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Spectroscopy aids determination of birds’ sex

BioPhotonics
Mar 2008
Michael J. Lander

As a visit to the zoo reveals, some bird species display marked sexual dimorphism, with males bearing colorful plumage and females a drab, unadorned coat. But juvenile birds and birds of certain species, such as parrots, may carry no outward sign of their sex. For positive identification, breeders and poultry industry workers often must take blood samples or anesthetize the birds and look for internal gender cues through an endoscope. Although effective, these methods prove costly and may injure the animals. An optically based technique, however, could offer a minimally invasive solution.

Jürgen Popp of Friedrich Schiller Universität Jena and colleagues from Universität Leipzig, both in Germany, have employed spectroscopy to permit sexing using a small feather removed gently from a bird’s body.

BNbird_-Schematic.jpg

The diagram shows how researchers extracted chicken feather pulp samples and demonstrates the spectroscopic setup used to analyze them. Courtesy of Jürgen Popp, Friedrich Schiller Universität Jena.

Specifically, the scientists’ procedure relied on analysis of the pulp tissue found within the shaft of avian contour feathers. Pressing the pulp from the feathers of 18 male and 16 female chickens and spreading it on fused-silica wafers, the researchers focused a Coherent argon-ion laser emitting at 244 nm on the samples with a broadband UV objective. A Horiba Jobin Yvon micro-Raman spectroscope recorded the spectra, and a nitrogen-cooled CCD camera collected the scattered light and fed the data to a computer.

Raman spectra

For assigning gender based on differences in the UV-resonance Raman spectra, the investigators chose the support vector machine method, which is widely used for biological classification. To establish the key wavelength regions exhibiting the most significant variation between males and females, the group employed principal component analysis.

Inspection of spectra in the wave number region between 600 and 1800 cm–1 revealed higher band intensities for samples from males, mainly the result of higher DNA content in their cells than in those of females. Comparison with spectra for purified DNA and for protein samples clarified the origin of observed peaks. Precise statistical differences calculated with the support vector machine technique permitted correct identification of the birds’ sex in 95 percent of cases. From the principal component analysis, the researchers determined that seven regions between 1660 and 1336 cm–1 were essential for differentiation.

Compared with vent sorting, a widely used manual procedure performed by squeezing chicks to reveal their internal sexual organs, the Raman spectroscopy technique displayed roughly the same accuracy. The researchers’ method also takes less than a minute from start to finish — less time than endoscopic, blood sample-based and molecular biological sexing procedures. With a calibrated setup, an individual can perform determinations with minimal training and little risk of injury to the animals.

According to Popp, the greatest application of the technology may exist in the chicken and turkey industries, where a bird’s gender determines its usefulness. In egg production, for example, he said male chicks have no place and often are killed before maturity to reduce costs associated with raising them. To this end, the researchers’ next goal comprises creating a device capable of sexing through the egg prior to hatching, a more humane and efficient option.

Popp said that the team also intends to reduce the size of the device because samples require transportation to a laboratory. At about 5 kg, the target unit could enable rapid in-field gender determination.

Analytical Chemistry, Feb. 15, 2008, pp. 1080-1086.


GLOSSARY
endoscope
A medical instrument used to view inside the human body by inserting the instrument into a natural or created aperture. The endoscope may use a coherent fiber optic bundle or conventional optics to relay the image to the eye or a television camera. Illumination is provided by a concentric bundle of noncoherent fiber optics.  
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