Acute and chronic stress in post-weaned pigs increases the detection threshold for sucrose solutions. Anhedonia in nursery pigs. Effect of acute and chronic stress over the detection threshold for sucrose solutions

Please note: Changes made as a result of publishing processes such as copy-editing, formatting and page numbers may not be reflected in this version. For the definitive version of this publication, please refer to the published source. You are advised to consult the publisher's version if you wish to cite this paper. Abstract Hedonism during intake is affected not only by food or solution characteristics but by animal's stress that has been reported to reduce the ability to experiment pleasure in front of palatable solutions in rats and humans. However, little information is known about anhedonia process in productive animals like pigs. To assess whether pigs could change their preferences for hedonic solutions due to stress situations we performed 3 consecutive experiments. Pigs (42d-old) were randomly allocated in two groups in each experiment: SG (stressed group) and CG (control group). SG pigs were exposed to an acute stress during 2 consecutive days by mixing animals of contiguous pens during 20 minutes (Experiment 1), subjected to movement restriction by immobilization for a 3-min period, 3 times a day for 3 consecutive days (Experiment 2) or were leave to their weaning process known to be a stressful factor itself. The ability to detect sucrose solutions in both groups were measured after the stress protocols of each experiment. Animals were tested in pairs (12 control pairs and 12 experimental pairs) to prefer water vs. sucrose (0.5 or 1%) solutions during 30 min. In experiments 1 and 2 control pigs showed higher intakes of 0.5% and 1% sucrose solutions over water during the choice tests. SG pigs did not show any difference between solutions intakes of sucrose 0.5% and water. However, at higher sucrose inclusion (1%) they clearly preferred sucrose. Results of experiment 3 were not consistent with anhedonia described in literature and stressed animals preferred both sucrose inclusions. Results shows that stress in pigs may increase their detection threshold to detect low concentrations of sucrose under specific stressful situations probably because of their impaired ability to experience pleasure as a result of a hedonic stimulus. However, preference for intense sweetness could be more pronounced in stressed animals due to their rewarding deficit.