Open-field and tonic immobility responses in broiler chickens administered lycopene

Abstract

The study aimed to evaluate behavioural responses in broiler chickens administered with lycopene and subjected to open field (OF) and tonic immobility (TI) tests. A total of 100 broiler chicks, divided into five groups of 20 chickens each, were used in experiments I and II. Experiment I had control A and lycopene groups, and Experiment II involved control B, habituation (HB), and habituation+lycopene (HB+Lyco) groups. The olive oil or mixed lycopene was administered by oral gavage once daily, commencing at 07:00 h (GMT+1), to each bird for 28 days for Experiment I and 21 days for Experiment II. In Experiment I, the OF test was conducted on days 14 and 28, while in Experiment II, 4-day habituation training was carried out in the HB and HB+Lyco groups from days 17 to 20, followed by the TI test in each of the three groups on day 21. The results of the OF test indicated a reduced (P ˂ 0.05) number of lines crossed, vocalisation, number of jumps, and defecation in the lycopene group compared to control A. An increased (P < 0.05) TI duration was recorded in control B compared to the HB group. Lycopene administration for 21 days increased (P < 0.05) the TI duration value in the HB+Lyco group compared to the HB group. In conclusion, lycopene administration increased fearfulness in broiler chickens, as evidenced by high fear responses during OF and TI tests. This may be due to the decreased ability to habituate to fear-eliciting stimuli in broiler chickens administered lycopene.