Evaluation of the serotonergic genes htr1A, htr1B, htr2A, and slc6A4 in aggressive behavior of golden retriever dogs.

Aggressive behavior displays a high heritability in our study group of Golden Retriever dogs. Alterations in brain serotonin metabolism have been described in aggressive dogs before. Here, we evaluate whether four genes of the canine serotonergic system, coding for the serotonin receptors 1A, 1B, and 2A, and the serotonin transporter, could play a major role in aggression in Golden Retrievers. We performed mutation screens, linkage analysis, an association study, and a quantitative genetic analysis. There was no systematic difference between the coding DNA sequence of the candidate genes in aggressive and non-aggressive Golden Retrievers. An affecteds-only parametric linkage analysis revealed no strong major locus effect on human-directed aggression related to the candidate genes. An analysis of 41 single nucleotide polymorphisms (SNPs) in the 1 Mb regions flanking the genes in 49 unrelated human-directed aggressive and 49 unrelated non-aggressive dogs did not show association of SNP alleles, genotypes, or haplotypes with aggression at the candidate loci. We completed our analyses with a study of the effect of variation in the candidate genes on a collection of aggression-related phenotypic measures. The effects of the candidate gene haplotypes were estimated using the Restricted Maximum Likelihood method, with the haplotypes included as fixed effects in a linear animal model. We observed no effect of the candidate gene haplotypes on a range of aggression-related phenotypes, thus extending our conclusions to several types of aggressive behavior. We conclude that it is unlikely that these genes play a major role in the variation in aggression in the Golden Retrievers that we studied. Smaller phenotypic effects of these loci could not be ruled out with our sample size.

Phenotyping of aggressive behavior in golden retriever dogs with a questionnaire.

Reliable and valid phenotyping is crucial for our study of genetic factors underlying aggression in Golden Retriever dogs. A mail questionnaire based on the Canine Behavioral Assessment and Research Questionnaire (CBARQ; Hsu and Serpell, 2003, JAVMA 223(9):1293-1300) was used to assess behavioral phenotypes. Owners of 228 Golden Retrievers completed the questionnaire. These dogs had been referred to our clinic for aggression problems several years earlier or they were related to aggressive dogs. In this paper, three sets of results are presented, which indicate that behavior scores from the CBARQ can be applied to genetic studies. First, factor analysis demonstrated that CBARQ items can be grouped into 10 behavioral traits, including three types of aggression: stranger-directed aggression, owner-directed aggression, and dog-directed aggression. The results were remarkably similar to those reported by Hsu and Serpell. The aggression scores showed considerable variation in our dog families, which is a prerequisite for genetic studies. Second, retrospective questions enabled us to study changes in the aggressive behavior of the dogs in the course of time. After an average time interval of 4.3 years, over 50% of the dogs had become less aggressive. Third, we analyzed data obtained with an aggression test of 83 dogs. Two out of the three CBARQ aggression factors were also found in the aggression test data.

Behavior genetics of canine aggression: behavioral phenotyping of golden retrievers by means of an aggression test.

Molecular genetic analysis of complex traits such as aggression strongly depends on careful phenotyping of individuals. When studying canine aggression, the information provided by the owners of the dogs is often not detailed and reliable enough for this purpose. Therefore we subjected 83 golden retrievers, both aggressive and nonaggressive individuals, to a behavioral test. These tests were analyzed with help of an ethogram, resulting in a behavioral profile for each of the dogs. In this article three methods are described of converting these profiles into a measure of behavioral phenotype. The usefulness of the methods is evaluated by comparing the test results with information provided by owners. Moreover, the hypothesis underlying all these methods, that a lowered threshold for aggressive behavior in general is present in the dogs, is also evaluated. Future research will need to reveal whether the methods meet the high standards that are necessary for studying complex traits.

Heart rate and heart rate variability during a novel object test and a handling test in young horses.

Forty-one Dutch Warmblood immature horses were used in a study to quantify temperamental traits on the basis of heart rate (HR) and heart rate variability (HRV) measures. Half of the horses received additional training from the age of 5 months onwards; the other half did not. Horses were tested at 9, 10, 21 and 22 months of age in a novel object and a handling test. During the tests, mean HR and two heart variability indices, e.g. standard deviation of beat-to-beat intervals (SDRR) and root mean square of successive beat-to-beat differences (rMSSD), were calculated and expressed as response values to baseline measures. In both tests, horses showed at all ages a significant increase in mean HR and decrease in HRV measures, which suggests a marked shift of the balance of the autonomic nervous system towards a sympathetic dominance. In the novel object test, this shift was more pronounced in horses that had not been trained. Furthermore, statistical analysis showed that the increase in mean HR could not be entirely explained by the physical activity. The additional increase in HR, the nonmotor HR, was more pronounced in the untrained horses compared to the trained. Hence, it is suggested that this nonmotor HR might be due to the level of emotionality. HR variables showed consistency between years, as well as within the second year. These tests bring about a HR response in horses, part of which may indicate a higher level of emotionality; and horses show individual consistency of these HR variables over ages. Therefore, it is concluded that mean HR and HRV measures used with these tests quantify certain aspects of a horse's temperament.