It is known that because of brain ageing process and old-age diseases dogs may exhibit an aggressive behaviour and the fear based aggression is more common in old dogs than the other types of aggression (2). None of these statements however, has been confirmed by scientific investigations.
To investigate circumstances of aggressive behaviour we elaborated a questionnaire composed of three parts: environmental, behavioural and an anamnesis. The owners of aggressive dogs were asked to answer the 100 questions. Subsequently each of 71 dogs was examined and submitted to a 2-hour observation with or without stimuli triggering aggression. The dogs were divided into three categories: young (1-3y.), adult (over 3y.) and aged (over 6y. in the case of large size breeds, over 7y. in the case of medium size breeds and over 9y. in the case of small size breeds). The presented aggressive behaviour was classified according to the criteria elaborated by Dehasse (1). We took into consideration whether aggressive behaviour had its onset when a dog reached an advanced age or whether it only intensified then.
The analysis revealed that the older the dogs were, the more fear based aggression cases there were. Among aged dogs it was 56.2%, while among young and adult dogs it was 27.4% and 35.7%, respectively. The prevalence of aggressive behaviour in aged, previously non-aggressive dogs was correlated with the onset of old-age diseases and brain ageing process (62.5%) whereas the intensification of aggressive behaviour had mainly behavioural causes (91.6%). We have observed that in old, previously non-aggressive dogs the critical, distancing and irritable aggression were the most frequently presented types of aggression with the highest rate for the distancing aggression (55.5%). We have also found that severe Cognitive Dysfunction Syndrome may cause an occurrence of critical aggression in old patients. In the three cases of critical aggression, two dogs suffered from severe CDS.
These findings confirm that the fear based types of aggression are more common in old dogs. Interdisciplinary scientific investigations joining veterinary behavioural medicine and gerontology are still infrequent, so these findings contribute to broadening of the knowledge about ageing process in dogs. The number of cases however, is not representative for the general population, thus another investigation is needed. Nevertheless, these findings may help to deal with geriatric dogs' behavioural problems in veterinary practice.