Rearing conditions during the force-feeding period in male mule ducks and their impact upon stress and welfare

The aim of the first experiment conducted was to further characterise HPA axis func- tionality in male mule ducks during the force-feeding period, by measuring corticosterone levels (Exp. 1). The objectives of the two other experiments were to investigate the impact of different rearing conditions on stress response (Exp. 2) and behaviour patterns (Exp. 3) in male mule ducks. The rearing conditions examined comprised individual (Exps. 1-3) and collective battery cages (Exps. 2, 3), as well as collective floor pens (Exps. 2, 3). The ducks were then fed (Exps. 1-3) by force-feeding for foie gras production or ad libitum (Exp. 1). The highest levels of corticosterone (up to 100 ng·mL −1 ) were measured after initial capture and handling in a large collective rear- ing pen, transfer to a different environment, initial placement in a net for 10 min and injection of 5 µg·kg −1 BW of 1-24 ACTH agonist. Both force-fed and non-force fed male mule ducks responded to a first physical constraint in a net by a large increase in corticosterone levels. Their HPA axis was therefore functional although the effect quickly vanished, which was interpreted as an indication that habituation took place. Most often, corticosterone levels measured before and after force-feeding during the force-feeding period did not differ significantly (P > 0.05) when the ducks were raised in individual cages, even on the first occurrence. A significant increase in corticosterone levels was observed after the first force-fed meal for both groups of ducks raised collectively, i.e. in cages or floor pens, when the practice involved capture and handling. Following the injection of 0.625 and 5 µg·kg −1 BW doses of 1-24 ACTH, cortico-adrenal responses were significantly (P < 0.05) higher and lower for ducks raised in collective floor pens compared to those raised in individual cages, respectively. This hypersensitivity and lower maximal capacity may result from a chronic stressful state related to repeated acute stress (i.e. capture and handling twice daily). Ducks raised in cages (individual or collective) spent more time standing (less lying) and less time inactive i.e. expressing passive behaviour patterns, which suggest that they were not presenting signs of passive coping or learned helplessness. Behaviour observations did not provide any indication of stereotyped be- haviour. From these results, it could have been concluded that placement in individual battery cages