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United States Department of Agriculture

Agricultural Research Service

Research Project: SAFEGUARDING WELL-BEING OF FOOD PRODUCING ANIMALS Title: Does the presence of a human effect the preference of enrichment items in young, isolated pigs?

item Deboer, Shelly -
item Garner, Joseph -
item Lay, Jr, Donald
item Eicher, Susan
item Lucas, Jeffrey -
item Marchant-Forde, Jeremy

Submitted to: Applied Animal Behaviour Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2012
Publication Date: January 1, 2013
Citation: DeBoer, S.P., Garner, J.P., Lay Jr., D.C., Eicher, S.D., Lucas, J.R., Marchant Forde, J.N. 2013. Does the presence of a human effect the preference of enrichment items in young, isolated pigs? Applied Animal Behaviour Science. 143:96-103.

Interpretive Summary: The domestic pig is becoming increasingly used as a laboratory animal due to anatomical and physiological similarities with humans. Both within a laboratory setting, and in intensive commercial farming, the pig is often housed in a barren environment and also may be kept in an individual enclosure. Within the laboratory, isolation may also be practiced. As an animal which has evolved to be social and highly active within a complex environment, the types of housing systems in which they are kept may impose stress. Our experiment was designed to examine different ways to improve or enrich the environment and to have the pig tell us which it preferred by seeing which enrichments it would spend more time with. We offered the pig choice between 4 different pens; one pen was a standard rectangular pen with metal floor and solid sides (CTRL), one pen had a rubber mat on part of the floor (MAT), one pen had a mirror on one wall (MIR) and one pen had a barred gate instead of a wall through which it could see another pig across a passageway (COM). We found that pigs preferred to spend significantly more time in the COM pen compared to the CTRL pen, with the other pens intermediate. We then re-examined the data to see if the preference changed when a human was in the room and found that when the human was present, the pigs spent much more time in one of the social-type pens (COM or MIR) compared to when the human was absent. Within the social pen category, COM or MIR were equally chosen. These results show that the pig's choice was affected by changes in the experimental setting. When undisturbed, the pigs clearly chose to spend more time across from the other pig, which could lead us to conclude that only that enrichment was important. However, when the human entered the room, the choice shifted and the mirror became as important as the other pig. The reflection of the pig in the mirror may be perceived as a closer companion pig but more research would be needed to confirm this. However, it could be that a mirror is a useful way of improving a pig's ability to cope with stressful situations in environments in which they have to be housed alone.

Technical Abstract: Pigs may be housed individually in both production and research settings. Gregarious by nature, pigs kept in isolation may show behavioral and physiological signs of stress. In this study we investigated the preference of individually-housed pigs, for social and non-social enrichments. Three enrichment items were compared: a mat on part of a woven wire floor (MAT), a companion visible across the passageway (COM) and a mirror on one wall (MIR). Fourteen weaner pigs (Yorkshire × Landrace) were housed individually with continuous access to 4 adjacent pens, 3 of them containing one enrichment and one control (CTRL) pen with no enrichment. Pigs spent more time (p<0.05) in the COM pen compared to the CTRL pen with the MAT pen and the MIR pen as intermediates. Additionally, investigative and inactive behaviors were performed more in the COM pen compared to the CTRL pen (p<0.001). A second analysis was performed on the data to investigate changes in preferences in the presence or absence of a human in the room. The pens were then combined into 2 categories: social pens (COM and MIR) and nonsocial pens (MAT and CTRL). The probability of a pig choosing a social pen when a human was present was significantly higher (p<0.001), then when absent. Within the social enrichments, the probability of the animal choosing either MIR or COM was not different (P>0.05). Our results confirm that preference studies are highly sensitive to experimental conditions and the assumption that the most important preference is the one the animal spends most of its time with can be misleading. It appears that a mirror may be used by the animal for social support during periods of perceived stress, however further investigation is warranted.

Last Modified: 12/19/2014