Effect of Feed Restriction on the Behaviour and Welfare of Broiler Chickens

SIMPLE SUMMARY: Commercial genotypes of broiler chickens reared for meat purposes in intensive rearing systems are selected for fast growth and high breast yield and kept under conditions that may negatively affect normal behavioural patterns and reduce activity levels. Besides, quantitative feed restriction, used in the field to manipulate chicken growth and improve feed efficiency, may produce hunger and abnormal behaviours. Under these conditions, health and welfare are at risk. Thus, the present study aimed to evaluate the effect of genotype, sex and feed restriction on the welfare of broiler chickens by examining behaviour and corticosterone as a stress indicator during the production cycle. Results showed that behavioural differences between two fast-growing genotypes were limited in quantity and quality, whereas sex and age played a major role. The effect of sex was related especially to size so that heavier males were more active at earlier ages but moved less towards the end of the trial when their walking ability/comfort decreased. Feed restriction stimulated activity during and beyond the restriction phase without relevant effect on stress condition as measured by the plasma and faeces corticosterone. ABSTRACT: Under intensive rearing conditions, the welfare of broiler chickens may be at risk depending on genotype and sex, due to their different growth rates. The practice of quantitative feed restriction may also impact on welfare. This study aimed to evaluate behaviour and corticosterone content in plasma and faeces at different ages using 896 one-day-old chicks housed in 32 pens, allocated to 8 groups, i.e., 2 genotypes (standard vs. high breast yield) × 2 sex × 2 feeding plans (ad libitum vs. restricted, AL vs. FR). The feeding system affected the percentage of standing (9.84% vs. 11.7% in AL vs. FR; p ≤ 0.001), feeding (7.51% vs. 8.17%; p ≤ 0.01) and sitting/lying (67.0% vs. 64.1%; p ≤ 0.001), and the faeces corticosterone content (12.2 vs. 13.6 ng/g in AL vs. FR; p ≤ 0.10). Sex affected the percentage of pecking other chickens, standing and comfort behaviours. Changes in behaviour were recorded between high and standard breast yield genotypes with faeces corticosterone which tended to be higher in the former (p ≤ 0.10). Significant interactions between the main factors and age were observed. Major changes in behaviour were due to feed restriction, which stimulated activity during restriction.