Dietary chloride levels affect performance and eggshell quality of laying hens by substitution of sodium sulfate for sodium chloride

The objective of this study was to evaluate the effect of dietary chloride (Cl) levels on performance, eggshell mechanical quality, and ultrastructure in layers based on the substitution of sodium chloride (NaCl) by sodium sulfate (Na₂SO₄). Three hundred sixty Jing Brown laying hens aged 43 wk were randomly divided into 5 groups and fed with corn–soybean meal diets containing 0.06, 0.10, 0.15, 0.20, and 0.25% total Cl inclusion. Every group had 8 replicates of 9 birds each. The feeding trial lasted for 12 wk. The results showed dietary 0.06% Cl due to complete substitution of NaCl by Na₂SO₄, depressed performance (P < 0.05) from 45 to 54 wk of age, increased serum creatinine level (P < 0.05), and caused visible renal tubular atrophy. Dietary Cl levels quadratically affected breaking strength, thickness, and weight of eggshell (P < 0.05). Better eggshell quality could be obtained when NaCl was partly replaced by Na₂SO₄ in laying hen diets maintaining Cl level at 0.10 or 0.15%. Moreover, the eggshell ash content was affected by Cl levels in a quadratic (P < 0.001) manner, with higher values observed in the 0.10 and 0.15% Cl groups (P < 0.05). Besides, the eggshell ultrastructural data showed that the total thickness and effective thickness significantly increased (P < 0.05) and mammillary thickness decreased (P < 0.05) in the group of dietary 0.15% Cl compared with the groups of 0.06 and 0.25% Cl. In conclusion, the complete substitution of dietary NaCl by Na₂SO₄ may induce Cl deficiency and depress laying performance and eggshell quality. Na₂SO₄ could partly replace NaCl in diets for laying hens (43–54 wk of age) without adverse effects on performance at the dietary Cl level from 0.10 to 0.25%. Better eggshell quality could be obtained when NaCl was partly replaced by Na₂SO₄ in laying hen diets maintaining Cl level at ∼0.15%.