Effects of Pecking Materials Provision and Edibility on Productivity Indicators in Laying Hens: A Systematic Review...

Feather pecking and cannibalism arise when laying hens' foraging needs are not satisfied, reducing productivity, increasing stress, and elevating mortality. Providing pecking materials is a welfare measure that redirects pecking from conspecifics to the provided material, and this meta-analysis evaluated its effects on productivity and mortality in laying hens. Following the PRISMA guidelines, a systematic search of PubMed, Google Scholar, and ScienceDirect identified 18 articles comprising 24 experiments that examined the effects of pecking materials on body weight (BW), egg production rate (EPR), egg mass (EM), average daily feed intake (ADFI), egg weight (EW), feed conversion ratio (FCR), and mortality (MORT). Risk of bias, assessed using the SYRCLE tool, was generally low to unclear across most domains, though blinding of caregivers was rated as high risk in all studies. A random-effects model was used to pool standardized mean differences (SMD) across studies, and subgroup analysis based on material edibility was conducted through meta-ANOVA to explore potential sources of heterogeneity. Overall, pecking materials provision decreased both BW (SMD = -0.59; 95% CI: [-1.03, -0.14]) and MORT (SMD = -1.10; 95% CI: [-1.79, -0.42]). Subgroup analysis revealed contrasting BW patterns by edibility (edible: decreased; non-edible: increased), whereas MORT decreased consistently regardless of edibility. Publication bias was detected for EPR and ADFI, but trim-and-fill adjustment did not alter the overall conclusions. These findings indicate that pecking materials provision is a useful strategy that reduces mortality without compromising productivity, and suggest that material edibility may partly explain the inconsistent results reported in previous studies. However, given the substantial heterogeneity and unclear risk of bias observed in several domains, further studies incorporating a broader range of material types and rearing conditions are needed to clarify the sources of variability.