Pecking block use at individual level is associated with improved eggshell quality and keel fractures in laying hens

Laying hens possess a calcium-specific appetite that intensifies towards lights out to meet the high demands for eggshell formation and skeletal maintenance. Pecking blocks (PBs) are edible enrichments that can serve as an additional calcium source. We explored the relationships between PB preference (PBp), PB use, keel fracture status (KS), and eggshell quality. One hundred and twenty Dekalb White and 120 Bovans Brown were housed in twelve enriched cages. Three types of PB differing in calcium and grain content were offered in a series of paired preference tests over three 4-week periods in phase 1 of the study (26 to 39 WOA). This was repeated in phase 2 (41 to 48 WOA), with three 2-week periods. Block pecking behavior was measured at the individual level by live observations of 7 focal birds per cage (n = 77) once weekly (3-time intervals). Relative PBp was based on the frequency of pecks calculated as preference ratio between PBs. Hens were categorized as PB "users" or "nonusers" based on the number of pecks at all blocks throughout the experiment. After each period, hens with PBp were isolated for egg collection. The egg weight (EW in g), shell breaking strength (SBS in kg force), and shell thickness (ST in mm) were analyzed. Using radiography, we scored keel fractures at 40 WOA (baseline) and after each period in phase 2. Consistency of hen's PBp between phases was determined using kappa analysis and indicated moderate agreement (kappa = 0.6). PBp had no association with KS (p = 0.36), EW(p = 0.64), and SBS (p = 0.68). However, block "users" maintained ST over time (p = 0.002) and had higher SBS (p = 0.009) compared to "nonusers." Hens who experienced a new keel fracture during phase 2 (n = 11) increased pecking in phase 2 compared to phase 1 (p= 0.023) and pecked more than hens without a keel fracture in phase 2 (n = 11; p= 0.006). This study suggests that individual hens' use of pecking blocks may reflect individual calcium demand for eggshell formation and bone repair.