The response of laying hen production, performance, bone health, and inositol levels to limestone particle size ratios and phytase levels supplemented during the post-peak period (40-60 weeks of age)

As hens age, egg production and quality decline. Producers are interested in extending the production of their hens to help with production costs and demand. The objective of this study was to investigate the role of the ratio of fine (F) and coarse (C) limestone and exogenous phytase at standard and superdosing levels on performance and egg quality of post-peak hens from 40-60 weeks of age. A total of 560 Hy-Line W-36 hens (20 replicates of 4 hens per treatment) were randomly assigned into 7 experimental diets in a 2 × 3 + 1 factorial arrangement. The positive control (PC) was formulated to an industry standard that consisted of a 40F:60C limestone ratio without phytase and contained 4.4% calcium (Ca) and 0.44% available phosphorus (avP) for both layer 2 and layer 3 diets. A common negative control (NC) diet was created by reducing Ca and avP by 0.19% and 0.17% respectively compared with the PC. The factorial treatments consisted of two limestone ratios (40F:60C and 15F:85C) and three E. coli-derived phytase levels (0, 400, and 1500 FTU/kg) formulated from the NC. Results indicated that 40F:60C at 0 and 400 FTU/kg increased hen-day egg production (HDEP). Limestone ratios of 15F:85C decreased feed intake (FI), increased both eggshell thickness (ST) and weight (SW), but also increased unsaleable eggs (UE) compared to 40F:60C. Additionally, 0 and 400 FTU/kg increased egg quality parameters such as Haugh unit (HU) and albumen height (AH) but 1500 FTU/kg increased inositol phosphate breakdown as well as bone quality.