| Layer duck production accounted for 15%of all egg consumption in 2011,and increased rapidly in recent years.Layers are sensitive to light,so photoperiod could regulate their laying performance.This study investigated the effect of photoperiod on productive performance,bone metabolism,reproductive organs and hormone levels of layer ducks,during the pullet and laying phases.Experiment 1:Effect of photoperiod on growth performance and bone development in layer ducks during the pullet phase.A total of 480 71-d-old Jinding laying ducks were randomly divided into 5groups,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 days 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,while 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 with14L: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-?,osteocalcin and tumor necrosis factor-?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 increasing photoperiods.These results suggested 8L:16D could be an adequate photoperiod for laying ducks'growth and bone development during the pullet phase.Experiment 2:Effect of photoperiod on ovarian morphology,reproductive hormone secretion and hormone receptor mRNA expression in layer ducks during the pullet phase.Four hundred eighty71-d-old Jinding layer ducks were randomly divided into five groups that received 6L:18D,8L:16D,10L:14D,12L:12D or 14L:10D,respectively.Each group had six replicates with 16 birds each.The photoperiod feeding trial lasted 80 d until 150 d of age.The age at first egg(AFE),the total number and weight of eggs increased linearly with increasing photoperiods(P?0.05);lower values of AFE occurred with photoperiods?8 h,whereas a higher total number and weight of eggs occurred with photoperiods?10 h,compared with 6L:18D(P?0.05).Oviduct weight,ovary percentage,initial and bare stroma(weight and percentage)increased quadratically with increasing photoperiods(P?0.05),and 10.24,10.01 and 10.10 h were the optimal photoperiods for oviduct weight,bare stroma(follicles?2 mm in diameter removed)weight and bare stroma percentage,respectively,as calculated from reliable regression equations(R~2?0.5791).Compared with 6L:18D,10L:14D had a higher total large white follicle weight,small yellow follicle number and weight(P?0.05).In addition,higher serum levels of follicle-stimulating hormone,luteinizing hormone and progesterone were observed with?10-h photoperiods(P?0.05),as were levels of hormone receptor mRNA expression in ovarian follicles(P?0.05),with the highest values for both measures at 10L:14D.In the hypothalamus,mRNA expression of gonadotropin-releasing hormone increased in?8-h photoperiods,with the highest value at 10L:14D.In contrast,gonadotropin-inhibitory hormone increased in photoperiods?12 h(P?0.05).In conclusion,an appropriate photoperiod led to early sexual maturity and improved the development of reproductive organs and ovarian follicles through effects on reproductive hormones and their receptors;10-10.24 h is an adequate photoperiod for layer ducks during the pullet phase.Experiment 3:Effect of photoperiod on laying performance,reproductive organs and ovarian follicles development in laying ducks.A total of 300 252-d-old Jinding laying ducks were fed a basal diet,with pellet form.They were randomly divided into five groups that received 12L:12D,14L:10D,16L:8D,18L:6D or 20L:4D,respectively.Each group had six replicates with 10 birds each.The feeding trial lasted from 37 to 44 wk of age.Egg production,egg mass and average daily feed intake(ADFI)increased lineally and quadratically with increasing photoperiods(P?0.05),during 1-4,5-8 and 1-8 wk.Compared with the 12L:12D,?16 h photoperiod increased egg production(5-8 and 1-8 wk),egg mass(1-4,5-8 and 1-8 wk)and ADFI(1-4,5-8 and 1-8 wk;P?0.05).Besides,more than 16 h photoperiod treatments had higher egg production(1-4 wk)than those of 12L:12D and 14L:10D treatments.The initial stroma(weight)and bare stroma(weight and percentage)increased quadratically in response to the increase in photoperiod(P?0.05).The total number and weight of LWF increased linearly and quadratically with increasing photoperiods(P?0.05).Reliable regression equations(R~2?0.5071)were obtained;16.56 and 16.93 h were the optimal photoperiod for bare stroma and LWF weight,respectively.Compared with the 12L:12D,16L:8D treatment had higher initial stroma weight,bare stroma weight and percentage(P?0.05);meanwhile,higher values of initial and bare stroma weight were observed in18L:6D treatment(P?0.05).More than 16 h photoperiod increased LWF weight,and the higher values occurred in 16L:8D and 18L:6D treatments(P?0.05),compared with the 12L:12D.Besides,total number of LWF in 16L:8D and 18L:6D were higher than those of 12L:12D and 14L:10D treatments(P?0.05).Appropriate photoperiod could improve laying performance,reproductive organ and ovarian follicles development,and 16.56-16.93 is an adequate photoperiod for laying ducks.Experiment 4:Effect of photoperiod on bone and eggshell quality of laying ducks.A total of 300252-d-old Jinding laying ducks were fed a basal diet,with pellet form.They were randomly divided into five groups that received 12L:12D,14L:10D,16L:8D,18L:6D or 20L:4D,respectively.Each group had six replicates with 10 birds each.The feeding trial lasted from 37 to 44 wk of age.The ultimate load(Fu)of tibia and ulna,distance at fracture(d-Fu)of ulna increased lineally and quadratically with increasing photoperiods(P?0.05),and 17.79 h was the optimal photoperiod for Fu of femur,based on reliable regression equation(R~2=0.5078).The higher value of Fu of tibia was observed in 18L:6D than other treatments(P?0.05);the higher Fu of femur and ulna occurred in 18L:6D compared with those of12L:12D and 14L:10D treatments(P?0.05).The cortical cross-sectional area(A)at the midpoint increased linearly(femur)and quadratically(femur and ulna)in response to the increase in photoperiods(P?0.05).The cortical cross-sectional area(A)in 18L:6D was higher than those of 12L:12D and14L:10D treatments in tibia and femur(P?0.05),than 12L:12D,14L:10D and 20L:4D treatments in ulna(P?0.05).At the end of 4 wk,the higher value of eggshell breaking strength was observed in18L:6D compared with those of 12L:12D and 14L:10D treatments(P?0.05);at the end of 6 wk,the higher eggshell breaking strength occurred in 18L:6D and 20L:4D,compared with those of 12L:12D and 14L:10D treatments(P?0.05).In summary,appropriate photoperiod could improve the bone and eggshell quality,and 17.79-18 h could be an adequate photoperiod for laying ducks.Appropriate photoperiod could improve the development of bone and reproductive system during the pullet phase,and bone quality and reproductive performance during the laying phase;the optimal light time during these two phases were 8-10.24 and 16.56-18 h/d,respectively. |
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