Cell counts and quantities of human DNA on dog hairs

Animal hair DNA analysis has been well documented and, in general, address both species identification and geographic origin. Little attention has been given to the detection of human DNA. This preliminary study evaluated the use of Diamond™ Nucleic Acid Dye to estimate the cellular content on the hair samples of three patted dogs and the predictive value of these cell counts for subsequent DNA analysis. Targeted cell counts of 500, 1000 and 5000 cells were analysed. Number of hairs, hair length and quantity of DNA were analysed to determine how many dog hairs are needed to produce a human DNA profile. Quantifiable DNA was detected in 89% of the hair samples and DNA profiles were generated from 78% of those. Many of the hair samples (44%) provided ≥12 alleles that can produce high-value inclusionary Likelihood Ratios, if reference samples are available. Furthermore, 14% of the profiles were suitable for database upload highlighting the potential value of these samples. However, the predictive power of cell counts was limited in this study. Where relevant, e.g. when an animal is suspected to have been involved, recovery of human DNA from animal hairs at a scene may be of value during investigations.