How does broiler range use impact forage intake, outdoor excretion and gaseous emissions?

International audienceFree range enables broiler chickens to express natural behaviours, eat grass, worms or insects outdoors, but also induces excretion outside the poultry house. To understand how the outdoor run is impacted by range use, we studied three strains of intermediate to slow-growing chickens: JA757 (734 animals, average daily gain (ADG): 36 g/day, outdoor density (OD): 0.26-0.29 chicken/m², rearing duration (RD): 86 days), S757N (735 animals, ADG: 26 g/day, OD: 0.26-0.29 chicken/m² and RD: 100 days) and a dual-purpose (DP) crossbreed (771 animals, ADG: 16 g/day, OD: 0.27- 0.31 chicken/m² and RD: 121 days). Birds had access to a grassy outdoor run with mature trees from 36 days of age. We collected data on the time spent outdoor by broilers using Radio Frequency IDentification (RFID) chips, on the composition and amount of manure and on grass growth to evaluate the impact of range use on grass consumption and outdoor nitrogen (N) / phosphorus (P) excretions. RFID showed that S757N chickens spent about twice as much time outdoor per day than the JA757 and DP ones. Similarly, the S757N chickens also consumed about twice as much grass per day than JA757 and the DP ones. Consistently, S757N chicken outdoor excretions of N and P per day of outdoor access were about twice as much as that of the DP chickens while only about 30% greater than that of JA757. Therefore, we confirmed the relationship between range use and foraging, but we showed strain-dependant outdoor excretion in relation to growth rate and feed intake. A finer understanding of how genetics impact foraging behaviour can help maximize the use of the outdoor run without compromising resource intake and excretion on outdoor areas. The project PPILOW has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N°816172