Bone turnover in growing pigs fed three levels of dietary calcium

Abstract

The effect of dietary calcium level on bone quality and quantity was evaluated in growing pigs by means of histomorphometric methods as well as basic bone parameters and chemical indicators of bone turnover in the blood. Thirty growing pigs were allocated to three levels of dietary calcium, 3.5, 9.4 and 16.4 g kg−1DM, respectively. Blood was drawn five times throughout 62 d and analyzed for Ca, P, hydroxyproline, alkaline phosphatase and 1-carboxy terminal telopeptide (1CTP). On days 50 and 60 of the experiment, oxytetracycline was injected i.m. and the animals were sacrificed on day 62. Transiliac bone samples were obtained, processed undecalcified and used in morphologic and morphometric analyses. Medium or high dietary calcium resulted in a higher retention of calcium, and more bone mass as indicated by a higher trabecular bone volume and a lower bone resorption. The mineral appositional rate in the bones was also higher in these groups, indicating a fast growth rate. Conversely, a low dietary calcium supply, resulted in lower overall calcium retention, lower bone mass, and a higher extent of resorption lacunae and osteoid extent and width. Higher remodeling activity and osteoid accumulation were due to deficient mineralization as indicated by a lower mineralization rate and prolonged mineralization lag time. Bone markers in the blood were only slightly affected by the dietary calcium differences. It was concluded that the medium level of dietary calcium was sufficient to sustain sound bone development. Key words: Histomorphometric analysis, bone formation, bone resorption, hydroxyproline, cross-links, mineralization