LAUSR

The present study was conducted to investigate the effect of dietary supplementation of organic acids (OA) on performance and phytate phosphorus utilization in laying hens fed diets with different non-phytate phosphorus (NPP) levels. A total of 240 Hy-Line W-36 laying hens, 32-wk-old, were randomly allocated into the 8 dietary treatments with 5 cage replicates of 6 birds each. The main trial period lasted for 10 wk (34–44 wk of age), following a 2 wk adaptation period (32–34 wk of age). Dietary treatments consisted of a 4 × 2 factorial arrangement of treatments, including 4 supplemental OA (control, citric, butyric, or fumaric acids, 5 g/kg of diet) and 2 different NPP levels (60 or 100% of Hy-Line W-36 recommended values). Results showed that dietary OA supplementation increased (P < 0.05) egg production percentage, with the greatest values assigned to the hens fed citric and butyric acids-supplemented diets. Reducing dietary NPP level resulted in a marked decrease in egg production in control hens, while OA supplementation of the NPP-deficient diet could maintain egg production and egg mass, resulted in the significant (P < 0.05) OA × NPP interactions. Although feed intake was not affected by dietary treatments, supplemental OA improved (P < 0.05) feed conversion ratio in NPP-deficient hens (OA × NPP, P < 0.05). Dietary OA supplementation increased (P < 0.05) eggshell thickness; however, it had no marked impact on shell breaking strength. Serum lipid metabolites were influenced by dietary OA supplementation, so that supplemental OA decreased (P < 0.01) serum cholesterol level and increased (P < 0.001) serum high-density lipoproteins. Feeding the NPP-deficient diet decreased (P < 0.01) tibia ash and increased (P < 0.001) serum alkaline phosphatase activity. On the other hand, dietary supplementation of fumaric acid increased (P < 0.01) tibial ash and Ca contents compared to the control hens. Tibia P content was lower (P < 0.05) in hens fed the NPP-sufficient diet. Inclusion of citric acid into the NPP-deficient diet increased tibia P, resulted in a significant (P < 0.001) OA × NPP interaction. Dietary supplementation of OA reduced (P < 0.01) ileal enumeration of Salmonella, and the lowest (P < 0.05) Escherichia coli count was observed for hens supplemented with butyric acid. The present findings indicate that dietary OA supplementation can increase egg production, egg mass, and eggshell thickness in hens fed the NPP-deficient diet. The beneficial impact of citric acid on tibia P content of NPP-deficient hens suggests that supplemental OA could improve P utilization even in young laying hens.