Preliminary Forensic Study of Hair Morphology and Micrometry of Small-Sized Dog Breeds

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Hong Kong, located in Southern China, is one of the world's most densely populated cities. Although dealing with the challenge of living in small spaces, more and more families are keeping pets. Pet ownership has undergone exponential growth as nearly 241,900 Hong Kong households (i.e., 9.4 % among all households) had pets at home, while the number of pet dogs and cats increased from 297,100 in 2005 to 405,200 in 2018. Dogs possess hair that is easily shed, thus has great chances to be found at a crime scene through primary or secondary transfer. As every contact leaves a trace, examination of dog hair to identify dog breeds may establish a link between suspect, victim and a crime scene as associative evidence. Previous studies on the morphology and micrometry of dog hair investigated large-sized dog breeds, such as Husky, Rottweiler and Doberman, while these dog breeds are not common in Hong Kong. This was the first study to investigate the morphological and micrometric differences among hair collected from small-sized dogs that are commonly found in homes with small living spaces. Hair samples were collected from popular small-sized dog breeds in Hong Kong such as Poodle, Shiba Inu, Miniature Schnauzer and Pomeranian. With a scanning electron microscope and a compound microscope, morphological (e.g., hair color, cuticle scale pattern and medullary pattern) and micrometric characteristics (e.g., hair shaft diameter, medulla diameter, medullary and cuticular indices) were determined. Distinctive cuticle scale pattern was observed: elongate petal in Shiba Inu and coronal in Poodle, while these arrangements were rarely found in large-sized dog breeds that were reported in previous studies. Hairs of Shiba Inu also showed the medulla to be uniserial ladder, which could be considered a distinctive characteristic of this breed. The findings from this preliminary study are useful for forensic investigations to differentiate and identify small-sized dog breeds through hair sampling. Further studies involving larger numbers of small-sized dog breeds and subjects will be carried out.