Both genetic selection and increasing nutrient density for improving growth performance had inadvertently increased leg problems of meat ducks, which adversely affects animal welfare. We hypothesised that slowing weight gain with improving tibia quality probably enhanced tibial mechanical properties and alleviated leg deformities. Therefore, the present study aimed to evaluate the effect of graded Ca supplementation in a low-nutrient density (LND) diet on tibia composition and bone turnover in meat ducks. A total of 720 15-d-old male meat ducks were randomly assigned and fed a standard nutrient density positive control (PC) diet containing 0·9 % Ca, and four LND diets with 0·5, 0·7, 0·9 and 1·1 % Ca, respectively. Ducks fed the 0·5 % Ca LND diet and the PC diet had higher incidence of tibial dyschondroplasia (TD). When compared with the 0·5 % Ca LND diet, LND diets with ≥0·7 % Ca significantly improved tibia composition, microarchitecture and mechanical properties, and consequently decreased the incidence of TD. Furthermore, LND diets with ≥0·7 % Ca increased osteocyte-specific gene mRNA expression, blocked the expression of osteoblast differentiation marker genes including osteocalcin, collagenase-1 and alkaline phosphatase (ALP), and also decreased the expression of osteoclast differentiation genes, such as vacuolar-type H+-ATPase, cathepsin K and receptor activator of NF-κB. Meanwhile bone markers such as serum ALP, osteocalcin (both osteoblast markers) and tartrate-resistant acid phosphatase (an osteoclast marker) were significantly decreased in at least 0·7 % Ca treated groups. These findings indicated that LND diets with ≥0·7 % Ca decreased bone turnover, which subsequently increased tibia quality for 35-d-old meat ducks.