Association between vent pecking and fluctuating asymmetry, heterophil to lymphocyte ratio, and tonic immobility duration in chickens

The purpose of the present study was to analyze the relationship between incidence of vent pecking, fluctuating asymmetry, heterophil to lymphocyte ratio, and tonic immobility duration in chickens. The experiment (140 birds in three different replicates) measured the fluctuating asymmetry of several traits (middle toe length, leg length, wing length, wattle length, and leg width), the heterophil to lymphocyte ratio, and the tonic immobility duration in 20-week-old pullets of five Spanish breeds of chickens (Blue Andaluza, Quail Castellana, White-faced Spanish, Red-barred Vasca, and Birchen Leonesa), and a White Leghorn population, with and without evidence of suffering from vent pecking. The number of birds per breed was 20, 24, 12, 20, 18, and 46, respectively. There was a significant difference between vent pecked and non-vent pecked birds on the relative fluctuating asymmetry of middle toe length (P <0.05), the relative fluctuating asymmetry of birds who suffered from vent pecking being larger. The combined relative fluctuating asymmetry of the five traits approached levels of statistical significance (P =0.08). There was a significant difference (P <0.001) in heterophil to lymphocyte ratio and tonic immobility duration between vent pecked and non-vent pecked birds, the ratio being higher and the duration being longer in the group of birds that suffered from vent pecking. Thus, vent pecked birds were more asymmetrical, stressed and fearful than non-vent pecked birds, having increased relative fluctuating asymmetry, heterophil to lymphocyte ratio and tonic immobility duration. Differences were consistent across the breeds. Results indicate that vent pecking is associated with other measures of stress e.g. fluctuating asymmetry, heterophil to lymphocyte ratio, and tonic immobility duration.