Effect of photoperiod on growth performance and quality characteristics of tibia and femur in layer ducks during the pullet phase.

This study aimed to evaluate the effect of photoperiod on growth performance and bone development in layer ducks during the pullet phase. A total of 480 11-wk-old Jinding layer ducks were randomly divided into 5 groups, receiving 6L (light): 18D (dark), 8L: 16D, 10L: 14D, 12L: 12D, 14L: 10D, respectively. Each group had 6 replicates of 16 birds each. The feeding trial lasted 80 d until 150 d of age. The results showed that 8L: 16D increased body weight (BW) and average daily gain (ADG; P < 0.05) compared with 6L:18D, whereas average daily feed intake, feed conversion ratio, and mortality rate had no difference among all treatments (P > 0.05). The midpoint perimeter (tibia and femur) and work to fracture (Wu; tibia) increased quadratically (P < 0.05), in response to photoperiod increment. Compared with 6L:18D, 8L:16D had higher tibia midpoint perimeter, ultimate load (Fu), and cortical cross-sectional area (P < 0.05), accompanied with higher content of total Ca, distal bone mineral content (BMC), and cortical volumetric BMC (vBMC; P < 0.05). A linear increase was observed in trabecular volumetric bone mineral density (vBMD) and vBMC (tibia and femur), elastic energy (femur), work to fracture Wu and young modulus of elasticity E (tibia) in response to photoperiod increase (P < 0.05), and treatment with 14L:10D had higher ultimate load Fu and total Ca of tibia (P < 0.05). Besides, estradiol and testosterone levels (serum), estrogen receptor gene mRNA expression (bone tissue), alkaline phosphatase and tartrate-resistant acid phosphatase activities, transforming growth factor-β, osteocalcin and tumor necrosis factor-α contents increased in ≥12 h photoperiods (P < 0.05). In summary, appropriate photoperiod increased BW, ADG, cortical bone generation, and bone mineralization, whereas only medullary bone formation increased with photoperiods. These results suggest that 8L:16D could be an adequate photoperiod for layer ducks' growth and bone development during the pullet phase.