| Light regime plays a very important role in growth,development,reproductive maturity and reproductivity of laying hens.This research was based on the calcium transporters,carbonic anhydrase(CA)and matrix protein in kidney and eggshell gland.In changing the light regime which frequently used in laying hens production,this research discussed how light regime affected laying hens at different growth stages.The relationship between light regime,calcium transporters(Calcium-binding protein-D28 k and plasma membrane Ca ATPase 1b),carbonic anhydrase and matrix protein was also studied.Furthermore,this research examined the mechanism by which light regime affected eggshell quality;and it also provides recommended reference for selection of light regimes during late laying period in hens.Experiment one: Effect of different treatments of illumination on the bone development and subsequent productivity of laying hens during the replacement period.A total of 216 ISA Brown layers,at 9 weeks of age were randomly selected and divided into three groups for this experiment.Group one adopted constant 8 h illumination for layers aged 10 to 18 weeks old(C 8).Group two was subjected to decreasing illumination at 1 h per week based on the previous 14 h illumination until 8 h length of the illumination was reached(D 1).Group three was treated by decreasing illumination 2 h per week from the previous 14 h illumination until 8 h length of the illumination was achieved(D 2).Data collection was obtained every week.After 8 weeks of experiment,the layers were transferred to the commercial hen house for follow-up observations.Result showed that the body oblique length and chest circumference of D 2 at 14-16 weeks old layers were significantly(P<0.05)smaller than the other two groups,and the laying rate of 8 h illumination treatment maintained a high level for a longer period compared to others.Experiment two: Effect of different light regime on the reproductive productivity and calcium transporters expression of Hy-Line Brown layers.This experiment selected 96 Hy-Line Brown layers aged 78-weeks-old and they were randomly divided into two groups.First group adopted 16 L:8 D light regime(a period of 24 h),and the second adopted 13 L:15 D light regime(a period of 28 h).The laying rate and average egg weight of layers were recorded daily;the feed intake was determined weekly and the egg quality was detected fortnightly.The experimental period was 8 weeks.At the end of experiment,each group was divided into four time points for collection of eggshell glands,kidney samples,and bone samples.Result showed that the egg weight of group 13 L:15 D was significantly increased(P<0.05);the thickness and strength of eggshells were significantly improved(P<0.05);and during the night,the mRNA expression level of PMCA1 b and the concentration of CA were also significantly increased compared with the 16 L:8 D treated group(P<0.05).These results indicated that the prolongation of photoperiod an increase of dark time led to the improvement of eggshell quality,which may be closely related to the increase of CA concentration.Experiment three: Effect of different illumination time on the reproductivity and calcium transporters expression of 36-weeks-old(high egg production)ISA Brown layers.240 ISA Brown layers at 36 weeks of age were selected and divided into 4 treatment groups of 16 L:8 D,13 L:15 D,13 L:11 D and 9 L:15 D light regimes respectively.The laying rate was recorded every day,the feed intake was determined weekly and egg quality was determined.After 8 weeks of experiment,the kidney,eggshell gland and blood samples of layers in group 16 L:8 D were collected.Samples were respectively collected at the midpoint of day and night.The serum ALP level and laying rate of 16 L:8 D group were significantly higher than the other groups(P<0.05).The matrix protein OPN and OC-116’s expression showed obvious circadian rhythm,with the expression at night being significantly higher than at day(P<0.05);whereas the CA concentration of group 13 L:15 D was significantly higher than other groups.These results indicated that reduction of illumination time or an increase in photoperiod led to the decline in laying rate,and the improvement of the eggshell quality may be related to the increase of CA concentration.Experiment four: Effect of different illumination time on the reproductivity and calcium uniporter expression of 83-weeks-old(late laying period)ISA Brown layers.192 ISA Brown layers at 83 weeks of age were selected and randomly divided into 4 treatment groups.Each treatment had 6 replicates with 8 hens per replicate subjected to 16 L:8 D,14 L:10 D,12 L:12 D and 10 L:14 D light regimes per treatment respectively.The experiment lasted 8 weeks and egg quality was determined fortnightly.At the end of experiment,the kidney,eggshell gland and blood samples of layers from group 16 L:8 D and 10 L:14 D the midpoint of day and night.Results indicated that illumination treatments did not affect the laying rate of all group(P>0.05);the thickness of eggshell in group 10 L:14 D was significantly increase(P<0.05).The mRNA expression of CaBP-D28 k and OPN was significantly different at day and night.Also,it was observed that for the old layers,the prolongation of dark time could increase the thickness of eggshell without affecting optimal reproductivity. |
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