Effect of photoperiod on eggshell quality and quality characteristics of tibia, femur, and ulna in laying ducks.

We investigated the effect of photoperiod on eggshell quality, bone quality characteristics and bone metabolism related enzymes and factors in laying ducks. After adaption, 300 Jinding laying ducks (252-day-old) were randomly divided into 5 treatments, receiving 12L (hours of light):12D (hours of darkness), 14L:10D, 16L:8D, 18L:6D or 20L:4D, respectively. Each group had 6 replicates of 10 birds each. The feeding experiment lasted 8 wk. Compared with 12L:12D, the higher values of eggshell breaking strength occurred in ≥18 h photoperiods at the end of 6 wk, and in ≥16 h photoperiods at the end of 4 wk, with the common highest values in 18 h photoperiod (P ˂ 0.05). Besides, 18L:6D had higher values of ultimate load Fu and cortical cross-sectional area A in tibia, femur, and ulna (P ˂ 0.05), compared with 12L:12D. The higher values of proximal bone mineral content (BMC; tibia), distal BMC (ulna), total Ca (tibia), and cortical volumetric bone mineral density (vBMC; tibia and ulna) were observed in 16L:8D and 18L:6D treatments (P ˂ 0.05). Meanwhile, 18 h photoperiod group had the higher proximal BMC (femur) and total Ca in ulna (P ˂ 0.05). In serum, compared with 12L:12D group, the higher ALP activity occurred in ≥16 h photoperiods (0:00 and 18:00), with the highest values in 18L:6D treatment (P ˂ 0.05); the higher values of TGF-β (6:00) and OC (6:00 and 18:00) were simultaneously observed in 18 h photoperiod (P ˂ 0.05). Moreover, values of trACP activity, TNF-α and IL-6 contents decreased in ≥18 h photoperiods at 0:00 (P ˂ 0.05), compared with 12L:12D group. To sum up, an appropriate photoperiod could improve eggshell quality, bone strength and mineral content through increasing osteogenesis during the light time and decreasing resorption activity during the dark, and 18 h is an adequate photoperiod for the eggshell and bone quality of laying ducks.