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This article (open access) discusses some of the current challenges in testing animal feed for compliance with European legislation using microscopy (one of the official methods mandated by the legislation).

Although the article is pre-publication and not peer-reviewed, it is generously illustrated with colour photographs of microscope slides - such as that shown here - which could be a valuable training aide to Official Control analysts who are relatively new to microscopy.  The author discusses key areas where expert interpretation is needed, describing the examples of bovine spray-dried plasma protein (legal, within restrictions, in the US but banned in the EU in ruminant feed), differentiating milk powder from blood powder, and differentiating hydrolysed proteins from vegetable vs animal sources.

There is a growing market for the use of insect protein in feed.  The cricket species Gryllus assimilis. is approved in the EU for feeding farmed animals whilst the closely-related G. locorojo is only permitted for pets. The two are difficult to distinguish analytically in a highly processed product.

This paper (purchase required) reports a method developed on the basis of the cytochrome oxidase I gene, (COI), which was sequenced with thoroughly characterised G. locorojo and G. assimilis samples. The method is highly sensitive, detecting 0.8 pg G. locorojo-DNA or 0.1% G. locorojo incurred in feed, respectively. Authentic G. assimilis specimens were used to ensure that the G. locorojo method (Gloco-PCR) discriminates this closely related sister taxon, with a comfortable Ct-difference of 10-15. For cross analysis of true G. assimilis, similar primers with another probe were employed (Gassim-PCR) and the annealing temperature was increased from 60 °C to 62 °C.

Under these conditions, authentic G. assimilis crickets were detectable with Ct-values around 20, while G. locorojo samples showed a low detection at cycles around Ct 35. An investigation of ten ‘G. assimilis’ samples collected from Germany and four other European countries revealed that all of them were of the G. locorojo type.

The authors conclude that this small preliminary survey proves the usefulness of the method and supports the assumption that many G. assimilis crickets marketed in the EU indeed belong to the species G. locorojo. Consequently, European legislation, currently based on a white list of allowed insect species, is critically questioned.

Photo by Ivan Ivanovič on Unsplash