文摘
Positive affective states may be as important for animal welfare as the absence of suffering. Thus, there is a need for knowledge of the mechanisms underlying positive affective states, including how they can be induced and assessed. Studies of behaviour during the anticipation of a signalled palatable food reward have been suggested as a promising tool for answering these questions for the following three reasons: Anticipatory behaviour is hypothesized to reflect an appetitive type of positive affective state associated with dopaminergic activity in the brain. Inducing anticipation is useful for inducing pleasure and reducing stress. Finally, anticipatory behaviour can be used to test a subject's sensitivity to reward. However, to test various hypotheses regarding anticipatory behaviour there is a need to develop standardized research protocols. The aim of the present study was to develop and test an automated method for studying anticipatory and consummatory behaviour in laying hens in their home environment based on trace conditioning. Experimental hens (EX) were first trained to acquire the association between CS (conditioned stimulus; a green light) and US (unconditioned stimulus; meal worm) using a trace interval of 3.5 s. To test if EX hens had formed an association between CS and US, they were exposed to CS alone. Then, EX hens were trained to anticipate by gradually increasing the CS–US interval from the initial 3.5 s trace interval with a 1 s increment on every other CS + US presentation up to 22 s after 3 days and 32 s after 5 days of training. Finally, they were tested using a CS–US interval of 22 and 32 s. Control hens (CO) were exposed to CS and US in a random order, and tested as described for the EX hens. The results demonstrated that the EX hens responded to the CS with an increased level of anticipatory behaviour compared to the CO hens, and that this difference between the groups was significant at a CS–US interval of 22 s. No differences between treatments were found in any of the consummatory behaviours. In conclusion, trace classical conditioning can be used for inducing anticipatory behaviour in ad libitum fed laying hens freely moving in the home pen environment. This method will facilitate the testing of hypotheses about reward-related behaviour in laying hens.
