Session 3
Open formulation: perspective of classical microscopy ?

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M.Sc.(Agric) Jan Sten Jørgensen
The Danish Plant Directorate, Lyngby. Denmark

Provisions: Dir. 2002/2/EC states the rules for the labelling of compound feedingstuffs to ensure that stock farmers are informed objectively and as accurate as possible. Feed materials shall be listed by their names and in descending order by weight %. A tolerance of + 15% of the declared value is permitted. The possibility for costumers to get exact information on request was declared invalid by the Court of Justice, and the Directive was amended by decision 623/2007/EC. The feed legislation is for the moment under revision. The issue “open formulation” is reviewed, taking into account the interest of farmers (detailed information) and the interest of the industry (ensure business secrets)

Microscopy method: As an examination method, microscopy of animal feed has been carried out in many European Countries for decades. In Europe microscopists from official control institutes and private laboratories are organised in the organisation “International Association of Feedstuff Analysis – Section Feedstuff Microscopy, but other organisations exists (ex. in United States). The task of the IAG is mainly to develop methods, providing ringtest and exchange of skills and experience. An ongoing challenge for feed microscopists is to keep informed of new products and by-products.

Basic procedure – Identification: Feed materials are identified by their specific macro- and microscopic features. Specific sample preparation is used and micro chemical tests and use of colouring reagents may be used to help identification. Usually more than one feature is used for a reliable identification. Most commonly specific cell structures, presence of vegetable hairs, starch grains and cell crystals are used for identification. Some products may be difficult or even impossible to identify (ex. oil and fat, molasses, milk products, certain precipitated protein concentrates, hydrolyzed and strong heat treated products)

Basic procedure – quantification: Semi quantitative quantification can be made by both sorting and weighing (time consuming) or by a visual estimation. Quantitative values are rounded in increments of usually 5 percentage points. A values of less than 2% is documented as traces.

Quantification uncertainty: Based on extensive ring trials conducted by IAG uncertainty intervals have been developed.

Microscopy advantage/disadvantage