Statement of the Problem

A dog was examined because of aggression toward family members, particularly the 15-year-old daughter in the family.

Signalment

The dog was a 13-month-old castrated male Cocker Spaniel.

History

The household consisted of a husband and wife, their 15-year-old daughter, and 2 older children. The dog had been obtained at 8 weeks of age from a breeder who had described the dog as timid. At 16 weeks of age, the dog began growling at the daughter when she picked him up or put her face next to his. Over time, the dog began to stare, snarl, and lunge at the daughter if she got too close to the dog on the floor, if she tried to take a high-value toy from the dog, or if she tried to move the dog off the bed or couch. The dog would stand stiffly at the top of an enclosed stairway, then stare and growl if the daughter tried to come up the stairs. The dog had bitten the daughter once as she tried to roll the dog on its side for petting. The bite caused 2 superficial punctures on the daughter's arm that did not require medical treatment. The daughter would respond to the dog's aggressive behaviors by backing away, scolding the dog, or sending the dog to its kennel. The dog also growled occasionally at other family members in the same contexts; however, these incidents were much less frequent and had never progressed past growling. The wife reported that compared with other family members, the daughter used a louder voice, changed behaviors more suddenly, and played more roughly with the dog.

Physical Examination Findings and Laboratory Results

Results of a complete physical examination of the dog were normal. To help rule out medical causes for the dog's aggressive behavior and to assess hepatic and renal function prior to treatment with psychotropic medications, a CBC and serum biochemical profile, including measurement of serum thyroxine concentration, were performed. All results were unremarkable.

During a behavioral examination, the dog growled when the examiner entered the room, but then approached with a nonreactive, friendly demeanor. The dog reacted to noises and sudden movements by tucking its tail, lowering its body, and flattening its ears back; the wife reported that these postures were common. The dog accepted food treats that were tossed to him and subsequently accepted them from the examiner's hand. With direction, both the wife and daughter were able to elicit compliance with “come,” “sit,” and “down” commands, although the dog approached the daughter more timidly and immediately returned to sit by the wife when food was not evident. The dog exhibited no assertive postures during the appointment.

Diagnosis

The differential diagnoses for human-directed aggression that were considered included ownerdirected aggression, fear-related aggression, pain-related aggression, and play aggression. Congenital, infectious, metabolic, and hormonal diseases that could contribute to aggression were also considered but were ruled out on the basis of the normal physical examination and laboratory testing results. Neurologic diseases were also considered unlikely because the dog appeared to function normally except in specific contexts with reproducible triggers. Had the serum thyroxine concentration been low, complete testing to more fully evaluate thyroid function would have been recommended. However, serum thyroxine concentration was within reference limits (1.8 μg/dL; reference range, 1.0 to 4.0 μg/dL).

Owner-directed aggression occurs more commonly in Cocker Spaniels than in the general population of dogs, reflecting a probable genetic basis.^1,2 Dogs with owner-directed aggression may respond aggressively towards members of their social group in situations that involve conflict over control of resources, such as preferred resting areas, the dog's body space, and possessions (eg, toys, food items, and favorite people).³ These dogs typically become more aggressive when they are scolded or punished; however, this can also be true for dogs with fear-related aggression, in which fear increases in punishment contexts.⁴ Owner-directed aggression was previously known as dominance aggression, a term now reserved for resource-aggressive dogs that exhibit dominant body postures and an assertive temperament.^3,5 The dog described in the present report was not assertive or confident, and a diagnosis of owner-directed aggression was made on the basis of the dog's dominant posturing in certain contexts (ie, standing above the daughter on the stairs while staring and blocking her access) and aggression in contexts typically viewed as involving competition over possessions or social control.

Dogs with fear-related aggression may respond aggressively when they feel threatened by some aspect of an interaction with a human, such as when a person assumes assertive body postures or facial expressions.^4,5

A diagnosis of fear-related aggression was made for the dog described in the present report because of the history of the daughter's more direct and erratic mannerisms and the observation during the behavioral examination of fearful body postures and hesitancy when approaching the daughter. The historical presence of both fearful and dominance posturing may have reflected the co-occurrence of multiple aggressive disorders in the dog.

Pain-related aggression was ruled out by the absence of pain responses or abnormalities during physical examination. Play aggression was considered because of the dog's age and the history of the daughter playing roughly with the dog, but was ruled out by the absence of playful posturing during aggressive episodes.

Treatment

The owners were advised that the dog posed a safety risk, especially to the daughter, and that interacting with the dog more safely would require certain “rules.” The dog was fitted with a head collar^a and basket muzzle. Treatment focused on avoiding situations that had elicited aggression in the past, asking for and rewarding deferential behaviors to give the owners greater control, desensitization and counterconditioning to improve the dog's responses to the daughter, and antianxiety medication. The owners were given verbal and written instructions and coached as they practiced behavior modification techniques.

Family members were asked not to scold or punish the dog, bend over the dog closely, put their faces next to the dog's, allow the dog on the furniture, or give the dog high-value toys or food that the dog was likely to guard. Instead of approaching the dog, the owners were advised to have the dog come to them. In addition, the daughter was advised to talk to the dog with a soft, happy voice, and to avoid staring at the dog and playing rough games. The owners were instructed to initially leave the head halter and a drag line on the dog when in the house so that they could control the dog without confrontation if necessary. The owners were shown how to teach the dog to wear the muzzle happily so that it could be used to reduce the risk of bites as necessary.

The directions to the owners served several functions. Making interactions with the daughter less threatening served to reduce her intensity as a fear-inducing stimulus, which was important for the process of desensitization. Avoiding problem situations also increased the safety for all family members and prevented inadvertent reinforcement of aggressive responses.

The owners were also instructed to no longer respond to the dog's solicitations, but to have the dog earn all attention by doing something for the owners. The owners were instructed to carry food tidbits and to intermittently ask for and reward behaviors such as come, sit, down, and stay. As the dog became eager to comply, the owners were to reward the dog's acceptance of reduced-intensity trigger situations, such as bending slightly over the dog, and to very gradually increase the intensity of the triggers after successful acceptance of less intense triggers. The daughter was instructed to not participate in any unpleasant tasks with the dog, such as ear cleaning, but was to be responsible for 75% to 80% of the earning opportunities each day.

Treatment with fluoxetine (1 mg/kg [0.45 mg/lb], PO, q 24 h), a selective serotonin reuptake inhibitor, was prescribed. Fluoxetine is used to modulate mood and decrease anxiety in human patients⁶ and has been shown to result in decreased signs of dominance-related aggression in dogs.⁷ The owners were advised that fluoxetine was not approved for use in dogs and that its use did not decrease the importance of behavior modification or eliminate the risk of biting.

Follow-up

After 1 month, the owners reported that the dog seemed “happier.” The daughter interacted with the dog most days without eliciting aggression, and the dog was tolerating fluoxetine administration without any apparent adverse effects. The dog would still occasionally block the daughter's access to the upstairs and growl during play or if she put drops in the dog's ears. In the examination room during a follow-up examination, the dog exhibited almost no fearful body postures. The dog was responsive and remained eagerly focused on either the wife's or the daughter's target hand during the entire examination. The owners were reminded that the daughter should not put drops in the dog's ears. If the dog growled during a game, the owners were to end the game and withdraw all attention. In addition, the daughter was instructed to call the dog to her before approaching the stairs.

Three months after the initial examination, the family reported only rare growls that occurred almost exclusively in high-intensity trigger situations as, for example, if they bent tightly over the dog or restrained the dog in a hug. A further follow-up examination was recommended for 5 months after the initial examination.

Ten months after the initial examination, the dog was returned because of gradual recurrence of aggression toward the daughter. Questioning revealed that the behavior modification plan was being used inconsistently and that the older sister would comfort the dog when it was aggressive. The treatment plan was reviewed. Results of follow-up laboratory testing were normal.

One month after this recheck examination, the dog was again doing well. However, 2 months after the recheck examination, the wife reported that the dog suddenly lunged at the daughter aggressively and chased her into a bathroom. The daughter was not injured, but the family was frightened and considered having the dog euthanized. Discussion revealed that at the time of the incident, the daughter had been wearing a dark sweatshirt with the hood over her head and had run into the room and quickly bent over the dog to hug it. It was discussed with the owners that a fast approach, bending over, and hugging were predictable triggers, and the heightened response likely occurred because the dog felt threatened by the daughter's hooded appearance. The owners were reminded that the risks of biting would continue and that full compliance with the treatment plan was essential. Euthanasia was discussed as an option but declined by the owners.

Additional follow-up was obtained through twice weekly telephone conversations. The owners regained confidence in their ability to control the dog, and 2 months after the incident, the wife reported that the dog was more relaxed and responsive to the daughter than it had ever been previously. There had been no further incidents of aggression. A plan to try to wean the dog from the fluoxetine if the dog continued to do well for an additional month was discussed.