I hope that breeders and those with any interest in behavioral issues in Nihon Ken are following and taking notice of Dr. Yukari Takeuchi’s work (武内 ゆかり, DVM, PhD). Takeuchi is at the University of Tokyo’s Laboratory of Ethology, and has done extensive research on genetic linkages and manifestations of aggression by breeds, with special attention to native Japanese breeds like the Akita and Shiba Inu.
In a 2006 report surveying a broad range of breeds, “A Comparison of the Behavioral Profiles of Purebred Dogs in Japan to Profiles of those in the United States and the United Kingdom,” Shiba were found to be ranked higher than average in aggressive behavior towards other dogs, watchdog barking, territorial defense, and snapping at children. They were clustered in a group known to have “high aggression, high reactivity, and medium trainability” along with the likes of Pomeranians, American Cocker Spaniels, Yorkshire Terriers, Irish Setters, Maltese, Pugs, Mini Schnauzers, Mini Dachshund, and others. The tag “medium trainability” says to me that Shibas may potentially have these unfavorable behaviors trained out of them, bringing home the point that socialization is key.
In another article from 2009, “Association analysis between canine behavioural traits in the Shiba Inu and genetic polymorphisms,” (Takeuchi Y, Kaneko F, Hashizume C, Masuda K, Ogata N, Maki T, Inoue-Murayama M, Hart BL, Mori Y, Animal Genetics 40: 616-622), what I understood was that there are tentative causal links between certain genes and Shiba aggression. However, because there are many social factors that contribute to aggression, as well as many ways to define aggression, more research needs to be done.
It was also noted that the Shibas surveyed were all from Japan, where many are still kept as watchdogs, particularly in rural areas. In such cases, certain types of “aggression” as noted in the 2006 study are favorably linked to their function.
In the meantime:
The reasons and motivations for having dogs vary from owner to owner; some want a watchdog for security while others desire a companion for family members. If veterinarians working at clinics know the behavioral profiles of purebred dogs and the tendencies in gender differences shown in this  study, they can more appropriately advise prospective owners. This can facilitate a better quality of human-animal bond and perhaps prevent behavioral problems due to a mismatch between dogs and owners. In addition, veterinarians should inform potential owners of the importance of understanding the pedigree line within a breed, the behavior of the dam, sire, and siblings from previous litters, and the early environment during the socialization period, as has been repeatedly emphasized in previous studies (p. 7 of the 2006 study).
Takeuchi seems to consider veterinarian expertise the first line of defense against uninformed dog owners acquiring a potentially volatile breed. This statement stems from his methodology, wherein he asked veterinarians to answer based on their familiarity with the breeds surveyed, instead of breeders and purebred dog owners. In practice, I doubt most owners consult with a veterinarian before bringing home their dog; you usually get the dog first, then bring him to the vet. But his very efforts to find a genetic basis for aggression is intriguing nevertheless. If such a clear, direct genetic factor could be located, this would put a lot more weight on the selective breeding of purebred dogs, as well as throw open a whole set of related cultural issues on why breeders select for the temperaments and the individual dogs that they do.
I also find it interesting that a number of breeds considered to be “highly aggressive” also rank relatively highly on the Michigan State University’s charts for breeds at risk for thyroid disorders. Specifically, I’m looking at Maltese (#9, 16.5% autoimmune thyroiditis), Beagles (#10, 16.5%), Dalmatians (#11, 16.3%), Cocker Spaniels (#13, 15.7%), Irish Setters (#25, 12.6%), all grouped in the same cluster as Shiba Inu. In another cluster of dogs with “high aggression, low reactivity, high trainability,” there are breeds like the Boxer (#6, 18%.0), Great Dane (#36, 10.1%), Akita (#46, 8.6%), and Doberman Pinscher (#50, 8.4%). A lot of the smaller breeds rank pretty far down the list, like Yorkies and Pomeranians, which matches what I understand about hypothyroidism usually affecting medium to large-sized dogs.
But the notable overlaps make me wonder if a statistical correlation between breeds documented to be “aggressive” and thyroid disorders could be made even clearer by someone else with more rigorous analytical methods. While there is a lot of online and anecdotal information about hypothyroidism as an underlying factor contributing to aggression and behavioral changes in dogs (I’m thinking in particular about the work of Dr. Jean Dodds who presented her findings at the 1996 International Symposium on Canine Hypothyroidism), American DVMs seem to downplay the link between hypothyroidism and aggression, and there hasn’t been much published information in peer-reviewed journals echoing Jean Dodd’s findings.
Considering that 1996 wasn’t that long ago, in my mind, and that was the first (and only!) large-scale conference on canine hypothyroidism to have appeared in my searches, I bet more work can still be done. I just hope the specialists are talking to each other, and not content to let endocrinologists do their own thing, while ethologists do their own thing, and dermatologists and neurologists and hematologists and so forth are not limiting themselves to the information immediately at hand.