The two farms used for on-farm assessments were visited once a week in weeks 3, 4, 5, 6 and 7 (week 7 for Redbro broilers only). The same observer performed all behavioural tests and analysed all footage. It was not possible to blind the observer to breed, due to the physical differences between Redbro and Ross 308 broilers. However, detailed scoring systems and a broad range of quantifiable responses (including time and number of birds engaged in an activity) were used to give a thorough assessment of each breed and minimise bias. All video footage was taken using Camileo X-Sports cameras (Toshiba, Surrey, UK) and GeeKam action cameras (Shenzhen Bodalong Technology Co., Ltd, Guangdong, CN) mounted on 1 metre high tripods (AmazonBasics, London, UK).
Broiler behaviour in unenriched areas of the houses was assessed using a combination of scan and focal sampling. Each week, four randomly selected areas of the house that contained no perches or straw bales were video recorded in each house for half an hour simultaneously, giving a total of 2 hours of footage per house per week. Broilers inside a 2 m2 area in front of the camera were scan sampled at 10, 15, 20, 25 and 30 minutes. The number of broilers inside the area was recorded, and they were categorised as either dustbathing, foraging, sitting inactive, sitting pecking, in locomotion (standing or walking), sitting preening, standing preening or other (Table 1). Further to this, of the birds in a seated position, the percentage sitting inactive and the percentage resting were calculated. Focal observations of activity bouts were also conducted to determine how long a broiler remained in activity after standing before returning to a seated position. The first 10 birds to stand after a 10 minute settling period were observed per video, per week, per house (broilers observed N = 710; data for one video were missing (N = 10)). The bird was observed and the time recorded from the time they stood to the time they returned to a seated position. If a bird left the frame then another bird was chosen, although this was not common.
Perch use was assessed using three measures: the number of birds on the perch (perch occupancy), the number and success of any perching attempts, and the time spent perching. All measures were taken using video footage of four randomly chosen perches, from the available seven perches. The perches were recorded for half an hour each, between 12 00 h and 17 00 h, giving a total of 2 hours of video footage per house, per week. For perch occupancy, following a 10 minute settling period the number of birds on the perch was counted during a scan sample every 5 minutes (at 10, 15, 20, 25 and 30 minutes) and an average given for each observation period. After each 5 min scan, the perches were observed for a two minute focal period and all attempts to perch recorded. These attempts were classified as either successful (the broiler alighted on the perch) or failed, and averaged over the observation period. Time spent perching was recorded for the first five broilers to successfully perch following the 10 minute settling period. A perching bout began when the bird landed on the perch and ended when they jumped off the perch. If a broiler fell or jumped off the perch less than 3 seconds after jumping on then another bird was chosen. However, for 48 of the 242 perching bouts observed, the focal broiler was still on the perch at the end of the observation period (when the bird was then disturbed off the perch by the returning observer). The time these birds had been perching for varied (e.g. some had been perching for 20 mins and some for 2 mins). Including the perch times of broilers that had been disturbed soon after they jumped onto the perch may have led to an underestimating of natural perching bout lengths. Therefore, any broiler that had been perching for less than 8 minutes was disregarded. A limit of 8 minutes was chosen as this was the average perch time for broilers that voluntarily left the perch during the observation period (n = 242, M = 466.22 s). In several videos, no or very few Ross 308 broilers jumped onto the perches. Our analysis is therefore assessing the difference in perch time of the subsample of broilers that chose to perch during the observation (Redbro N = 192, Ross 308 = 90).
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