Environmental effects on compulsive tail chasing in dogs

Abstract

Obsessive Compulsive Disorder (OCD) is a neuropsychiatric disorder observed both in humans and animals. Examples of Canine Compulsive Disorder (CD) include excessive tail chasing (TC), light/shadow chasing and flank sucking. We performed a questionnaire survey to investigate the characteristics of compulsive (TC) and its possible associations with environmental correlates and personality in a pet population of 368 dogs from four dog breeds. We observed an early onset of TC at 3-6 months of age and a large variation in TC frequency in all breeds, with an overrepresentation of milder cases. Almost half of the TC dogs showed lowered responsiveness during bouts and displayed also other types of compulsions more often than the controls. Interestingly, dogs that received dietary supplements, especially vitamins and minerals, expressed less TC compared to dogs that did not receive any supplements. Neutered females had less TC, suggesting an influence of ovarian hormones on TC. Tail chasers were shyer and had separated earlier from their mothers than the controls. Finally, our genetic study did not find an association between TC and CDH2, a locus previously associated with the canine flank sucking compulsion. In conclusion, the early-onset and the variable nature of the repetitive behaviour, which is affected by environmental factors such as micronutrients, neutering and maternal care, share several similar components between canine and human compulsions and supports canine TC as a model for human OCD.

Figure 1. The age of onset of tail chasing (TC) behaviour in each breed.

BT =  Bull Terrier, standard, MBT  =  Bull Terrier, miniature, GS =  German Shepherd, SBT  =  Staffordshire Bull Terrier.

Figure 2. Distribution of the dogs according to severity of tail chasing behavior.

Only individuals that exhibit tail chasing behavior are included. Severity is described by the TC_index, which is a sum of two questions “Does your dog chase its tail?”(scale 0–6) and “On average, how much time on a normal day does the dog spent in chasing its tail? “(scale 0–6). (BT =  Bull Terrier, standard, MBT  =  Bull Terrier, miniature, GS =  German Shepherd, SBT  = Staffordshire Bull Terrier).

Figure 3. Summary of the owners’ perceptions on their dog’s tail chasing (TC) behaviour.

Summary of the answers to the following questions a) does TC interfere with dog’s daily activities?, b) has the owners tried to stop the behaviour, c) does the dog stop tail chasing when it is told to and d) while chasing its tail, does the dog react to its name, or other commands? Graphs represent a pooled data analysis including all breeds.

Figure 4. Summary of the owners’ descriptions of the tail chasing (TC) situations.

(a) what precedes tail chasing? (b) how does your dog look after tail chasing? Graphs represent a pooled data analysis including all breeds.

Figure 5. The presence of other compulsions such as fly catching/light chasing behaviour, licking, repetitive pacing and freezing (trance-like behaviour) in case and control dogs.

Case dogs have TC_index≥2, whereas control dogs have never chased tail tails (TC_index = 0). As a measure of the compulsive behaviours (represented in the Y axis) we use index calculated as the sum of numerical answers to questions “Does your dog freeze/chase lights etc.?” from ‘never’ to ‘multiple times per day’ and “On average, how much time on a normal day does the dog spent in that specific behaviour?” from 0 min up to 5 hours or more (Attachment S1). All breeds are pooled for the analysis. Sample size for each group is marked on the top of each bar. Statistical significance is marked following *<0.05, **<0.01, ***<0.001.

Figure 6. Number of case and control dogs who received dietary supplements.

Case dogs have TC_index≥2 whereas control dogs have never chased tail tails (TC_index = 0 ). Dietary supplements are divided into the following categories: vitamins, minerals, Omega-3 and -6 fatty acids, and “something else”. All breeds are pooled for the analysis (n = 116). Statistical significance is marked as following *<0.05, **<0.01, ***<0.001.

Figure 7. Personality factors of the case and control dogs.

Case dogs have TC_index≥2 whereas control dogs have never chased tail tails (TC_index = 0). a) Factor scores (±SE) of cases and controls (all breeds pooled, n = 110) for each of the four factors labelled as Boldness (Shyness/Boldness), Sociability-D (sociability towards dogs), Amicability-H (friendliness towards humans), and Aggressiveness-H (aggressiveness towards humans). b) Factor scores (±SE) of cases and controls (all breeds pooled, n = 110) separately for females and males for two factors labelled as Boldness (Shyness/Boldness) and Aggressiveness-H (aggressiveness towards humans). Note that in the factor Aggressiveness-H, the higher the score, the less aggressive the individual is. Statistical significance is marked following *<0.05, **<0.01, ***<0.001.