Tickling and its effects on the affective states of laying hens

Human-animal interactions may significantly influence the productivity and welfare of animals in the livestock industry. The nature of manipulation influences the physiology and behaviour of animals positively or negatively. To improve animal welfare, it is important to not only reduce unwanted negative states (fear, pain, suffering) but also to induce positive affective states in animals. Tickling has been described in multiple studies to evoke positive affective states in rats. We tested whether a similar form of tactile stimulation induces changes in the valence of affective states of laying hens using an operant judgement bias test. Sixteen laying hens housed in deep litter pens were divided into two groups with different forms of manipulation: a handled group (n = 8) or a tickled group (n = 8). First, the animals were trained to discriminate between the positive (PS, pecks rewarded with mealworms) and negative stimuli (NS, pecks punished with white noise) in a visual discrimination task (Go/NoGo). They were then subjected to the judgement bias test, in which responses to PS, NS and ambiguous middle stimulus (MS) were recorded. All hens successfully learned to discriminate between PS and NS. The treatment did not induce changes in judgement bias test performance. Tickling in the manner we administered it and applied in adulthood, did not appear to be perceived by hens as a positive event. The treatment did not affect judgement because the behavioural assay was not sensitive enough to detect a possible effect, or chickens did not find the tickling as administered to be positive enough. Perhaps the other more playful interactions with hens, a larger dosage or the treatment at an early period of life could have greater impact.