In recent years, cannabidiol (CBD) products claiming to reduce anxiety and alleviate chronic pain conditions in both humans and animals have become easily available in many markets. While some are FDA-approved, most are not, and the published research on their efficacy in horses is slim.
Because CBD could be beneficial for behavioral therapy and chronic pain cases, a team from Murray State University, in Kentucky, set out to assess one product’s effects on equine reactivity and movement. Graduate assistant Anna Draeger presented their findings at the Equine Science Society’s 2021 virtual symposium.
What We Know About the Endocannabinoid System
First, Draeger reviewed what scientists know about the endocannabinoid system—a nerve signaling system in the body—and the receptors it involves. She explained that the literature tells us the brain’s hippocampus, deep limbic system, cerebellum, basal ganglia, and prefrontal cortex all have CBD receptors.
“Cohesively, these deal with things like cognition and social behavior, voluntary movement, learning, and emotion as well as endocrine response to environmental stimuli,” said Draeger. “That’s kind of our verification that (CBD) could be a helpful behavioral therapy that we should investigate further.”
A 2020 study on the equine brain confirmed the dorsal root ganglia has CBD receptors, as well. “The dorsal root ganglia houses nerves that relays sensory information to the spinal cord,” she said. “So in terms of chronic pain issues, this could be particularly interesting for the horse’s ability to feel pain.”
Draeger noted it’s also important to consider the parts of the brain where scientists have not confirmed receptors, including the medulla that regulates autonomic features such as breathing and heartbeat.
“This tells us the relative overdose risk of CBD shouldn’t be very high compared to other drugs out there,” she said.
Behavioral and Movement Study Findings
In their study, Draeger and her colleagues recruited 17 Quarter Horse geldings that belong to the university’s equine herd. Eight served as controls, and nine received a daily 100-milligram oral dose of CBD pellets (formulated by EVS Pharm) for six weeks. The team evaluated the horses’ reactivity and movement pre- and six weeks post-treatment.
The reactivity assessment was a novel object test, where an individual exposed each horse to a stimulus (an umbrella opening) to elicit a startle response. Using a heart rate monitor, they measured resting heart rate, stimulus heart rate, and final heart rate one minute later. Live and video evaluators scored each horse’s reaction on a scale of 1 to 5 (1 being no response and 5 trying to flee).
For the movement assessment, handlers led each horse through a series of cones at a walk and trot. The team evaluated their stride length and duration of stance and swing phase using a motion analysis system (Dartfish).
“For the novel object test, we verified a relationship between CBD treatment and reactivity,” said Draeger. “Our treatment horses had consistently lower reactivity levels than the control group.”
Based on the movement evaluation, she said treatment horses took consistently longer than control horses to complete the stance phase of their stride at the walk. At the trot, however, both groups demonstrated reduced stride length and time to completion by the end of the study—findings Draeger called murky.
She said she found the team’s behavior results most encouraging and supportive of further investigations into CBD products. She said the product could be beneficial for horses dealing with transport stress, competition-related stress, or stall rest and owners looking for a supplement that can help reduce their horses’ anxiety without causing significant side effects.
If you’re interested in viewing presentations from the 2021 Equine Science Society Virtual Symposium, you can register for the Symposium until Aug. 2, 2021, and recordings are available for viewing until Sept. 3, 2021.