The effect of ketamine on stereotypic behavior in pregnant crated sows

Stereotypic behaviors expressed by captive animals are assumed to be abnormal and are believed to be a symptom of inadequate welfare. Common stereotypies of pregnant sows housed in gestation crates include the oral/nasal/facial (ONF) behaviors of rooting, bar-biting, and vacuum chewing. One hypothesis to explain these behaviors is that crated sows experience poor mental welfare and that ONF stereotypies are a symptom of the depressive condition. The drug ketamine has recently been shown to have rapid and sustained antidepressant effects in humans and animal models of depression. The objective of this study was to assess the effects of an antidepressant treatment in pregnant crated sows. The experiment was a completely randomized design, with two treatment groups and two levels of basal stereotypic behavior performance (high vs. low). Each animal was injected with 0.5 mg/kg body weight of ketamine or saline as control, the antidepressant dose commonly repeated in the literature. Results showed no difference (P > 0.050) in total ONF stereotypic behavior by treatment, although the duration (min/day) of rooting behavior increased (P = 0.020) in the ketamine-treated sows with basally high levels of ONF behavior. Piglets from these sows also weighed less (P = 0.025) at weaning than piglets from all other sows. In all, these results do not conclusively suggest that ONF stereotypic behavior performance by crated sows is a symptom of depression, however further research is needed to fully understand the increase in rooting behavior and decrease in piglet weaning weight observed in high stereotyping sows after ketamine treatment.