Roles of limestone particle size ratios and phytase levels to support single-cycled laying hens (60-80 weeks of age) with a focus on production and performance

This study evaluated the role of fine (F) and coarse (C) limestone ratios and exogenous phytase at standard and high levels on performance, egg and bone quality, and inositol levels in single-cycle Hy-Line W-36 hens (60-to-80 weeks of age). A total of 420 hens were randomly assigned into 7 experimental diets in a 2 × 3 + 1 factorial arrangement with 20 replicates of 3 hens per treatment. Factorial treatments consisted of two limestone ratios (40F:60C and 15F:85C) and three Escherichia coli -derived phytase levels (0, 400, and 1500 FTU/kg). The positive control (PC) was an industry standard that consisted of a 40F:60C limestone ratio without phytase and had 4.4 % calcium (Ca) and 0.44 % available phosphorus (avP). A common negative control (NC) diet was created by reducing 0.19 % Ca and 0.17 % avP of the PC. An increase in hen-day egg production (HDEP) was observed with 0 FTU/kg and 40F:60C compared to 15F:85C and a phytase addition dose-dependently increased HDEP for 15F:85C but reduced it for the 40F:60C. Eggshell breaking strength (EBS) increased in 40F:60C with 1500 FTU/kg and 15F:85C with 0 FTU/kg treatments. Additionally, 15F:85C produced more unsaleable eggs compared to 40F:60C. Phytase levels of 400 FTU/kg had a lower gizzard pH and a higher gizzard inositol concentration compared to 0 FTU/kg. This study revealed that 40F:60C with 1500 FTU/kg had benefits on EBS and 15F:85C with 0 FTU/kg caused a decrease in HDEP. Independent of phytase, the group fed 40F:60C limestone particle size produced more saleable eggs.