Abstract
Animals in a negative affective state seem to be more sensitive to reward loss, i.e. an unexpected decrease in reward size. The aim of this study was to investigate whether early-life and current enriched vs. barren housing conditions affect the sensitivity to reward loss in pigs using a successive negative contrast test. Pigs (n = 64 from 32 pens) were housed in barren or enriched conditions from birth onwards, and at 7 weeks of age experienced either a switch in housing conditions (from barren to enriched or vice versa) or not. Allotting pigs to the different treatments was balanced for coping style (proactive vs. reactive). One pig per pen was trained to run for a large reward and one for a small reward. Reward loss was introduced for pigs receiving the large reward after 11 days (reward downshift), i.e. from then onwards, they received the small reward. Pigs housed in barren conditions throughout life generally had a lower probability and higher latency to get the reward than other pigs. Proactive pigs ran overall slower than reactive pigs. After the reward downshift, all pigs ran slower. Nevertheless, reward downshift increased the latency and reduced the probability to get to the reward, but only in pigs exposed to barren conditions in early life, which thus were more sensitive to reward loss than pigs from enriched early life housing. In conclusion, barren housed pigs seemed overall less motivated for the reward, and early life housing conditions had long-term effects on the sensitivity to reward loss.
Highlights
The barren housing conditions in which most commercial pigs world-wide are housed limit the expression of important species-specific behaviours, like foraging and exploration (De Jonge et al 1996; Studnitz et al 2007; Wemelsfelder et al 2000), and thereby increase the frequency of manipulative behaviours directed at pen mates, such as ear and tail biting (Beattie et al 2000; Bolhuis et al 2006; Carreras et al 2016)
Pigs that had switched from barren to enriched housing (B1E2) had a higher probability of getting the reward and lower latency to the reward compared to B1B2 pigs housed in barren conditions throughout life (HR 2.48, p < 0.0001, Fig. 3); for the pigs housed in an enriched environment in early life there was no effect of later life housing (E1B2 vs. E1E2)
In the whole test period, both before and after the reward downshift and irrespective of reward size, pigs that were housed barren throughout life had a lower probability and a higher latency to get to the reward than pigs from the other three housing combinations, i.e. enrichment throughout life, enrichment in early life only, or barren housing in early life followed by enrichment
Summary
The barren housing conditions in which most commercial pigs world-wide are housed limit the expression of important species-specific behaviours, like foraging and exploration (De Jonge et al 1996; Studnitz et al 2007; Wemelsfelder et al 2000), and thereby increase the frequency of manipulative behaviours directed at pen mates, such as ear and tail biting (Beattie et al 2000; Bolhuis et al 2006; Carreras et al 2016). Show physiological signs of chronic stress (Beattie et al 2000; Bolhuis et al 2006; Carreras et al 2016) This chronic stress could be linked to a psychological state of (mild) depression. In a SNC test, reward loss is induced by unexpectedly decreasing the reward size or quality for animals that have been trained This may induce a transient, potentially ‘disappointment-like’, aversive affective state, caused by the discrepancy between the anticipated reward, i.e. the reward the animals expected to receive, and the actual reward (Justel et al 2014; Papini 2014; Rosas et al 2007). How aversively the animals respond to such a discrepancy (e.g., depending on the task, by reduced operant responses or a slower speed to get to the reward), has been suggested to be a sign of the animals’ background, longer-term, affective
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
