Effects of Stress and Balance of Options on Decision-Making and Associated Physiological Responses in Laying Hens
Animal preferences in choice tests have frequently been used within animal welfare research to make recommendations about animal handling and husbandry. It is therefore important that these results are obtained in a way that, as far as possible, respects the behavioural capabilities of the animal. Stress has been shown to affect cognitive processes in animals and could therefore affect the decision making process. To examine the effects of stress on decision making, 16 laying hens were trained to distinguish between two different quantities of a food reward. A decision balance point was found, by increasing the cost of reaching the large reward, in lines with the theory of demand curves. Hens were then tested in a t-maze choice test with both balanced and unbalanced sets of options, with and without prior stress treatment. Choice, latency to choose, heart rate and temperatures were recorded. Hens that received stress treatment prior to their first test session were affected by this even in subsequent sessions where they did not receive stress treatment. This effect was not found in hens that first received stress treatment prior to their second test session. This shows the influence of previous experiences on animal decision making. Also, a decrease in heart rate during the decision making period was found, when making a choice between balanced options, indicating anticipation of difficulty. Additionally, this shows that physiological measurements such as heart rate could be of importance for future studies and greater understanding of underlying processes of animal decision making.
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