Effect of feeding system, genotype and gender on behaviour and stress in broiler chickens

The present study aimed at evaluating whether and how behaviour and stress of broiler chickens could be affected by genotype (standard vs. high breast yield), sex, and feeding regime (ad libitum vs. restricted rate, 80% from 13 to 21 d of age). A total of 768 day-old chicks was housed in 32 pens, their behaviour was video- recorded at 11, 18, 25, 32, 39 and 45 d of age, and controlled for 10 consecutive seconds every 30 min to measure the percentage of chickens showing mutually exclusive behaviours (standing, sitting/lying, walk, drink, feed, peck floor, peck fixture, peck tail of other bird, peck other bird, peck own tail, dust bath). Faeces pooled by pen and individual plasma were weekly sampled to measure corticosterone concentrations by microtitre radioimmunoassay (RIA). Behavioural and corticosterone data were analysed with PROC GLIMMIX and MIXED (SAS Institute, Cary, USA), respectively, including genotype, gender, feeding regime and age as fixed effects, and pen as a random effect. On the whole trial, genotype affected the percentage of standing chickens (11.1% vs. 12.3% in standard vs. high breast yield; P<0.001). Males were observed pecking other birds more than females (0.11% vs. 0.05%; P<0.001) and showed less comfort activities (6.21% vs. 6.51%; P=0.05). Broilers submitted to feed restriction were more active than those fed ad libitum (standing birds: 12.5% vs. 10.8% ; P< 0.001), were more often at the feeders (9.19% vs. 8.20%; P=0.01), and showed higher faecal corticosterone (13.6 ng/g vs. 12.2 ng/g; P<0.10). In conclusion, feed restriction promoted broiler activity, but chickens experienced hunger and stress (as measured by corticosterone concentrations), whereas the other factors had a weak effect. Relatively to stress measurements, corticosterone in plasma was not affected, whereas pooled faeces collected from the litter appeared to be a valid matrix, to be sampled in a repeated, non- invasive, and non- stressful way.