On day hens were divided into two

Food Preference Determination
Habituation to Handling, HR Monitor, Runway and Food
Hens were first habituated to human presence and handling (days 1–3), then to moving through the runway in groups (days 3–6) and finally to moving individually (days 6–23), until all hens walked through the tunnel without stopping, hesitating or making distress vocalizations. Habituation to HR monitoring was conducted at the same time as runway habituation and began in groups in a separate room (days 5–15) before continuing individually (days 16–23; as in Davies, Radford, et?al., 2014 and Davies, Nicol, et?al., 2014). Habituation to the food bowl was also conducted in parallel with runway trials, with Z-IETD-FMK fed both the flavoured and standard food in their home groups to ensure the two types were equally familiar (days 14–23).
Test Procedure
Throughout the test period, each hen completed one runway trial twice a day (one in the morning and one in the afternoon) to standardize hunger motivation. All hens were food deprived for 1.5 h in the holding room prior to each trial. Throughout the experiment, hens were tested in the same order, alternating between control and contrast birds. During the preshift phase (trials 1–6), the bowl was filled with 100 g of either flavoured (control group) or standard (contrast group) food (26 g layers mash, 12 g whole wheat, 62 g water). In trial 7, the contrast group was shifted from standard to flavoured food; this feeding regime was retained throughout the postshift phase (trials 8–14).