This study investigated the effects of dietary energy and calcium levels on laying performance, eggshell quality and bone metabolism of layers. One hundred and sixty-two 19-week-old Hy-Line brown laying hens in 54 battery cages were allocated to one of nine dietary treatments with control, middle and high levels of energy (11.50, 12.68 and 13.37 MJ/kg, respectively) and low, control and high levels of calcium (2.62%, 3.7% and 4.4%, respectively) for 60 days, using a 3 × 3 factorial arrangement. Compared with the control energy diet, high- and middle-energy diets increased fat deposition and egg weight, decreased feed intake and bone quality and had no effects on eggshell quality. The high-energy diet reduced the serum phosphate concentration and elevated osteocalcin mRNA expression in the keel bone without increasing osteocalcin protein. Dietary calcium intake did not affect fat deposition, feed intake or egg weight. Low dietary calcium resulted in weaker eggshells and poorer bone quality than that from hens fed the control diet. High dietary calcium increased serum calcium concentration, osteoprotegerin mRNA and osteocalcin protein and inhibited serum alkaline phosphatase activity and decreased its mRNA compared with low or control dietary calcium. The high-energy and high-calcium diet significantly reduced egg production. Compared with the control energy diet, high- and middle-energy diets increased fat deposition but had negative effects on bone metabolic homeostasis. Dietary calcium did not influence fat deposition but a high-calcium diet benefited bone homeostasis, while a low-calcium diet was associated with poorer eggshell quality and bone homeostasis.
Keywords: Bone metabolic homeostasis; Calcium; Energy; Laying hens; Osteocalcin.
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