Assessing transient affective state of broiler chickens using intracranial LFP recordings

Abstract

When broiler chickens reach their target weight (~5-8 weeks-old), they experience a number of pre-slaughter processes such as capture, transport and lairage. The impact of these processes on broiler welfare could be substantial. This project aims to provide a new method for measuring broiler welfare by using intracranial LFP recordings in three key brain areas: the nidopallium caudolaterale (NCL, medial prefrontal cortex analogue), nucleus taeniae (TnA, medial amygdala homologue) and the hippocampal formation (HF, hippocampus homologue). Broilers were stereotaxically implanted with recording electrodes across two studies. Study one targeted the NCL and TnA, and study two targeted the TnA and the HF. Additionally, behaviour was recorded in both studies and heart rate and peripheral body temperature were recorded during study two. During a seven-day experimental period, broilers were exposed to four conditions (inversion, isolation, comb pinch or treat food) twice a day, according to a semi-randomised schedule. During the testing period, broilers were fitted with a wireless logger to store local field potential data. In all three brain areas, theta and alpha power decreased from baseline levels during all conditions, however, the most marked decrease often occurred when the experimenter entered/left the room or approached the pen. Heart rate did not deviate from baseline levels during isolation, but increased during the other conditions. Overall changes in theta and alpha power relative to baseline likely reflected arousal, rather than the valence of the conditions experienced, which is supported by behavioural changes. Coherence between the TnA-TnA, HF-HF and TnA-HF in the theta and alpha bands was significantly higher than at baseline when mealworms were presented. This increase in coherence was significantly different from the changes in coherence during the negatively-valenced conditions (inversion, isolation and pinch). Changes in coherence between these brain areas may thus dissociate between the experience of positive and negative affective states in broiler chickens.