Vietnamese potbellied miniature pigs were introduced to the United States in the early 1980s and were promoted as a household pet by emphasis on their small size, clean habits, and reputed intelligence. Initially, the population was small, reflecting a high purchase price. As their numbers increased, their price declined so that now they are inexpensive and easily acquired. The number of miniature pet pigs presently living in the United States is unknown. The prevalence of breed associations and pet pig information sites on the Internet suggests that they are still popular, and companion animal veterinarians are occasionally consulted about medical care and husbandry problems. Behavior problems, especially those dealing with aggression toward the owners, are another area in which companion animal veterinarians may be consulted. Pet pigs are relinquished to rescue groups for a variety of reasons, including the pig grew larger than expected; zoning restrictions; and behavior problems, especially aggression towards humans.1,2 Although much research has been conducted on intraspecies aggression in commercial swine, no research has been reported on the prevalence or determinants of aggression directed towards humans, to our knowledge. This is not surprising because prior to the introduction of potbellied pigs, swine in the United States rarely lived in people's homes or in direct contact with humans. Because swine social behavior differs from that of other domesticated animals, it is not feasible to extrapolate from what is known about human-directed aggression in dogs, cats, and horses and apply it to swine. Pigs frequently have aggressive behaviors towards other pigs in the form of threatening head gestures, pushing, shoving, snapping, and biting.3,4 Pigs are born with fully erupted deciduous canine teeth used to aggressively compete with littermates for access to productive teats of the sow.5–8 Mixing of unfamiliar pigs invariably involves aggressive behavior, and although this decreases within 24 hours as the pigs establish a social hierarchy,8 threats still occur between dominant and subordinate pigs.9
To collect data on human-directed aggression, inhome observations or personal interviews of owners of pet pigs were not feasible, and it was decided that an Internet survey that used strict inclusion criteria would be the most appropriate method of collecting data from a large number of owners of pet pigs. Internet surveys have been used to collect data for research on several topics of veterinary medical interest.10–12 Internet methodology can provide access to samples and computerized processing of data that far exceeds that possible by more traditional techniques. In a recent review, the preconceptions that have been raised about limitations of Internet surveys were examined and the authors concluded that the data and findings provided by Internet methods are, at least, as good in quality as data and findings provided by traditional methods.13
The main disadvantage of Internet-collected data about the behavior of companion animals is that one is relying on observations of the animal owners. This is a problem in companion animal behavior research regardless of whether one is dealing with clinical interviews with pet owners, telephone interviews, or Internet methodology. Internet studies are known to involve participants who are self-selected for the topic of interest. Because we were interested in responses from pet pig owners who were particularly interested in pig behavior and motivated enough to return an Internet survey, this self-selection was considered an advantage. However, interest in aggressive behavior was disguised, and no mention was made of enrollment criteria, so as to not influence responses.
Given that human-directed aggression is both a public health issue and a reason for relinquishment of pet pigs, this study was undertaken to determine associations between sex, neutering status, age of weaning, presence of conspecifics (other pet pigs), or environmental enrichment and human-directed aggression in miniature pet pigs.
Lord LK, Wittum TE. Survey of humane organizations and slaughter plants regarding experiences with Vietnamese potbellied pigs. J Am Vet Med Assoc 1997;211:562–565.
Fraser D, Kramer DL, Pajor EA, et al. Conflict and cooperation: sociobiological principles and the behaviour of pigs. Appl Anim Behav Sci 1995;44:139–157.
Hemsworth PH, Winfield CG, Mullaney PD. A study of the development of the teat order in piglets. Appl Anim Ethol 1976;12:225–233.
Meese GB, Ewbank R. The establishment and nature of the dominance hierarchy in the domesticated pig. Anim Behav 1973;21:326–334.
Gobar GM, Kass PH. World Wide Web–based survey of vaccination practices, postvaccinal reactions, and vaccine site–associated sarcomas in cats. J Am Vet Med Assoc 2002;220:1477–1482.
Jehn CT, Perzak DE, Cook JL, et al. Usefulness, completeness, and accuracy of Web sites providing information on osteoarthritis in dogs. J Am Vet Med Assoc 2003;223:1272–1275.
Steiner A. Delegation of castration of calves and lambs to the livestock owner: internet survey of members of the Swiss Association for Ruminant Medicine. Schweiz Arch Tierheilkd 2003;145:273–282.
Gosling SD, Vazire S, Srivastava S. Should we trust web-based studies? A comparative analysis of six preconceptions about internet questionaires. Am Psychol 2004;59:93–104.
Miniature pet pig behavior survey. Available at: http://intercom.virginia.edu/SurveySuite/Surveys/petpigs. Accessed January 3, 2007.
Siegal S, Castellan NJ. Nonparametric statistics for the behavioral sciences. 2nd ed. Boston: McGraw-Hill Book Co, 1998;111–124.
Kanitz E, Tuchscherer M, Puppe B, et al. Consequences of repeated early isolation in domestic piglets (Sus scrofa) on their behavioural, neuroendocrine, and immunological responses. Brain Behav Immun 2004;18:35–45.
Ruis MAW, te Brake JHA, Engel B, et al. Adaptation to social isolation: acute and long-term stress responses of growing gilts with different coping characteristics. Physiol Behav 2001;73:541–551.
Hart BL, Eckstein RA. The role of gonadal hormones in the occurrence of objectionable behaviours in dogs and cats. Appl Anim Behav Sci 1997;52:331–334.
D'Eath RB, Lawrence AB. Early life predictors of the development of aggressive behaviour in the domestic pig. Anim Behav 2004;67:501–509.
Giersing M, Andersson A. How does former acquaintance affect aggressive behaviour in repeatedly mixed male and female pigs? Appl Anim Behav Sci 1998;59:297–306.
Mason SP, Jarvis S, Lawrence AB. Individual differences in responses of piglets to weaning at different ages. Appl Anim Behav Sci 2003;80:117–132.
Worobec EK, Duncan IJH, Widowski TM. The effects of weaning at 7, 14 and 28 days on piglet behavior. Appl Anim Behav Sci 1999;62:173–182.
de Jong IC, Prelle IT, van de Burgwal JA, et al. Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs. Physiol Behav 2000;68:571–578.
De Jonge FH, Bokkers EAM, Schouten WGP, et al. Rearing piglets in a poor environment: developmental aspects of social stress in pigs. Physiol Behav 1996;60:389–396.