24 Effects of Oral Supplementation of Cannabidiol on Young Stallion Behavior

Abstract Cannabidiol (CBD) has become a popular product in the recent months due to change in legislation with the passing of the Agricultural Improvement Act in 2018. Cannabidiol comes from the plant Cannabis sativa L. and binds to cannabinoid receptors throughout the endocannabinoid system. These receptors are located throughout the body and are prominent in the brain and reproduction tract. Although the effects of CBD on physiology have been researched, little data on the behavioral effects exist, even less so in horses. Calming supplements that may negate aggressive stallion behavior are not suitable due to potential soporific effects that can affect libido. In addition to the effectiveness of CBD to modify behavior in horses, it is also unclear if CBD influences stallion libido. The objective of this study was to evaluate sexual behavior in stallions given a daily CBD supplement for 70 days. Two-year old stallions (n = 8) were assigned to either a Control (CON; n = 3) or Cannabidiol (CBD; n = 4) treatment groups. Cannabidiol was administered at a rate of 0.6 mg/kg BW daily, and equal volume of olive oil was given as a placebo to CON. Horses were weighed every Monday at which time dosages were recalculated to adjust for body weight changes. Behavior data collection occurred twice per week during semen collections. Video data were recorded by placing two cameras, one placed in view of the tease area, and one placed in view of the mount, for behavior data backup. Behavioral data was tallied by handlers calmly calling each behavior as it occurred during collection. The behaviors collected included Flehman’s response, bites, strikes, mounts, high pitch vocalizations, and low pitch vocalizations. Data were analyzed using a Chi Square Test within R Statistical Program (R Core Team). Results were considered significant at P < 0.05. Throughout the duration of the study, all stallions exhibited normal sexual behavior, regardless of treatment. Results showed that total low and high pitch vocalizations, bites, and Flehman’s were affected by treatment (P < 0.01). Cannabidiol-treated stallions had more low pitches (60), compared to CON (58). Cannabidiol-treated stallions had fewer bites (145) compared to the CON (146). Cannibidiol stallions displayed Flehman’s more frequently (270) than CON (236). Flehman’s response and bites were lower for stallions on cannabidiol in Week 1 but increased by Week 10 (P < 0.01), while only Flehman’s response increased in the CON group over time (P < 0.01). These findings indicate that CBD may influence breeding behavior in young stallions specifically when supplemented over time. Further research should focus on the impact of CBD on breeding behaviors in mature stallions and the longevity of the behavioral response to CBD.