| Many researches have shown that there is a close and complicated relation between energy and bone metabolism. Meanwhile the bone metabolism of laying hens is influence by dietary Ca supply. To investigate the effect of dietary energy on bone metabolism in early laying period of cage layers,10819-wk-old hens were randomly divided into a3×2factorial treatments with one control group, that is, normal energy and normal calcium group (NENC,11.5MJ·kg-1energy and3.7%Ca) and five experimental groups, that is, middle energy and normal calcium group (MENC,12.68MJ·kg-1energy and3.7%Ca), high energy and normal calcium group (HENC,13.37MJ·kg-1energy and3.7%Ca), normal energy and low calcium group (NELC,11.5MJ·kg-1energy and2.62%Ca), middle energy and low calcium group (MELC,12.68MJ·kg-1energy and2.62%Ca) and high energy and low calcium group (HELC,13.37MJ·kg-1energy and2.62%Ca). The trial lasted for75days. The role of dietary energy in the process of bone metabolism could be revealed by detecting laying performance, egg shell quality, bone biology indicators, and the mRNA expressions of genes and proteins related to bone metabolism, etc.Egg production, cracked egg rate and mortality rate were recorded daily during the experiment. Feed intake, egg weight, shell breaking strength, egg shell thicknesss as well as blood sample for OCN content was determined, and the mRNA expression of OPG, RANKL, ALP and OCN, as well as the OCN protein in the keel were detected in the end of trial.As a result, in terms of productivity and egg shell quality, feed intake decreased with the increase of energy level(P<0.05), especially in middle and high energy groups(P<0.05). Total cracked egg rate increased with dietary energy level (P<0.05), but after wk8, the energy effect disappeared. The overall eggs became heavier as the energy level increased(P<0.05), with middle and high energy groups’egg weights significantly higher than control groups(P<0.05). And in stage3, low Ca group had lower egg weights (P<0.05). Low Ca group had a decreased egg fracture load (P<0.05), with control and MENC group significantly higher than high energy and MELC group in stage3(P<0.05).As to bone metabolism traits, relative bone weight of femurs and tibias had an inverse relation with energy (P<0.05). Density of femurs and tibias decreased as energy level rise (P<0.05). Maximum load of tibias in high energy group was significantly lower (P<0.05). Both stiffness and Young’s modulus of two bones became lower with the rise of energy level(P<0.01). In keel, the ALP mRNA in high energy groups were higher than middle energy groups(P<0.05). The rise of dietary energy increased OCN mRNA expression (P<0.01), whereas the OCN protein were not influenced. Energy had no significant effect on OPG and RANKL expression (P>0.05).In conclusion, egg production was not affected by energy. The cracked egg rate increased with energy level, but this influence disappeared after the peak of layering in hens. Feed consumption was significantly inhibited by dietary level, while the Ca only had a slighter influence. The rise of dietary energy benefited egg weight, whereas the Ca decreased egg weight. The egg shell thickness and breaking strength not varied greatly except the condition of low Ca diet, when increase of energy deteriorate egg shell quality.Elevation of ALP and OCN expression suggested an increase of OB cell activity. The experiment resiuls revealed the negative effect of dietary high energy level on bone traits, causing a decrease in bone weight, density and biomechanical properties. Therefore, considering both bone biological traits and OCN of the blood and keel bone, we assume that the bone resorption was elevated with increased bone formation by high energy diet. Consequently, the high bone turnover including formation and resorption speeded up the loss of bone mass and deteriorate osteoporosis. |
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