rats in the milk diet groups was also significantly greater than that of the control rats. In addition, in Exp. B, BMD values, mechanical bone strength, bone weight, and Ca and P contents in the bone of the rats in the milk diet groups were also significantly greater than the control values.
These findings suggest that milk promoted bone metabolism during the growing period and confirm the effectiveness of measuring BMD of low bone mass by a bone densitometer to evaluated metabolism in vivo.