Study On The Tolerance Of Laying Hens Exposed To The Sodium Bicarbonate

To explore the safe dose range of sodium bicarbonate in laying hens, this study wasconducted to investigate the effects of dietary supplement with NaHCO₃onperformance, hematological indices, histopathologic changes, the pH value andmositure content in feces, eggshell quality, mRNA expression levels of calciumtransport protein in the shell gland. Nine hundred21-week-old Hy-Line brown layinghens were randomly assigned to5groups with6replicates per group and30hens perreplicate. Laying hens were fed a basal diet with0（control,I）,1（II）,5（III）,25（IV）,50（V）g/kg NaHCO₃for10weeks, respectively. These conclusions were as follows:（1） Effects of dietary sodium bicarbonate on performance and hymnologicalindices in laying hens. The performance of laying hens was not influenced by dietaryNaHCO₃supplemental level at≤5g/kg （P>0.05）, but the laying rate, egg mass, feedintake, and average egg weight （P<0.05or P<0.01） were significantly reduced and theratio of broken and soft eggs （P<0.05） was significantly increased by dietary NaHCO₃supplemental level at≥25g/kg NaHCO₃. In addition, the concentrations of HCO3-andtotal CO2, partial pressure of CO2, base excess, and pH in blood of laying hens wereincreased with increasing NaHCO₃supplemental level, and significantly higher thanthose in the control group （P<0.05or P<0.01） except that1g/kg NaHCO₃did not affectpH and partial pressure of CO2（P>0.05）. Moreover, the supplementation of NaHCO₃didnot affect the number of red blood cells and white blood cells, the activities of alkalinephosphatase, glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase andthe concentrations of total protein, albumin, total bilirubin in serum of laying hens（P>0.05）. However, blood hematocrit and the concentrations of hemoglobin in blood（P<0.05or P<0.01） were markedly increased and the concentration of blood glucose inserum （P<0.05） were also significantly decreased by the supplementation of25to50g/kg NaHCO₃. Furthermore, the number of platelet in blood of laying hens in50g/kgNaHCO₃group was notably lower than that in the other groups （P<0.05）. It isconcluded that excessive supplementation of NaHCO₃（≥25g/kg） can cause the decrease of performance, change of blood gas indices, and disorder of physiologicalfunctions of laying hens. However, the supplementation of NaHCO₃at <5g/kg cansupport the performance and assistant to maintain hematological levels in thephysiological ranges of laying hens.（2） Change of histopathological observation in laying hens by supplement withsodium bicarbonate. The rate of mortality in25g/kg and50g/kg NaHCO₃groups weresignificantly higher than other groups （P<0.01）. And spleen, liver, kidney and heartcoefficients were also dramatically increased （P<0.05or P<0.01）, respectively. Inaddition, the concentrations of usea and creatinine nitrogen in serum （P<0.05or P<0.01）were markedly increased by the supplementation of25to50g/kg NaHCO₃. Themorphology of different organs showed that glomerular atrophy, the proximal and distalconvoluted tubule wall thinning, and the increase in the number of splenic white pulp inspleen, then liver necrosis and liver cell atrophy. In conclusion, excessivesupplementation of NaHCO₃（≥25g/kg） can cause the damage of liver, spleen andkidney.（3） Effects of dietary sodium bicarbonate on bacterial diversity of intestinalmicrobiota in laying hens. Compared with control, the number of Lactobacilli insupplementation1g/kg NaHCO₃group was increased, the number of E. coli wasdecreased, and the index of caecum bacterial diversity was also higher （P>0.05）. Insupplementation5g/kg NaHCO₃group, the pH value in feces was little higher than thatin the control group （P<0.05）, and the number of Lactobacilli and the index of caecumbacterial diversity were increased （P>0.05）, respectively. In addition, the pH value andmoisture content in feces from supplementation25g/kg and50g/kg NaHCO₃groupswere significantly increased compared with other groups （P<0.01）. However, insupplementation25g/kg and50g/kg NaHCO₃groups, the number of Lactobacilli wasdecreased （P>0.05or P<0.05）, but the number of E. coli was increased （P>0.05orP<0.05）, respectively. Moreover, the index of caecum bacterial diversity insupplementation50g/kg NaHCO₃group was lower than that in control,supplementation1g/kg and5g/kg NaHCO₃groups （P<0.05）, respectively. It isconcluded that excessive supplementation of NaHCO₃（2.5%） in dietary of laying henscauses serious diarrhea, and disorder of enterobacteria balance in caecum. However, thesupplementation level of NaHCO₃at5g/kg can facilitate the growth of beneficial bacterium and bacterial diversity in intestine, and maintain the laying performance.（4） Effect of dietary sodium bicarbonate on eggshell quality and its mechanism.Compared with control, the eggshell quality was not influenced by dietary NaHCO₃level at1g/kg or5g/kg （P>0.05）. However, the content of Ca²⁺in eggshell （P<0.01）,eggshell thickness and weight （P>0.05） were reduced in25g/kgand50g/kg group,respectively. In addition, eggshell strength and plasma Ca²⁺content were also notablyreduced by the supplementation of50g/kgNaHCO₃（P<0.05）. Then, the concentrationof VD level in plasma was dramatically improved by dietary NaHCO₃level at≥25g/kg（P<0.05or P<0.01）. Moreover, the mRNA expression of TRPV6, CaBP-D28k, PMCA1b and NCX1in ESG tissue were increased in≥25g/kg NaHCO₃groups （P<0.05）, butthe level of CA mRNA was remarkably reduced in50g/kg group （P<0.05）.Conclusion:the supplement of NaHCO₃at≤5g/kgcould not influence the eggshell quality.However, excessive supplement of NaHCO₃（≥25g/kg） can result in the decline ofeggshell quality. The mechanism may be related with lower plasma Ca²⁺content andESGCA mRNA level, then which lead to block to Ca²⁺transfer in ESG, finally result inthe reduction of eggshell quality. Secondly, the upper expression of TRPV6,CaBP-D28k, PMCA1b, and NCX1mRNA suggests that transcellular Ca²⁺transportpathway appears to compensate for low Ca²⁺intake in ESG.