CBD for Dogs With Aggression: Why and How It Works
CBD for dogs with aggression might be an unexpected remedy for a behavior problem that has plagued countless dogs (and their owners) over the past decades. Statistics show an increase in bite-related hospitalizations, even fatalities.
Being the owner of an aggressive dog is a very stressful experience because of the ever-present, lingering fear that your dog might seriously hurt another person or another dog. This, of course, does not mean that you love your dog any less. You want to help him become a safer member of society and gain a calmer state of mind.
As CBD oil is rising in popularity and taking the world by storm, the pet industry is welcoming a variety of CBD-based products on the market. Many dog owners are now wondering if this is just another hype or something that could actually help their sick, anxious, and aggressive dog. Can CBD truly be helpful for canine aggression?
Aggression in Dogs
How are fear and aggression connected?
Aggression is a strong violent reaction to a perceived external threat. Just like humans, dogs have three natural fear responses: fight, flight, and freeze. Aggression is a manifestation of the fight response. This is how we know that all aggression is essentially born out of fear.
There are many different threats a dog can perceive, such as other dogs, competitors, intruders, etc. Fearful and aggressive dogs cannot discern between an actual threat and a perceived threat. This is why many aggressive dogs are called unpredictable, as their owners struggle to understand their triggers.
Studies have shown that the majority of dog bites happen at home, where one would expect dogs to feel safe. Over half of all people who get bitten are children. Dogs with aggression are suffering from internal fear and opting for the fight response, ultimately making them very challenging to live with.
The idea of a supplement that could help these dogs feel calmer in their environment, not to mention in the world at large, comes as a saving grace to many dog owners who are struggling with fear in their own homes. Thankfully, more and more connections have been made between CBD oil and the improved moods of anxious dogs, giving hope to many owners that their aggressive dogs can be helped after all.
CBD Oil for Dogs
What is CBD? Can a dog get high?
CBD stands for cannabidiol and it comes from the cannabis plant. It can be used as an ingredient in a variety of products, such as edibles, ointments, tinctures, and oils. The CBD in these products is primarily derived from hemp (not marijuana), meaning it contains little to no THC and therefore does not have any psychoactive consequences. Your dog will not get high from CBD.
How does CBD work?
All mammals have a natural endocannabinoid system, known as the ECS. This is a system that regulates many functions in our body, most notable ones being sleep, inflammation, pain, memory, and moods. The way CBD works is by stimulating the ECS receptors, therefore impacting all functions regulated by this system.
Dogs with anxiety and aggression notably suffer from imbalanced moods, sometimes even as a result of physical pain or sickness. Since CBD oil impacts exactly the receptors that regulate moods and pain, it could ease several of these symptoms at once, resulting in a more balanced system and a calmer dog.
CBD Oil and Canine Aggression
Is there proof that CBD can help dogs with fear aggression?
Most of the feedback on successful CBD help for aggressive dogs has come directly from the owners that have reported seeing changes in their dogs’ state of mind. CBD oil can be used as a regular treatment or as extra help on special occasions, such as the New Year’s Eve fireworks, welcoming a new family member, taking a trip to the vet, etc.
Take Barnaby, for example. A 15-year-old dog who has become reactive and fear aggressive as a result of old age. It only took a week of taking CBD for his owners to already notice a change in his mood, which made it easier to work on his behaviors. Stories like these are an inspiration to struggling owners, but they can also be an encouragement to those who work in rescue and daily encounter anxious and aggressive dogs.
One foster dog mom has noticed how much calmer her PTSD fosters are, after giving them CBD treats. She notes that the visible shift in their mood opened the doors to easier socialization and further behavior modification.
While there is much research still to be done on this topic specifically (the first veterinary studies have mainly been focusing on the physical ailments), there are two notable studies that give us a good insight into the value of CBD for aggression in dogs.
In the first study, researchers studied mice who exhibited territorial aggression and found that CBD reduced their aggressive reactions and behaviors. In the cases where aggressive attacks still happened, they were much shorter in duration.
The second study exposed rats to a snake, their predator, with the intent to observe the panic-induced reactions. When faced with the threat, the rats dosed with CBD had significantly diminished fear responses. In both cases, the researchers concluded that CBD could help prevent or reduce fear-born behaviors, such as panic and aggression.
While the research on this topic is still at the beginning, it is evident that the starting point is already more than promising, indicating that there is massive potential for helping fear aggressive dogs with CBD.
Are there any dangers to using CBD for dogs with aggression?
While CBD is generally considered safe, there are still some things you should keep in mind before giving it to your anxious and aggressive dog. Always consult your holistic vet before making any significant changes in your dog’s diet, which includes adding a supplement such as CBD. It is also important to find a good product of high quality, so please do your research before deciding on a final purchase.
The most important thing with CBD is the dosage, which is why you should always carefully read and follow the instructions of the manufacturer. Some possible side effects may include lower blood pressure, drowsiness, and an increased notion of thirst. If you notice any of these symptoms, be sure to check-in with your vet and readjust the dosage.
Finally, it is crucial to understand that CBD can help dogs with anxiety and aggression, but it cannot cure them or take away the cause. It is a very valuable asset for managing aggression in dogs but should not be considered a replacement for consistent training.
Fear is always present in the life of aggressive dogs. It controls their responses, putting their owners in a state of anxiety as well. Many owners are now finding comfort in recognizing the value of CBD oil for dogs with fear and aggression. It can be used alongside their regular training and rehabilitation. CBD oil stimulates the natural system that regulates the dog’s moods, resulting in a calmer dog with a more relaxed state of mind.
While there is still much research to be done, the first studies have been very promising. They indicate that there is an optimistic future ahead for dogs with aggression. This comes as a relief to the owners who are walking this challenging path with them every single day. Since living with an anxious dog often feels like a dead-end street, there is strong hope in knowing the promising effects of CBD for dogs with aggression.
Kriss, Randa. “CBD Oil for Dogs: What You Need to Know.” American Kennel Club, 05/02/2019.
Hartmann, Alice. Lisboa, Sabrina Francesca. Buzolin Sonego, Andreza. Coutinho, Débora. Villela Gomes, Felipe. Silveira Guimarães, Francisco. “Cannabidiol attenuates aggressive behavior induced by social isolation in mice: Involvement of 5-HT1A and CB1 receptors.” Science Direct, 02/05/2019.
De Mello Schier, Alexandre Rafael. Pinho de Oliveira Ribeiro, Natalia. Cardoso de Oliveira e Silva, Adriana. Cecílio Hallak, Jaime Eduardo. S. Crippa, José Alexandre. E. Nardi, Antonio. Waldo Zuardi, Antonio. “Cannabidiol, a Cannabis sativa constituent, as an anxiolytic drug.” Brazilian Journal for Psychiatry, June 2012.
Luna’s passion for learning about canine psychology and behavior began when she adopted a severely reactive puppy from a local shelter. She is now a big advocate for positive reinforcement and compassionate training. As a writer, she strives to spotlight the topics that fly under the radar and be the voice for all who cannot speak for themselves.
Cannabis sativa L. may reduce aggressive behaviour towards humans in shelter dogs
Among the phytocomplex components of Cannabis sativa L., cannabidiol (CBD) has a recognised therapeutic effect on chronic pain. Little is known about the veterinary use of CBD in dogs. Even less is known on the effects of CBD on dog behaviour, especially in shelters. The purpose of this study was to determine if CBD affects stress related behaviour in shelter dogs. The sample consisted of 24 dogs divided into two groups that were created by assigning the dogs alternately: 12 dogs were assigned to the treatment group and 12 to the control group. Extra virgin olive oil, titrated to 5% in CBD was given to treated group; the placebo consisted of olive oil only, dispensed daily for 45 days. Behavioural data were collected using the ‘focal animal’ sampling method with ‘all occurrences’ and ‘1/0’ methods for 3 h: before (T0), after 15 days (T1), after 45 days of treatment (T2) and after 15 days from the end of the treatment (T3). Treated dogs showed reduced aggressive behaviour toward humans following the treatment (Friedman Test: χ 2 = 13.300; df = 3; N = 12; p = .004; adj. sig. p = 0.027), but the difference in the decrease of aggressive behaviour between the two groups was not significant (Mann–Whitney U test, T2–T0: Z = − 1.81; N = 24; p = 0.078). Other behaviours indicative of stress, such as displacing activities and stereotypes, did not decrease. Despite some non-significant results, our findings suggest that it is worth doing more research to further investigate the effect of CBD on dog behaviour; this would be certainly valuable because the potential for improving the welfare of dogs in shelters is priceless.
Cannabis sativa L., also commonly known as hemp, has provided fabric, oils, food and rope for humans for thousands of years 1,2 . It has also been widely used for its medical and psychoactive effects 1,2 . It has more than 489 chemical compounds including terpenes, hydrocarbons, ketones, aldehydes and phytocannabinoids 3 . The two best known cannabinoids are cannabidiol (CBD) and tetrahydrocannabinol (THC). While the second one is responsible for the psychotropic and toxic effect, both in humans and animals (e.g., 4,5,6,7 ), CBD has no psychotropic effects and has a low toxicity 8,9,10 . Due to its high tolerability 8 , it has been increasingly used in clinical trials for humans and animals (e.g., 11,12,13 ).
Despite the discomfort that many veterinarians feel in proposing cannabis-derived remedies to pet owners 14 , CBD is gradually becoming an important tool for the treatment of pain, inflammation, seizures and anxiety (e.g., 14,15,16 ). In 2019, 14 1940 veterinaries were interviewed: of these, 1806 (93,1%) discussed the use of CBD with owners for management of pain, 1341 (69,1%) for anxiety and 1089 (56,1%) for seizures. Although the use of cannabinoid products to treat animals’ behavioural problems in domestic animals has been recently increasing 17,18 , there is scarce literature on clinical trials to evaluate its effectiveness. Deiana et al. 19 tested different compounds of Cannabis sativa, finding that CBD reduced obsessive-compulsory behaviour in rats and mice. In the same year, another study showed that administration of CBD reduced marble-burying behaviour in mice 20 .
Few studies have assessed the effect of CBD on dog health and behaviour. Deabold et al. 13 studied the pharmacokinetics of CBD in dogs and cats. Their results suggest that orally administered CBD in dogs was not detrimental with a time gap of 12 h or more between one administration and another. Similar results were found by McGrafth et al. 16 : dogs tolerate CBD well if fasting and postprandial bile acids remained stable. Gamble and collaborators 15 found that a CBD-based treatment decreased pain and increased activity in dogs with osteoarthritis.
CBD interacts with organisms through the endocannabinoid system (ECS). In vertebrates and invertebrates, the animal’s ECS is a biological system interacting with both endogenous cannabinoids and the exogenous plant molecules derived primarily from hemp 21 . The ECS owes its name to the previous discovery of some elements’ ability, which constitute it, to interact with THC. In mammals, the ECS is very complex and modulates different kind of organism responses 21 . Through the two principal receptors (CB1 and CB2), it takes part in the anti-inflammatory process 22 , in the management of anxiety 23 , in the immune function 12,24 and in lowering pain 25 . This system is also involved in maintaining homeostasis for different organs and in modulating the nervous and immune systems 21 . Even if 26 and 27 demonstrated that CBD has a low affinity for CB receptors, it is an agonist of 5-HT1A receptors 28 . These receptors are part of a class of receptors (5-HT) that usually interact with serotonin 29 and are strictly associated with physical health 30 , mood 30 and stress [reviewed in 31 ].
Stress is a mental, physiological, or emotional state characterized by a factor that is altering the homeostasis of a living organism 32 . For mammals, the response to a stressor, which can be physical or emotional, as for example infections, burns or anger 33 involves the hypothalamic–pituitary–adrenal axis reactivity (e.g., 34 ), resulting in an increase of circulating glucocorticoids that could result in stress-related disorders 35 .
For dogs, entering a kennel represents a stressful event (e.g., 36,37,38,39,40,41,42,43 ) due to several stressors including exposure to a new context or social and spatial restrictions (e.g., 44 ). In many countries like Italy, where sheltered dogs cannot be euthanased except for health reasons or proven dangerousness according to the law, it is our duty to guarantee them an acceptable level of well-being. There is still a debate on behavioural indicators of dogs’ low level of welfare when in kennels 45 ; however, there is no doubt that displacing activities 46,47,48 and stereotyped behaviours 47,48,49 are both indicators of moderate to high level of anxiety, and consequently discomfort, as well as of pathological behaviour in dogs; in addition, persistent aggressive behaviour, out of context, can be considered a pathological behaviour 50 . As defined in 46 , ”Displacing activities are behaviour patterns (mostly body care activities) characterized by their apparent irrelevance to the situation in which they appear. […] Displacement activities tend to occur in situations of psycho-social stress”. Aggressive behaviour is part of all species’ behavioural repertoire; the ultimate causes that led to its evolutionary selection concern function in intra-and inter-specific competition 51 ; in other words, aggressive behaviour has evolved to allow individuals to be competitive for obtaining the resources necessary for their survival 52 .
Some psychoactive medications, including herbal supplements or pheromonal products, have been used to lower the level of anxiety of dogs (e.g., 53,54 ), but no other studies have evaluated the influence of CBD on dog behaviour. The study was a clinical trial and its purpose was to determine if CBD treatment can decrease disturbed and stressed behaviour in shelter dogs, in terms of decrease in displacing activities, stereotyped and aggressive behaviour.
Materials and methods
Animals and housing
The subjects of this study were 24 domestic dogs (20 neutered males, 2 unneutered males, 2 spayed females) with various kind of behavioural problems, randomly drawn from a list of animals matching the inclusion criteria. The behavioural problems were diagnosed by the kennel’s veterinarians working for the Local Health Unit and the Municipality of Rome. The criteria for selection were: age between 1 and 10 years (estimated by standard veterinary methods); physically healthy; presence of behavioural disorders (detected by the veterinarian); permanence in the shelter for at least 9 months (Table 1). The latter item was included in the criteria to avoid biasing the results by measuring behavioural responses due to acute stress; in fact, the literature reports that dogs entering the shelter have different behavioural, physiological and immunological responses due to acute stress 36,45 . The different sex ratio of the selected dogs was due to the shortage of females that met the parameters for the selection and, at the same time, presented behavioural problems. Eighteen of the dogs were mixed-breed and six were clearly purebred-derived dogs (one Bull Terrier, one Bull Mastiff, one Italian Mastiff, three American Pit Bull Terrier).
Table 1 The 24 dogs selected for the study, their weight, principal behavioural disorder, group and dosage.
The selected dogs showed severe behavioural disorders such as compulsively licking the cage walls, chewing on objects until they were destroyed, coprophagy or having attacks of aggression such as to lead to self-injury; none were under therapeutic, pharmacological or behavioural treatment.
Every day the shelter operators monitored the dogs to spot symptoms (vomiting, diarrhoea) of possible health issues; such occurrences were registered and reported to the responsible veterinarian.
The study was carried out in the dog shelter “Muratella”, the municipal dog shelter in Rome. The dogs were housed in single cages of 4 m 2 with an indoor and outdoor area. The cages were cleaned twice a day, before food distribution. All the dogs could go out in a fenced area (10 × 3 m) adjacent to their cages. A few of them were taken out for a walk inside the shelter by the staff and/or volunteers. Given that changing dogs’ daily routines might be an additional source of stress for them 55 , we maintained their lifestyles through the study.
We calculated that the minimum sample size (shelter dogs’ population = 400; prevalence of stress signals in shelter dogs = 90%; power = 0.80; alpha error = 5%; n1/n2 = 1) was 10 individuals in each group, alternately assigned (group A = treated; group B = control); we include two additional individuals for each group to address possible drop outs.
The dogs belonging to the treatment group were given a CBD based oil while the dogs belonging to the control group were given a placebo. Both were administered every day before the usual meal in the morning, for 45 days. CBD based oil consisted of an extraction from aerial parts and inflorescences of the plant Cannabis Sativa in organic extra virgin olive oil to the proportion of 150 g of Cannabis Sativa inflorescences and aerial parts in 1 L of oil. The extraction was done using the “Naviglio” extractor, titrated to 5% in CBD and THC absence. The placebo consisted of extra virgin olive oil only.
The dosage to each dog was calculated as follow: 1 drop of oil/2 kg of weight, i.e. 5 drops of oil were administered to a dog that weighed 10 kg, 10 drops to a dog that weighed 20 kg and so on. The percentage of body fat was calculated for each dog by means of the conditional body score (BCS): in case of obesity, dogs were given an extra 20% of drops (Table 1).
With and without CBD, the oil administration did not require any kind of particular interaction since the oil was mixed with some meat; in any case, due to their behavioural disorders, most of the dogs did not allow any form of interaction with humans. However, the operators were instructed not to alter the usual quantity and quality of daily interactions.
The observations were carried out live by two previously trained observers, blind to which group (treated or control) the dogs belonged to; an inter-observer reliability test was conducted prior to the trial. The behavioural observations were conducted by a single observer each time who sat in front of the cage; observers did not interact with the dogs, so the dogs became rapidly accustomed to the presence of the observers. The time period of observations ranged from September to December 2018. The 24 dogs were observed exclusively in their home-cage for 12 h each, for a total of 288 h. Before starting the administration of CBD based oil and the placebo, each dog was observed for one hour a day for three consecutive days (T0), at three different times of the day (morning, between 8:00 A.M. and 12:00 P.M. hours; lunchtime, between 12:00 P.M. and 3:00 P.M. hours; late afternoon, between 3:00 P.M. and 7:00 P.M. hours). Twenty-four hours after the last day of T0, the treatment began.
The collection of behavioural data was repeated in the same way in the following intervals: from the 15th to the 17th day (T1) and from the 43rd to the 45th day (T2) of the administration of treatment; from the 15th to the 17th day (T3) after the end of the treatment.
The ethogram utilised for data collection during behavioural observations consisted of more than 100 behavioural patterns (described previously in 43 , see Supplementary Information): by means of the focal animal sampling method 56 , the behavioural patterns of each dog were recorded in a check sheet, utilising the “all occurrences” and “1/0” methods (60 s interval) 56 . The “all occurrences” method provides the number of times a dog shows a specific behaviour (for example the number of times it scratches himself), while the 1/0 method gives the number of predetermined intervals (in this case 60 s) in which the dog exhibits a behaviour (e.g., the number of intervals in which the dog barks) 56 .
The behavioural patterns utilised to collect data during the observations were grouped into categories (Table 2), generated on the basis of information drawn from the literature 41,42 and repeatedly used in the past by our working group 43,57,58 . Since the numbers were not normally distributed, to compare the behavioural frequencies recorded in the different times (T0, T1, T2, T3) for the control and treatment groups separately, we utilised the Friedman test, a non-parametric alternative for a repeated-measures ANOVA, and the Bonferroni correction for multiple comparisons. To compare the difference between treated and placebo group, we utilised the Mann–Whitney U test. A p value of < 0.05 was used to determine significance.
Table 2 The behavioural patterns utilised in this study grouped into categories. For the description of the behaviours, see Supplementary Information.
Data analysis was conducted using the IBM SPSS software.
This study was approved by the Animal Welfare and Protection Office of the Municipality of Rome, which is responsible for sheltered dogs according to Italian laws, and by the Sanitary Local Health Unit Rome 3, which is responsible for the health of the sheltered dogs.
Neither anaesthesia nor euthanasia, or any kind of animal suffering, was part of the study. The protocol was carried out in accordance with the relevant Italian guidelines and regulations.
The inter-observer reliability was measured and it corresponded to r = 0.99 on 5 dogs (9 behavioural patterns).
No dogs showed disease symptoms during the study, except for one dog (Gargamello, under treatment) that had a single episode of diarrhoea, during the second day of T2, which disappeared without pharmacological intervention; so we did not exclude this dog from the study. In this study, dogs well tolerated olive oil both with or without the addition of CBD.
The median aggressive levels at T0 looked different for the two groups, but the test for homogeneity applied to the treated and control groups at T0 revealed that this difference was not significant indicating that there was no significant difference in the median level of aggression in the two groups at the start of the study (group A: median = 6.0, IQRs 17–0.75; group B: median = 2.0, IQRs 4.5–0; Mann–Whitney U test, T0: Z = 48; N = 24; p = 0.150).
Aggressive behaviour towards humans decreased significantly over time in CBD treatment group (Friedman test, T0, T1, T2, T3: χ 2 = 13.300; df = 3; N = 12; p = 0.004). However, in the pairwise comparisons, only the T0-T2 comparison was significant (p = 0.004, adj. sig. p = 0.027) (Fig. 1).
Aggressive behaviour towards humans of dogs treated with cannabidiol (CBD) at the start of the study (T0), after 15 (T1) and 45 (T2) days from the beginning of the treatment, and 15 days after the end of the administration of CBD (T3). **p < 0.05; the black bars within the box plots indicate the median; the dots represent the outliers.
On the contrary, in the control group the aggressive behaviour towards humans did not decrease due to the administration of olive oil (without CBD) (Friedman test, T0, T1, T2, T3: χ 2 = 6,268; df = 3; N = 12; p = 0.09; Fig. 2).
Aggressive behaviour towards humans of dogs receiving olive oil as a placebo at the start of the study (T0), after 15 (T1) and 45 (T2) days from the beginning of the treatment, and 15 days after the end of the administration of olive oil (T3). The black bars within the box plots indicate the median; the dots represent the outliers.
The reduction of aggressive behaviour toward humans was marked in the treated group, but the difference between the treatment and control groups in the decrease of aggressive behaviour towards humans was not significant (Mann–Whitney U test, T2-T0: Z = − 1.81; N = 24; p = 0.078; Fig. 3).
Difference in aggressive behaviour towards humans at different times (T0 = before the start of the experiment and T2 = 45 days from the start of the experiment) for dogs treated with cannabidiol (CBD) and dogs in the control group (receiving olive oil as a placebo). The black bars within the box plots indicate the median; the dots represent the outliers.
Concerning the stress related behavioural patterns (stereotyped behaviour and displacing activities), our results did not show any effect of CBD on their frequencies (Friedman test, T0, T1, T2, T3: χ 2 = 2,136; df = 3; N = 12; p = 0.545; Fig. 4; χ 2 = 0,479; df = 3; N = 12; p = 0.923; Fig. 5).
Stereotyped behaviour of dogs treated with cannabidiol (CBD) at the start of the study (T0), after 15 (T1) and 45 (T2) days from the beginning of the treatment, and 15 days after the end of administration of CBD (T3). The black bars within the box plots indicate the median; the dots represent the outliers.
Displacement activities of dogs treated with cannabidiol (CBD) at the start of the study (T0), after 15 (T1) and 45 (T2) days from the beginning of the treatment, and 15 days after the end of administration of CBD (T3). The black bars within the box plots indicate the median; the dots represent the outliers.
Finally, the analysis of all behavioural patterns of the dogs, related to attention and interaction with the environment (looking outside/observer/volunteer, raising of ears and looking outside/at observer/at volunteer carefully, dozing, sniffing object/observer/volunteer) suggested that the treatment with CBD did not reduce the level of attention of dogs and did not make them less perceptive of the environment and of the stimuli that surrounded them (Friedman test, T0, T1, T2, T3. Attention: χ 2 = 6,300; df = 3; N = 12; p = 0.09; dozing: χ 2 = 4,361; df = 3; N = 12; p = 0.225; sniffing: χ 2 = 3,769; df = 3; N = 12; p = 0.287).
According to the information found in the literature (e.g., 13,16 ), our dogs did not show any of the symptoms referable to CBD intolerance. Daily monitoring of the health of the dogs under observation allowed us to evaluate any eventual pathological responses to olive oil, CBD or both. Given the occasional and rare occurrence of intolerance symptoms (one isolated episode of diarrhea), it is possible to conclude that the olive oil treatment, with or without CBD, was well tolerated.
Although the difference in the decrease of aggressive behaviour between the control and the treated group was not significant, possibly due to the small sample size, our results suggest that the treatment with CBD could reduce the frequency of aggressive behaviour towards humans and highlights the need for further studies.
There are in the shelter, of course, temporal and spatial limitations that vary from shelter to shelter, which could affect the results. As it is well known 43,58 , sheltered dogs in general and the dogs in this study in particular, suffer from inter- and intra-specific social deprivation, total lack of interactions at night, and lack of exercise because they are in cages. In trying to minimize the number of variables that could have affected the results in such a variable environment, we chose dogs that had been in shelter for at least nine months and displayed signs of chronic stress. In fact, dogs entering the shelter have behavioural responses due to acute stress 36,45 . According to these considerations, the results presented here acquire value since they suggest a possibility of response to the treatment in a challenging environment, that could be even greater in an environment where the limitations described above are less present and the possibilities to control the dogs are greater. Many attempts have been made to classify aggressive behaviour in domestic dogs; 59 combined the descriptive and functional classification system, describing a typical aggression sequence. The same author claims that if the aggression sequence is altered, this indicates that the aggression has reached a pathological level. Additionally, when the frequency of aggressive behaviour is so high that it occurs out of context, becoming unpredictable, it can be considered pathological 50,60 .
The dogs involved in this study were selected because they showed behavioural symptoms that lead to a diagnosis of behavioural disorders and one of the symptoms was excessive aggressive behaviour. Aggressiveness is a very complex phenomenon: the muscles contract, ready for action, the hair stands up, the pupils dilate, the heart beats at a higher rate, blood pressure increases; the rise of the latter carries to all the cells of the body a frantic but surprisingly well coordinated variety of hormones, cytokines and other molecular messengers that inform the cells of the body about the situation: ‘we are going to attack!’.
In general, it would be an erroneous approach to try to ascribe the hyper aggressiveness of a dog to a few causes; moreover, it would be equally wrong and naive to neglect the possibility that the alteration on several levels of the complex system underlying aggression does not cause a chronic state of malaise for the animal. Many of the dogs in this study showed excessively frequent aggressive behaviours. Some of them showed a high level of aggressiveness before entering the kennel, but their permanence in that environment may have increased it or it may have been brought about in dogs that did not present it to start with.
Takahashi et al. 61 suggested that social stress could induce excessive recurrent aggressiveness that becomes maladaptive because it brings about a dysregulation of the immune system. These authors also suggested that the dysregulated immune responses vary according to the rank of the individual, but it was not possible to evaluate this variable in the dogs under study because, due to their high level of aggressiveness, it was necessary to house them individually. What remains beyond doubt is that their behaviour denounced a high level of malaise.
Our results clearly suggest that CBD treatment might be effectively used to improve welfare in dogs housed in a shelter.
However, if CBD treatment causes a reduction in the aggressive behaviour of the dogs, this effect, in turn, might improve the relationships between the dogs and the staff of the kennel, facilitating dog management and increasing the level of dog welfare; in fact, it has been found that walking on a leash or having physical contact with humans improves the level of dog welfare housed in a shelter 58,62,63 .
Other categories widely used to evaluate dogs’ well-being are displacement activities and stereotypies. They are recognized to be a flag of physical and emotional discomfort in humans and in non-human animals 46,47,48,49 . Our results did not show any effect of CBD on the reduction of those behavioural patterns. In humans, an antipsychotic activity of CBD was assessed and found to reduce the occurrence of apomorphine-induced stereotypies 64 , but the mechanism by which CBD exerts its anxiolytic effects has not been fully clarified, yet. In rodents, an effect of CBD has been found on stereotyped behaviour because it reduced marble burying behaviour following intraperitoneal administration 19,20 , but this effect was not observed reliably when CBD was administered orally 19 . In this study, the lack of effects on dogs’ anxious behaviour attributable to the administration of CBD may be due to oral instead of intraperitoneal administration, as studies on rodents 19,65 and dogs 66 have indicated.
In this study, we also did not find any effect of CBD regarding the reduction of displacement activities. However, before discussing this lack of effect, a premise is due. Some authors suggested that displacement activities are behavioural constituents of the adaptive stress response 67 ; morphologically, in nonhuman primates these behavioural patterns have something to do with body care: self-grooming, scratching, body shaking, stretching and yawning. They can be associated with different kinds of situations but all situations have in common uncertainty and anxiety as the stressful causal factors 46 ; some pharmacological studies, reviewed in 67 , confirmed that displacement activities (mainly scratching) are a valid measure of stress in nonhuman primates and human subjects. In domestic dogs, an indirect suggestion comes from 58 who found that the frequent display of displacement activities such as self-grooming, scratching and body shaking, are associated with a lower level of antioxidant capacity in shelter dogs. There are very few papers on the effect of different treatments in this behavioural category 68 , for example, did not find an effect of the appeasing pheromone in reducing displacement activities in shelter dogs. Despite the evidence that, through the analysis of some physiological parameters, some drugs reduce the stress level in dogs, such as gabapentin 69 or clonidine 70 , the drug effect on stress-related behaviour has been neglected. Furthermore, no experiments to investigate the neurobiological correlates of displacement activities and their relationships with negative emotional states have ever been carried out in the domestic dog. Thus, in this species, it is not even clear which behavioural patterns can be considered displacing activities that, in turn, are behavioural components of the adaptive stress response, probably causing anxiolytic effects. Future studies should be focused on both these aspects of neurobiology in domestic dogs.
One of the most robust results of this study is that CBD treatment did not decrease the activity of the dogs studied, as already highlighted for other species 20 . This is an important point because a decrease in dog activity could have reduced aggressive behaviour and biased the results. Dogs under treatment displayed the same level of attention towards the environment before and after the treatment.
Future studies should include a larger sample of sheltered dogs treated with CBD in order to confirm the action of CBD on some behavioural patterns, which would increase the level of dogs’ welfare.
In this study, we assessed the effects of CBD on dogs’ behaviour. An administration of CBD every 24 h did not result in any effects on behavioural categories related to stress but seemed to reduce aggressive behaviour. Additional investigations are necessary to widen the sample of dogs and to combine a behavioural therapy with CBD administration. Our results pave the way for further behavioural and veterinary studies to understand if CBD could be efficacious also in the treatment of behavioural disorders.