Genetic parameters and genomic prediction accuracy for piling behaviour using individual-level computer-vision data from ArUco-marked laying hens

Background Recurring piling, a detrimental behaviour in laying hens where birds cluster densely, leads to heat stress, injuries, and potentially smothering. While its occurrence is a major concern in large group housing systems for laying hens, the causes are poorly understood, and management interventions have shown variable success. Line differences suggest a genetic predisposition, but the absence of individual-level phenotypic data has, until now, prevented a formal genetic analysis. This study aimed to estimate, for the first time, the genetic parameters and genomic breeding values of piling behaviour in laying hens. Results We monitored 1,441 genotyped Dekalb White hens at 40 weeks of age in a semi‑industrial facility over nine days. Individual participation in 115 piling events was recorded using automated video tracking with ArUco markers. Three traits were defined: overall participation in piles (OSI; binary), event-specific participation (OSE; binary), and a continuous rank score based on joining order (RSE). Genomic relationship matrices were used to estimate variance components, heritability, and prediction accuracy. Significant genetic variance was found for all traits. Heritability estimates on the observed scale were low to moderate: 0.11 for OSI, 0.05 for OSE, and 0.05 for RSE. Cross‑validation accuracies of genomic breeding values ranged from 0.27 to 0.44. Selection against the lowest 10% of estimated breeding values was predicted to reduce trait expression by 21–42%, indicating good opportunities for genetic improvement. Genetic correlations among traits were high (point estimates > 0.99). The most accurate genomic predictions were obtained by using event‑level data (OSE) to predict the overall propensity to pile (OSI). Conclusions This study provides the first evidence that piling behaviour in laying hens is a heritable trait. The significant genetic variance and predicted response to selection across traits confirm the potential for piling mitigation through genetic selection. A practical strategy for breeding programs could involve selecting against the overall propensity to pile (OSI) using event-level participation data (OSE). These findings open a new avenue for mitigating piling through breeding.