Effect Of Dietary Na₂SO₄ Supplementation On Eggshell Quality And Ion Transport In Laying Hens

Eggshell quality is an important character of eggs.To meet the laying hens’needs of Na,about 0.3%salt（sodium chloride,Na Cl）is usually added to the diets in practice production.Because the contents of Cl and Na of salt are 59%and 39.5%,the suitable Na addition made the content of Cl increased up to～0.22%,when 0.3%salt was supplemented in diets.Dietary level of Cl below 0.2%was unfavorable to eggshell quality.Sodium sulfate（Na₂SO₄）is an alternative and cost effective Cl-free source of Na for poultry To improve eggshell quality,balance the dietary Na and Cl levels of laying hens and explore the rational use of Na Cl and Na₂SO₄,this study were performed to evalute the effect of dietary Cl levels on performance,eggshell mechanical quality and ultrastructure in layers based on the substitution of Na Cl by Na₂SO₄.And on the basis of the best replacement effect,the effect of dietary Na levels on performance and eggshell quality in layers were then studied based on the supplemental Na₂SO₄.Experiment 1 was conducted to evaluate the effect of dietary Cl levels on performance,eggshell mechanical quality,eggshell calcium（Ca）content,electrolyte values in blood and uterine fluid and relative m RNA expressions of ion transporters at 18.5h post oviposition（PO）and ultrastructure in layers based on the substitution of Na Cl by Na₂SO₄.A total of 360 Hy-brown laying hens were used in this work.Birds were randomly allotted into 5 groups that consisted of 8replicates with 9 birds each and fed corn-soybean diets with 0.06%,0.10%,0.15%,0.20%,0.25%Cl contained feed,respectively.The results showed the 0.06%Cl level obtained by completely replacing Na Cl with Na₂SO₄had adverse effects on the performance of laying hens（45-54wk）（P<0.05）,increased the concentration of serum CRE（P<0.05）,and caused visible renal tubular injury.（2）The strength,thickness,weight and Ca content of whole and 18.5h PO（linear deposition period）eggshells were all affected by different Cl levels（P<0.05）.When dietary Cl levels were0.10%and 0.15%,the eggshell strength,eggshell thickness,eggshell weight and Ca content of whole and 18.5h PO eggshell were better（P<0.05）（3）Compared with 0.06%Cl level and 0.25%Cl level,the total thickness and effective thickness of eggshell were significantly increased（P<0.05）,while the thickness of mastoid layer was significantly decreased（P<0.05）.In addition,dietary Cl level linearly and quadratically（P<0.05,respectively）affected Cl retention,potassium ion（K⁺）,sodium ion（Na⁺）,Cl^-and bicarbonate ions（HCO₃^-）concentrations in blood and Cl^-concentration in uterine fluid at 18.5h PO.Blood p H,uterine K⁺,HCO₃^-and Ca²⁺concentrations were quadratically（P<0.05,respectively）affected by Cl levels in diets.Besides,the m RNA expression levels data showed that compared with 0.10%and 0.15%Cl groups,the 0.06%Cl decreased（P<0.05）the Ca²⁺/Na⁺exchangers（SLC8A3）,HCO₃^-/Cl^-exchangers（SLC26A9）,carbonic anhydrase 2（CA2）and Cl^-/H⁺exchanger（CLCN5）m RNA expression levels and 0.20%and 0.25%Cl reduced（P<0.05）SLC26A9 and CLCN5 m RNA expression levels at 18.5h PO.In conclusion,the complete substitution of dietary Na Cl by Na₂SO₄depressed laying performance and eggshell quality.Na₂SO₄could partly replace Na Cl in diets for laying hens（43 to 54 wk of age）without adverse effects on performance at the dietary Cl level from 0.10%to 0.25%.Dietary Cl levels from 0.06%to 0.25%had a quadratic effect on Ca deposition and thus affecting eggshell quality of laying hens（43 to 54 wk of age）.During the linear deposition stage,dietary Cl levels from 0.06%to 0.25%affected the Ca deposition mainly through the ion transport process.Experiment 2 was conducted to evaluate the effect of dietary Na levels on performance,eggshell mechanical quality,eggshell Ca content,electrolyte values in blood and uterine fluid and relative m RNA expressions of ion transporters at 18.5h post oviposition（PO）,eggshell GAGs contents,ATPase and SULT contents in isthmus and ultrastructure in layers based on supplemental Na₂SO₄.A total of 432 Hy-brown laying hens were used in this work.Birds were randomly allotted into 6 groups that consisted of 8 replicates with 9 birds each and fed corn-soybean diets with 0.15%,0.20%,0.25%,0.30%,0.35%,0.40%Na contained feed,respectively.The results showed on the premise of the best Cl level,supplemental Na₂SO₄in diets had no adverse effect on the performance of laying hens（49-60wk）.Dietary Na levels based on supplemental Na₂SO₄quadratically affected egg yolk color,breaking strength,thickness,eggshell Ca contents,weight of eggshell and shell ratio（P?0.05）.Besides,compared to the 0.15%and 0.40%Na groups,total thickness,effective thickness significantly increased（P?0.05）and mammillary thickness decreased（P?0.05）in the 0.30%Na group.Eggshell GAGs contents and ATPS and SULT contents in isthmus of laying hens increased（P?0.05）in the group of dietary 0.30%Na compared to the groups of 0.15%Na.In addition,dietary Na level linearly and quadratically（P<0.05,respectively）affected sodium ion（Na⁺）concentrations in blood and potassium ion（K⁺）and Na⁺concentration in uterine fluid at 18.5h PO.Uterus Ca²⁺concentrations were quadratically（P<0.05,respectively）affected by Na levels in diets.Besides,the m RNA expression levels data showed that compared with 0.15%and 0.20%Na groups,the 0.30%Na increased（P<0.05）the Ca²⁺/Na⁺exchangers（SLC8A1）,sodium channel SCNN1A m RNA expression levels.Compared with 0.35%and 0.40%Na groups,the 0.30%Na increased（P<0.05）Na⁺/K⁺exchangers ATP1B1and potassium channel KCNMA1 m RNA expression levels at 18.5h PO.In conclusion,dietary Na level from 0.15%to 0.40%based on supplemental Na₂SO₄had no adverse effects on performance.Better eggshell quality could be obtained when Na₂SO₄supplemented in laying hen diets maintaining Cl level at 0.30%.Dietary Na levels from 0.15%to 0.40%had an effect on eggshell quality result from increased sulfated GAG contents in eggshell and improved Ca deposition of laying hens（49 to 60 wk of age）.During the linear deposition stage,dietary Na levels from 0.15%to 0.40%affected the Ca deposition mainly through the ion transport process.In summary,the conclusion showed as follows:dietary Cl level from 0.10%to 0.25%obtained when Na Cl was partly replaced by Na₂SO₄and dietary Na level from 0.15%to 0.40%based on supplemental Na₂SO₄both had no adverse effects on performance.Better eggshell quality could be obtained when Cl levels was 0.15%obtained when Na Cl was partly replaced by Na₂SO₄and Na levels was 0.30%by Na₂SO₄supplemented in laying hen diets.Dietary Cl levels from 0.10%to 0.25%and dietary Na levels from 0.15%to 0.40%had an effect on eggshell quality result from improved Ca deposition of laying hens through the ion transport process.Besides,dietary Na levels from 0.15%to 0.40%increased sulfated GAG contents in eggshell to improve eggshell quality.