The popularity of cannabidiol, better known as CBD, has exploded in recent years. Proponents say it provides relief from a nearly endless list of conditions without major side-effects. The second most prevalent chemical compound found in the cannabis sativa plant, CBD won’t get you high, unlike its psychoactive cousin, THC (tetrahydrocannabinol).
So, what’s good for the human must be good for the horse, right? Nobody’s quite sure yet. But scientists are working on determining whether CBD makes a safe effective equine supplement and at what doses.
Kentucky’s Murray State University graduate student Anna Draeger presented “Cannabidiol in the horse: Effects on movement and reactivity” at the recent 2021 Equine Science Society (ESS) virtual symposium. She noted only a few of the many CBD products for both animals and humans are federally approved.
Nevertheless, she said, they’re worth evaluating for use in behavioural therapy and chronic pain based on what’s understood about the mammalian endocannabinoid system. This biological system consists of endocannabinoids (made by the body versus plant-derived CBDs, called phytocannabinoids) and receptors throughout the body, including several in the brain that deal with “cognitive and social behavior, voluntary events, learning and emotion, as well as our endocrine response to environmental stimuli.”
Draeger cited a 2020 study that verified CBD receptors exist in the dorsal root ganglia – nerves that relay sensory information to the spinal cord, which could provide an important link in chronic pain issues. She said it’s also important to note where receptors haven’t yet been found – including the medulla, the part of the brain regulating autonomic activities such as breathing and heartbeat.
“That tells us the relative overdose risk of CBD shouldn’t be very high in comparison to some other drugs out there.”
CBD: Lower Reactivity
For the study, 17 Quarter Horse geldings from the school’s herd were divided into both a control and treatment group. The latter received a 100-milligram oral dose of CBD pellets once a day over a six-week period. Researchers evaluated reactivity and movement pre- and six-weeks post-treatment.
They assessed reactivity with a “novel object test.” Each horse was exposed to a suddenly opening umbrella as he was led around a barn corner to elicit a startle response. Horses wore a heart-rate monitor, and their reaction was also scored on a scale of one (no response) to five (flee attempt) in person and on video.
“We actually didn’t see an effect on heart rate based on treatment or time, which was pretty consistent with research already out there,” said Draeger.
For the novel object behaviour scores, horses treated with CBD were “pretty consistently lower” in reactivity levels than the control group. While “definitely encouraging” for use in stress reduction, she said more research needs to be done to ensure there won’t be negative effects.
Using a video sports analysis system, they also evaluated movement by measuring aspects of stride completion as the horses were walked and jogged through series of cones. Results were relatively inconclusive.
Draeger concluded future studies should consider targeting a specific lameness and increasing CBD dosage.
More Substantial Dose
When Toronto-based equine cannabis research and development company CannaHorse sought to establish an appropriate dose for its trial “Safety and behavioural effects of cannabidiol applied as an oral administration in horses” it consulted the Murray State study.
CannaHorse’s Emma Hill noted to the ESS symposium that they combined Draeger’s suggestion that “a more substantial dose would give better behavioral results” with data from a cannabis formulation used to treat anxiety in humans to arrive at an equivalent equine dose of 250-milligram oral dose of active CBD. This provided maximum bioavailability (amount of a substance that’s absorbed by the body), stability and dosing precision to the eight healthy adult Czech Warmblood horses in the study.
A veterinarian performed a detailed physical exam at seven and one day(s) prior to administration. Clinical observations (i.e. general condition, behavior, appetite, water consumption, colour of urine, colour and consistency of feces, etc.) began seven days before administration and continued until 10 days after. Blood was sampled for CBD concentration at time of administration, two minutes later, then at 10, 20 and 30 minutes and then regularly for 48 hours after.
Behaviour was measured twice prior to administration and then at two, four, six hours until 95 hours after administration. A score system with one denoting a low degree of activity (high relaxation) and five denoting high activity or restlessness was used. Heart monitors measured rate variability as a measure of stress.
In the end, researchers recorded minimal effects on behaviour and no adverse effects – even when CBD was at peak concentration in the blood plasma. “Although,” said Hill, “there is more research needed to confirm safety of a more long-term CBD use in horses, of course. The research is leading to other trials that further investigate safety but specifically for anxiety, gut health and joint pain treatment this aims to enlighten the benefits of CBD and how specifically it can be used in horses.”