Shoreh Miller, D.V.M., Ph.D., DACLAM
Robert Wood Johnson Medical School, UMDNJ

In this review, swine behavior and various methods of enrichment are discussed. The review is based on both published journal articles and anecdotal successful enrichment methods that were shared recently on CompMed Listserve (AALAS.org).

Animal Model
For the past two decades, swine have been used with increasing frequency in biomedical research as models of human disease, based on notable anatomy and physiology similarities to humans. These studies include cardiovascular research, nutrition, organ transplantation, surgical training and plastic surgery. (Stanton and Mersmann, 1986; Swindle, 1992; Tumbleson, 1986).

Swine Behavior
Swine are omnivorous, and use their strong snouts for rooting in the soil. Rooting, foraging and social living are extremely important behaviors. Swine are diurnal, with elevated activity during the evening. In the laboratory, swine activity is related to the presence and activity of humans, rather than the light-dark cycle. Laboratory swine spend 70-80% of their time lying down or sleeping unless it is feeding time or people enter the room.

Swine are extremely intelligent animals with excellent memories. They can be trained to walk out of their cages and be guided. They are relatively insensitive to noise and are themselves very noisy; however, sudden, extremely loud noises frighten them. Responses to acute stressors are vocalization and attempts to escape. (Swindle et al, 1994, Smith and Swindle 2006).

Swine naturally form close-knit groups and become distressed when separated from other group members, even for short periods of time. Sows and juveniles must be housed in harmonious social groups. Aggression is expressed by butting or biting the neck and ears and quickly subsides in a stable social group.

When unfamiliar swine are housed together, they must be carefully monitored until the dominance hierarchy is established. Incompatible animals will fight and dominant animals may severely injure others in the pen, especially during feeding time. If subordinate individuals are separated from the group, they will be attacked upon reintroduction, whereas a dominant animal can be separated and reintroduced without incident (Bollen et al, 2000). Because adult boars are solitary, individual housing is appropriate. Barrows (castrated males) may be group housed using the same guidelines that are used for females. (Smith and Swindle, 2006).

Toys and food treats used for rooting and foraging, social housing and interactions with humans are among major tools for swine enrichment. In a recent online CompMed Listserve survey, 27 responders shared their methods of choice for swine enrichment. A summary of the responses are presented below.

Toys
Ideal toys must be contaminant-free, durable and cage washer safe.  Hanging toys satisfy the need to chew and rub, and items on the floor may be used for rooting. Effective sanitization is essential for all enrichment toys because swine will avoid them if they become soiled. Large durable balls made of impervious materials such as “Big Red Apple” (figures 1 and 2), Jingle balls, and Dumbbells provide opportunity for rooting. Hanging chains with various objects attached across the top of the pen and chewy toys such as Kong toys hanging or on the floor satisfy pigs’ rooting, mouthing and chewing behavior. The hanging toys should be hung low—almost touching the ground—because swine like their heads down in rooting position. Swine also enjoy stainless steel mirrors and rattles. The novelty of toys is key to ensuring a swine’s continued interest; therefore, toys should be rotated regularly. Swine also like to chew flexible objects (figure 3) made of rubber.

Foraging
A substrate such as straw, wood chippings or wood shavings containing commercial foraging pellets, grains or cut fruits will satisfy pigs’ foraging and rooting needs. Also, a durable rubber ball with holes for treat insertions will provoke rooting and foraging Traffic cones with food such as marshmallows or dried fruit hidden at the cone apex are also useful enrichment toys. Cones need to be replaced after 1-2 months.

Social Housing
Social housing with compatible animals is essential for swine. If for scientific, cage size or veterinary reasons, individual housing is necessary, swine should have sensory contacts such as visual, smelling or touching noses through the walls of the pen.

Auditory
Natural sound, classical and easy listening music can be used for swine enrichment.

Human Interaction
The influence of humans on swine behavior in a laboratory setting is very significant. Swine that are routinely allowed to approach humans, and rewarded by patting and scratching, will be calmer and less stressed during research procedures. Positive interactions with humans—along with a food treat—can be used for physical examination or drug dosing.

Movies
Children’s movies, including “Babe,” may appeal to swine. A television should be placed at swine head height, as swine cannot look up.

Food Treats
Food treats can be used as training rewards or for foraging. Favorite treats include apples, bananas, air popped popcorn, sweet potatoes, carrots, pears, grapes, frozen juice, snow cones (pigcicles) or ice cubes, cookie dough for hiding medication inside (use sparingly), yogurt, crushed rodent or rabbit chow, Timothy Hay Mini Bales and commercially available treats.

Scratching
Swine enjoy being scratched either by a scratching board or by humans. The scratching board can be placed to the side of the pen; swine, however, prefer to be scratched by people.

References
1. Smith, A.C. and Swindle, M.M., 2006. Preparation of Swine for the Laboratory. ILAR, 47:4, pp. 358-363.

2. Swindle, M.M., Smith, A. C., Kathy Laber-Laird, K., and Dungan, L. 1994. Farm Animals in Biomedical Research—Part One, Swine in Biomedical Research: Management and Models. ILAR, 36: 1., pp 1-5.

3.  Bollen, P.J.A., Hansen, A.K., and Rasmussen. 2000. The Laboratory Swine. Boca Raton, CRC Press.

4. Stanton HC, Mersmann HJ, eds. 1986. Swine in Cardiovascular Research. Vol 1-2. Boca Raton: CRC Press.

5.  Swindle MM, ed. 1992. Swine as Models in Biomedical Research. Ames: Iowa State University Press.

6. Tumbleson ME, ed. 1986. Swine in Biomedical Research. Vol 1-3. New York: Plenum Press.

7.  http://www.bio-serv.com/Swine_Enrichment_Treats/F5136.html

8.  http://www.rspca.org.uk/sciencegroup/researchanimals/ethicalreview/housingandcare

Acknowledgement
The author would like to thank Bio-Serv of Frenchtown, New Jersey for the photographs used in this article.

The Enrichment Record Issue 6

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