| The synthesis and deposition of yolk precursors is the prerequisite for the formation of eggs,which plays a crucial role in laying eggs.In this study,the effects of light and temperature on the formation and deposition of egg yolk precursors in laying hens were observed.The specific mechanisms of these two factors were clarified,and a scientific basis for improving feeding environment and the egg production rate of poultry was provided.1.Effects of different light on the synthesis and deposition of egg yolk precursors in laying hens at the late stageWe selected 192 Hy-line Brown layers(77 wk),and divided them into 4 groups randomly and each group has 48 laying hens,control(16L:8D light),28 h treatment(13L:15D light),8+6h treatment(8L:5D:6L:5D light)and 14+1h treatment(14L:4D:1L:5D light).We measured egg production and egg weight daily,feed intake weekly,and egg quality fortnightly.After 8 weeks,blood samples,liver,dominant follicular membrane,small yellow follicular membrane and large white follicle membrane were collected on the fasting and feeding status.The results showed that the contents of TG and VTG in plasma and the expression of liver lipid synthesis related genes and proteins were not significantly affected by different light(P >0.05).The diameter and distribution of VLDL particles in plasma were significantly increased compared to the control group(P <0.05).The mRNA expression level of OVR and LPL(P <0.05)was significantly up-regulated,and the mRNA expression level of VLDLR and Occludin in the follicular membrane and the expression level of Occludin and Claudin-1 in the follicular membrane on the fasting and feeding state were not significantly increased(P >0.05).13L: 15 D light increased egg weight and yolk proportion(P <0.01),maybe due to the increase of OVR on the follicular membrane,thus promoting the deposition of the precursors of the yolk.Liver histomorphology showed no significant change between the two groups.2.Effects of mild high temperature on the synthesis and deposition of egg yolk precursors in laying hens at peak periodSelected 96 ISA Brown layers(36 wk)were divided into 3 groups randomly and each group has 32 hens,control(23±0.5?),temperature treatment(27±0.5?),feeding pairing group(23±0.5?,feed the test group for the day before every day).Egg production,egg weight and feed consumption of the test group were counted daily,and egg quality was measured fortnightly.After 8 weeks,blood samples,liver,dominant follicular membrane,small yellow follicular membrane and large white follicle membrane were collected on the fasting and feeding status.The results showed that 27±0.5? treatment had no significant effect on the content of TG and VTG,the diameter and distribution of VLDL particles in plasma(P >0.05),while the LXR gene mRNA expression level significantly up-regulated and the apo-B gene mRNA expression level significantly down-regulated(P <0.05).There was no significant difference in the expression of other genes and protein in the fasting and feeding state of liver(P >0.05).There were no significant differences in the expression of OVR,VLDLR,Occludin and LPL in the follicular membrane.Expression of Occludin and Claudin-1 protein in the follicular membrane has no significant differences(P >0.05).Mild high temperature(27±0.5?)reduced the production performance of laying hens,probably due to the decrease of feed intake(P <0.05).Liver histomorphology showed no significant change between different groups.13 L: 15 D light increased the deposition of precursor substance at the follicle to a certain extent.It may be because the light changed the rhythm of the laying hens and increased the expression of the receptor on the follicular membrane,thus enhancing the deposition of the yolk precursor.Mild high temperature(27±0.5?)decline in production performance may be due to a decrease in feed intake. |
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