Possibilities of monitoring bone metabolism in ruminants--an overview of the methods in use.

Abstract

Bone metabolism in humans and several animal species can be monitored in vivo by measuring enzymes and other protein products released by osteoblasts and osteoclasts, respectively. Bone mineral density (BMD) and content (BMC) can be determined by peripheral quantitative computer tomography (pQCT). Another approach is to measure histomorphometric indices of bone biopsies. The biochemical markers of bone formation currently in use include bone isoenzyme of alkaline phosphatase, osteocalcin and propeptides derived from the N or C terminal ends of the type I procollagen molecule. The longest established method for the measurement of bone resorption is hydroxyproline in urine. However, it is not specific for bone, since it is found in all collagen types and it can also derive from the diet. The most useful markers of bone resorption are breakdown products of type I collagen. The measurement of collagen crosslinks, deoxypyridinoline and pyridinoline, is comparatively more specific to monitor bone resorption. Deoxypyridinoline and pyridinoline are of use in human medicine in the diagnosis and evaluation of bone diseases and in the prediction of the occurrence of fractures and the rates of bone loss. The carboxyterminal telopeptide of type I collagen, which has been used in several animal species, is also a promising bone resorption marker. This overview gives a general idea about the use of different bone markers and measurements of other bone parameters in ruminants during growth, gestation and lactation in relation to calcium metabolism.