Effects of genetic strain, stocking density, and age on broiler behavior.

Fast growth rate and stocking density are global animal welfare concerns for broiler chickens. The objective of this study was to evaluate the effect of genetic strain and stocking density on the behavior of broilers. In a 2 × 2 randomized complete block design, conventional (CONV) and slow-growing (SG) broilers were stocked at either 29 kg/m (LO, n = 31 birds/pen) or 37 kg/m (HI, n = 40 birds/pen) in 16 pens (n = 4 pens/treatment). On days 25 and 39 (CONV and SG), and 60 (SG only), behavior was observed from video recorded in the morning and afternoon each day. The percentage (%) of all birds in each pen was categorized as either walking, standing, sitting, lateral sitting, eating, drinking, or preening. Two data sets were generated to compare the effect of age (25, 39d) and market body weight (39d CONV, 60d SG). Linear mixed effects models were fitted in R to analyze data. Sitting behavior differed between broiler strains and ages. At 39d, more CONV sat compared to 25d (58.3 % vs 54.5 %, p < 0.0001) and compared to SG at market weight (58.3 % vs 43.9 %, p < 0.0001). CONV broilers sat in a lateral posture more than SG at both ages (5.4 % vs 1.4 %, p < 0.0001) and at market weight (7.4 % vs 0.4 %, p < 0.0001). Standing and walking behaviors were observed more in SG broilers. SG broilers walked more than CONV at 39d and at market weight (2.4 % vs 1.6, p ≤ 0.01). Further, SG broilers stood more than CONV at both ages (11.4 % vs. 7.2 %, p = 0.0004) and market weight (14.9 % vs. 7.1 %, p < 0.0001). While preening behavior did not differ at 25d, more SG broilers preened than CONV at 39d (5.6 % vs 3.9 %, p < 0.0001) and market weight (5.5 % vs 3.3 %, p < 0.0001). LO-stocked broilers preened more at both ages than at HI (5.6 % vs 5.1 %, p = 0.041). These results suggest that conventional broilers exhibit more sitting behaviors, slow-growing broilers exhibit more active behaviors, and chronological and physiological age differences should be considered when making comparisons.