Animal feed analysis using microcopy

Since the appearance of mad cow disease (BSE), most of the animal feeds sold or produced in Switzerland are officially and systematically tested for contamination with animal by-products. The method of analysis consists in fractionating (sedimenting and sieving), followed by coloration and observation under the microscope. Particles of animal origin are recognized by their color, form and characteristic structures. This method makes it possible to detect traces (< 0,1 %) of animal compounds and to distinguish between fish and land animal matter if fragments of bones or other mineralized particles are present. Micrographs are made to demonstrate the presence of bone and muscle fiber particles as well as other typical parts of fish or other vertebrates. Results of controls from 1991 to 2002 show that the proportion of positively tested samples for fragments of land animal bones has markedly decreased, at the same time, the number of analyzed samples has increased, particularly since 2001.At present, microscopy is the fastest, cheapest and most accurate method to analyze the presence of animal by-products in animal feeds.