Abstract: The aim of this study was to determine factors that might be linked to dominance aggression in pet dogs. Our results show that possession aggression is the first manifestation of dominance aggression and its basic form. Modifiable and non-modifiable factors that are associated with higher levels of dominance aggression and depend on the owner include first time ownership, a lack of obedience training, the owner not being the main obedience trainer, spoiling the dog, not using physical punishment, acquisition as a present, as a pet, impulsively, or to guard and spaying female dogs. Modifiable factors have the greatest influence on dominance aggression in dogs. Dog-dependent factors (gender, breed, age, size and coat color) are fewer than owner dependent factors. There was an association between certain dog behaviour patterns and higher level of dominance aggression.

INTRODUCTION

Dominance aggression is the most common form of aggression (Beaver, 1983; Polsky, 1996) and up to 59.2% of aggressive dogs have been reported to have dominance aggression (Beaver, 1983). Dominance or competition aggression is a form of aggression towards family members (people and other dogs) in which the dog fights for a higher hierarchical position within the family (Landsberg et al., 1998).

The dog usually singles out certain family members, it wants to dominate (Landsberg et al., 1998; Polsky, 1996) and may target one or more family members. It is suggested, that a more compliant family member might be victimised more often than someone who is firm with the dog but some dominantly aggressive dogs challenge the more forceful family members instead (Overall, 1999). Others believe a dominant dogs typically shows no aggression towards a person who is clearly dominant or submissive because the dog would prefer to challenge people with no definite hierarchical position (Uchida et al., 1997).

In dominance aggression, the dog tends to attack family members in order to protect possessions it considers vital, or as a form of resistance to dominance signals emitted by another member of the family (Wright 1991). This definition includes the concepts of both possession and dominance aggression. In fact, many authors include situations of possession aggression when evaluating dominance aggression (Beaver, 1983; Crowell-Davis, 1991; Dodman et al., 1996; Uchida et al., 1997; Wright, 1991), they consider possession aggression to be an expression of dominance aggression.

The behavior of the owner towards the dog can favour dominance aggression. Approximately 40% of dominance aggression situations are linked to non-authoritarian dog owners, who have carried out only minimal basic obedience training with the dog or even none at all (Grognet and Parker, 1992). Dogs that show dominant aggressive behaviour towards their owners have been usually spoiled, treated like human beings (O'Farrell, 1997). Such dogs, for example, may have been allowed to get on the bed or armchair, sleep on the family’s bed and given extra food from the family’s meals.

Having in mind that dominance aggression is the most common form of dog aggression and is such an important problem (Beaver, 1983; Polsky, 1996), the aim of this study was to determine which factors might be linked to dominance aggression and thus aid in understanding and controlling this phenomenon in pet dogs.

MATERIALS AND METHODS

Study sample: A total of 711 dogs (354 males and 357 females, 594 purebred and 117 mixed breeds) older than 12 months were assessed by an interview with their owners.

The study was carried out in 5 cities in Spain (Almeria, Cordoba, Granada, Jaen and Madrid) with a total population of about 5 million people. The interviewer was always the same person (male, veterinary, 28 years old) and the dogs lived with their owners. Interviews were carried out with dog owners who were taking their pets for a walk. Subjects were opportunistically selected (owners who were taking their dogs for a walk) 62% of the owners approached agreed to participate in the study. The interviewer was well trained to classify each dog through its morphological characteristics in each corresponding breed. So, the interviewer verified the owner’s information about the breed of the dog.

Every breed studied had a minimum of 4 dogs. The 594 dogs that were assessed belonged to 47 pure breeds, grouped according to the world canine association (FCI = Fédération Cynologique Internationale) categories.

The mixed and pure breed dogs were classified into three categories: small (>10 kg), medium (10-20 kg) and large (>20 kg). Intact dogs constituted 92.54% of the population. The English cocker spaniels were subdivided into 3 different groups (blonde, black and particolour) since several studies have observed a relationship between the colour of an English cocker Spaniel’s coat and its level of aggression.

This study was reviewed and approved by the department of veterinary medicine and surgery (University of Cordoba).

Description of the survey: The survey gathered information on 72 variables many of which were significantly linked to dominance aggression. However, this study will only discuss the most significant associations, certain variables that have been reported as significant by other authors and those that were considered by this study to be of particular interest.

We assessed the dog’s level of dominance aggression through 9 situations from a list of situations that are used to estimate a dominance score in the dog (Uchida et al., 1997; Guy et al., 2001a). Owners are rarely able to report the motivation of their dogs behaviour with any accuracy, therefore, we showed the owners 2 photos: A typical dog with dominance aggression postures (erect, stiff posture, the tail held high and the ears erect and tilted forward) and a typical dog with a fearful motivated posture (lowering its head, flattening its ears against its head, tucking its tail between its legs and avoiding eye contact). We considered a situation to be a positive instance of dominance aggressive behaviour when the dog was growling, snapping, biting or baring its teeth towards family members and the owner was sure that the situation happened with the typical dog dominance aggression postures showed in the photo. The dog was awarded a score of between 0-9 points according to the number of these situations that elicited the behaviour. These situations were:

We assessed the dog’s tendency to bite during the previous situations (if the dog bit, one point was awarded). Hence, the score for the dog’s tendency to bite was rated between 0 and 9 points. We consider 4 groups for the dog’s tendency to bite: High (>4), medium (3-4), low (1-2) and null (0).

We also assessed how spoiled the dog was, based on 5 situations (giving it extra food from the family’s meals when they were eating; allowing it to lie on the sofa/armchair/chair; allowing it to get on the bed; allowing it to sleep in the bedroom; allowing it to sleep on the bed with the owner). If the answer was affirmative, 1 point was awarded; hence, the score for spoiling ranged between 0 and 5 points.

We consider a dog to have received basic obedience training when the owner reported that it responded to at least 3 orders, such as: come, sit (lie) down, leave (an object it has in its mouth), stay, wait and so on.

Statistical analysis: The dogs obtained a score of between 0 and 9 points for dominance aggression. In order to study discontinuous variables, 3 groups of dominance aggression were created: low (0-2 points), medium (3-6 points) and high (7-9 points). Variables were analyzed independently, nevertheless four variables (dog sex, dog age, dog breed and neutered status) were locked during statistical analysis of each variable due to their potential to act as confounders because they are highly significant variables and other variables studied may depend on them. SAS (2000) was applied in order to carry out the following statistical analyses:

RESULTS

Interview completion: The average time taken to complete an interview was 28 min.

Factors analysed: There were no factors with a significance level between 0.05 and 0.001.

Highly significant factors (p<0.001): Highly significant factors and its components with higher levels of dominance aggression are shown in Table 1. The dominance aggression mean score of 10 factors are dependent on other factors (Table 1): Breed, dog’s size, owner’s sex, owner’s age, other pets in the family (any pets), first time ownership, owner’s level of education, type of food, how often the dog is fed, the total time the owner spends with the dog.

Insignificant factors (p>0.05): Factors that were not significant were: Children in the family, the main person who fed, walked or played with the dog, playing competitive games with the dog, the dog’s favourite games, the age of the dog when it was adopted by the owner and the place from which, it was acquired, whether the dog had passed from one owner to another, whether it had suffered an illness during the first 16 weeks of life and whether the dog barked a lot, or the owner described the dog as stubborn or nervous.

Table 1:	Highly significant factors (p<0.001)
*Factors with the upper index number depend on these factors: Obedience training1, 2, 3, 5, 6, 7, 8, 9, how spoiled the dog is1, 2 3, 5, 6, 7, 8, 9, the type of punishment used with the dog1, 2, 3, 5, 6, 7, 8, 9, the time the owner spends walking the dog1, 2, 5, 7, 9 and the total time the owner spends with the dog1, 2, 7, dog’s size1, 8, 9, the time the owner spends walking the dog10; CV = Continues Variable; DV = Discontinues Variable

DISCUSSION

They consider possession aggression to be an expression of dominance aggression (Beaver, 1983; Crowell-Davis, 1991; Dodman et al., 1996; Uchida et al., 1997; Wright, 1991; Pérez-Guisado et al., 2008c) or different types of aggression that are independent, but they can be linked (Overall, 1999; Borchelt and Voith, 1982). Levels of dominance aggression were assessed through 9 situations; the first 3 correspond to possession aggression and the other 6 correspond to pure dominance aggression. The results revealed that 100% of dogs that displayed pure dominance aggression in at least one of the situations also scored positively in the 3 situations of possession aggression (giving a final score of 4 points or more). It is also interesting to observe that in the global evaluation of dominance aggression, 100% of dogs that scored positively in 3 or less situations of dominance aggression (gaining a final score of 3 points or less) only display this behaviour in situations of possession aggression. These results might shown that possession aggression is really dominance aggression and is the first and most basic manifestation of dominance aggression. Certain authors argue that they are separate forms of aggression since a dog can display possession aggression without dominance aggression (Overall, 1999). However, this study demonstrates, the link between the two forms of aggression, showing that the most basic characteristics of dominance aggression are found in situations related to possession aggression. Possession aggression does not necessarily evolve into typical dominance aggression. However, it is always the starting point leading towards greater manifestations of dominance aggression since, in these situations, possession aggression is always involved. In fact, certain studies claim that many dog owners whose pet displays dominance aggression remember that their dogs had possessive problems (associated with food) when they were puppies (Crowell-Davis, 1991).

The results of this study (Table 2), support the view expressed by many authors that dominance aggression problems are much more common in male then female dogs (Borchelt, 1983; Cameron, 1997; Crowell-Davis, 1991; Overall and Love, 2001; Pérez-Guisado et al., 2006, 2008a, c). This is probably due to the effect of androgenic hormones that favour dominant or competitive behaviour in males.

Table 2:	Dominance aggression’s mean scores

Crowell-Davis (1991) states that dominance aggression is more common in purebreds but our results show that there are no significant differences between pure and mixed breeds. Logically, the genes of mixed-breed dogs include a combination of the parents genetic features. Hence, some mixed-breed dogs will have a higher tendency to develop dominance aggression owing to the parents genetic attributes. In a large sample of mixed- breed dogs, including many different sizes and crossbreeds, the logical outcome would be for the dominance aggression average to be statistically equal to the average of purebreds. This is supported by our results (Table 2).

Our results confirm that English Cocker Spaniels with a single colour coat are more aggressive than particolour dogs (Podberscek and Serpell, 1997a, b; Pérez-Guisado et al., 2006) and more aggressive behaviour is displayed, in decreasing order, by blonde, black and finally particolour coated dogs (Podberscek and Serpell, 1996; Pérez-Guisado et al., 2006, 2008 a, c). The scores are 3.17, 2.14 and 1.41, respectively.

Guy et al. (2001a, b) state that small dogs tend to have more aggression problems towards people than bigger dogs. The results of this study support this statement, since it found an inversely proportional relationship between dog size and dominance aggression. Dogs in the small dogs group display the highest levels of dominance aggression followed by medium-sized and finally large dogs group (Table 2). This inversely proportional relationship is probably due to the positive relationship found between dog size and the following factors: not spoiling the dog; the use of obedience training; the use of physical punishment and the time spent generally with the dog and taking it for walks. Small dogs are the most spoiled, the least trained and the least physically punished. They are also taken for the fewest/shortest walks and have the least time dedicated to them.

Age plays an important role in canine aggression problems, since these problems usually begin before the dog is one year old (Guy et al., 2001a). Nevertheless, it usually increases between the first and third year (Borchelt and Voith, 1982). Even though dominance aggression begins at an early age, this problem does not usually start to worry the owner until the dog is between 6 and 24 months old (Cameron, 1997). Dominance aggression problems are first diagnosed in males between 12 and 36 months and in females between 2 and 36 months (Overall and Love, 2001). Our results complete this picture: dominance aggression increases progressively, reaching its maximum level between the ages of 5 and 7. After the age of 7, it begins to decrease with age (Table 2).

Our results (Table 2) confirm that obedience training is very important in controlling the incidence of dominance aggression (Jagoe and Serpell, 1996; Pérez-Guisado et al., 2008 b). This study also confirms that there is a positive relationship between dog size and obedience training: larger dogs are more likely to receive training than small dogs (Kobelt et al., 2003). These findings contradict those of Voith et al. (1992), who state that there is no correlation between obedience training and dominance aggression. It can also be suggested, that the person who trains the dog is also an important factor (Table 2): When the owner is in charge of obedience training, the dog displays lower levels of dominance aggression than if it is trained by someone else. This could be because the dog identifies the person who carries out obedience training as the dominant member of the family and it accepts a subordinate position in the relationship.

Having an anthropomorphic attitude towards the dog, spoiling it and treating it like a person, can cause behavioural problems such as dominance aggression (O'Farrell, 1997; Pérez-Guisado et al., 2008 b). For example, Guy et al. (2001b) found an association between whether the dog slept on someone’s bed in the first 2 months of ownership and dominance aggression. Jagoe and Serpell (1996) discovered a link between the dog sleeping near the owner and an increased incidence of competition aggression. Our results support these authors statements (Table 2) but differ from the findings of Voith et al. (1992), who state that there is no link between spoiling the dog and dominance aggression.

Dogs that are disciplined only verbally have more behavioural problems such as separation anxiety (Takeuchi et al., 2001). Moreover, a lack of authority is associated with dominance aggression (Grognet and Parker, 1992; Pérez-Guisado et al., 2008b). Our results show that dogs that are punished only verbally have the highest dominance aggression average. Dogs that are physically punished, however, have the lowest dominance aggression average (Table 2). This means that physical punishment could be the most effective way of avoiding dominance aggression. Solarz (1970) states that physical punishment is the best way of restoring the owner’s dominance over the dog. They however, would not advise the use of physical punishment with dominantly aggressive dogs (Crowell-Davis, 1991; Overall, 1999). Our results show that it is even less effective to punish the dog only verbally than not to punish the dog at all (Table 2). This might be due to the fact that many dog owners are not as hard as they should be when they punish their dogs verbally, that physical punishment is less ambiguous than verbal reprimand or maybe using only verbal reprimand is linked with anthropomorphic attitudes towards the dog. The dog realises that its bad behaviour does not lead to negative consequences, but that it does serve to attract its owner’s attention. Thus, the owner is actually reinforcing the dog’s bad behaviour. Dogs and wolves resolve their conflicts using force when warning signals are not enough and this is how the dominant dog/wolf is established in the pack. For that reason and bearing in mind the results of our study, it is clearly a mistake to treat a dog as a person and not to use physical punishment when necessary, as a way of establishing dominance over a dog. Nevertheless, it must be noted that although, this method could be a way of establishing or restoring dominance over puppies or small dogs, it could be dangerous if attempted with physically powerful dogs.

Podberscek and Serpell (1997a) found a relationship between low levels of dominance aggression and owners over the age of 65, owners that spend more time with their dog and owners that spend more time walking their dog. Our results confirm these statements (Table 2) and that dogs that belong to owners under the age of 30 have the highest dominance aggression average. We also found an inverse relationship between the amount of time, the owner spends with the dog in general including taking it for walks and dominance aggression (Table 2). We believe that all this is due to the fact that old people is more responsible and have more leisure time than young people and when the owner spends leisure time with the dog, he is reinforcing their relationship. If the dog understands that all enjoyable activities in this relationship depend on the permission of the owner, it will accept a subordinate position.

CONCLUSION

ACKNOWLEDGEMENT

This resaerch was supported by research grant from the Ministry of Education and Science of Spain. We are grateful to all the owners dog who responded to the survey unselfishly.