Identification of chamois through DNA analysis10 January 2005
Summary For the first time, DNA has been extracted and analysed from leather for the purposes of species identification. Working with a partner laboratory using techniques similar to those pioneered for forensic DNA profiling, BLC has determined an exact species identification for a range of leather types including bovine, ovine, caprine and porcine. This will allow the authentication of genuine chamois leather through a positive species identification. The development will also have wider implications in terms of Trading Standards and Customs issues and identifying leathers of historical interest. It is hoped to extend the use of this technique to facilitate ultimate traceability within the supply chain. The genetic fingerprint DNA or deoxyribonucleic acid is the basic genetic material supporting life. It is as unique as a human fingerprint and can be used to identify species and more importantly individuals within a given species. For example, DNA is different for every human being on earth, with the exception of identical twins. DNA profiling or fingerprinting was pioneered in the UK in 1985 by Professor Alec Jeffries. This technique allows minute fragments of DNA (often aged and damaged) to be repaired and replicated in sufficient quantities to be identified. Polymerase chain reaction Small amounts of DNA are copied through a specific reaction catalysed by an enzyme isolated from a bacterium (Thermus aqauticus) originally sourced from a hot spring within the Yellowstone National Park. Using a technique known as the polymerase chain reaction (PCR), the enzyme (DNA polymerase) can produce millions of copies of a single fragment of DNA in a matter of hours through thermo-cycling techniques. This has revolutionised the identification of DNA which previously was not possible due to either low concentrations and/or poor condition of the molecules extracted from biological samples. The extracted DNA is then cleaned and screened using electrophoresis which separates the DNA within an agarose gel inside an electric field. The resulting profile (which can be visualised using an UV indicator) can be compared to standard DNA markers (along with the appropriate controls) to determine absolute identity. The unique properties of DNA, coupled with advances in the extraction and analysis of the molecules has facilitated its use within the field of forensic science to relate scenes of crime evidence such as bodily fluids and hair samples to criminals for identification purposes. The technique was also used for the first time in a legal parental dispute in 1984. Since this time DNA profiling has received other applications including testing for the presence of genetically modified organisms (GMOs) and food authenticity. Chamois leather authenticity The DNA profiling techniques described have been used for the first time to assist with a leather trade related issue. According to the British and US Federal Standards, authentic chamois leather must originate from sheep or lambskin. An issue with traditional species identification using microscopy is the absence of the grain layer, making identification difficult and potentially inaccurate. A recent study carried out by BLC Leather Technology Centre, on behalf of a supplier of chamois leather, has identified that many articles sold as 'genuine' chamois leathers do not meet the legal requirements of this definition in that some products do not originate from sheepskin. The definition listed in BS 2780:1983 is as follows: A) Leather made from the flesh split of sheepskin or lambskin, or from sheepskin or lambskin from which the grain has been removed by frizing and tanned by processes involving the oxidation of marine oils in the skin, using either solely such oils (full oil chamois) or first an aldehyde and then such oils (combination chamois). Note: In the USA, the term 'chamois' without any qualification is restricted to the flesh split of sheep or lambskin tanned solely with oils. B) Leather made from the skin of the mountain antelope or chamois. Under definition A, leathers made from any substrate other than sheep and lamb cannot be marketed as genuine chamois leather. Also any leather that is first tanned and then subsequently fatliquored with marine oils can not be classed as chamois leather. The key problem faced by the industry is the difficulty in proving that cheaper inferior quality products are actually made using inappropriate substrates or are not oil tanned. Testing for authenticity of chamois leather is complicated. The most technically challenging element is proving the origin of species. This is because chamois leather does not have the grain layer present which would facilitate conventional species diagnosis by microscopy. Using microscopy, it is normally possible (although not always definitively) to identify species through analysis of the characteristic grain pattern present on the surface of the leather. Goat skins have a very different hair follicle pattern to sheep. Goat skins are normally arranged in lines of primary and smaller secondary hair follicles. Sheepskins have more uniformly sized hair follicles arranged in groups. First time for genetic testing and leather All species of animal are distinguishable by their characteristic DNA profile, with no two species sharing like DNA. The ability to extract and identify DNA from leather using the techniques described would provide unequivocal species identification (between sheep, goat and pig, for example). To evaluate the DNA profiling techniques for leather, various samples of different leather types were prepared for genetic testing to determine the absolute DNA fingerprint of the sample. This technique has not previously been applied to a leather substrate and the method required extensive development and modification. DNA is a very robust molecule and will survive even extreme conditions. The extensive pH changes associated with leather processing (in particular pickling) can cause damage to the molecules which needs to be corrected within the analytical process. The samples also require an elongated incubation process to sufficiently recover the DNA to facilitate PCR. A range of leather types were tested (including sheep, goat and pig) in addition to three chamois samples (one of which was known to be authentic). After extensive trials, the results obtained show that it is possible to profile leathers to prove their origin, although further work to develop the protocols fully may be required. Initial results are given in Table 1. The results indicate that chamois leathers 1 and 2 are produced from goat rather than sheepskin whilst the genuine chamois was definitely not produced from goat. Subsequent experiments have proven a positive sheep identification for this product. Of the four leathers tested only one was indicative of being genuine chamois. Pushing the boundaries This is an exciting development for the leather industry, using state of the art genetic testing procedures. This study has demonstrated how advanced science can be applied to the leather industry to solve trade issues such as chamois authentication. The potential for a robust and reliable system of species identification within the leather industry is significant. Certain trade issues such as those described with chamois leather could take advantage of this highly specific test. Definitive species testing for the control of protected species may also be a possibility and the identification of sub-species of animals, for example Zebu. Another potential use is the identification of historical leathers and ultimately traceability of leather through the supply chain.