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L. Domenis, D. Marchis, S. Squadrone, M.C. Abete
Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d’Aosta, Italy
C.Re.A.A - National Reference Centre for the Surveillance and Monitoring of Animal Feed
NRL for animal proteins in feeding stuffs

Directive 2003/126/EC defines the rules for the identification of constituents of animal origin in animal feeding stuffs. A skilled and experienced microscopist is required to perform a correct examination and to differentiate between mammalian and poultry bones, which is done examining the characteristics of the bone particles, as fragment colour and outline, osteocyte lacunae shape and density. Since the examination is visual, the results depend on the analyst's knowledge of various features of the ingredients and the application of the microscopic techniques. Several of these features in land animals’ materials (i.e. poultry and mammals) are not always distinguishable, especially the osteocyte lacunae shape that some Authors describe elliptic in poultry and roundish in mammals. The aim of this study was to give a precise description of the characteristics of lacunae in  different chicken bones. For that, smashed fragments and histological sections of the same bone have been compared in order to evaluate the microscopic aspect of lacunae in different breaking and trimming planes.
According to the observations carried out, it’s possible to infer that chicken bone lacuna (as it happens in the man) has nearly a biconvex lens shape. This morphology seems to be maintained in all skeleton; however  the different arrangement and some size variation of the lacuna in the various bone segments influence the microscopic features. Chicken bone is made of a parallel-fibered tissue, without osteons. This distinctive structure probably determines the plane fracture of the bone  and consequently the different microscopic aspect of lacunae (from spindle-shaped to elliptic-roundish). For example, in the fragments from the smashed diaphysis, the prevalence of spindle-shaped lacunae is depending to the preferential breaking of the bone along longitudinal plane. Likewise, the epiphysis, being made mostly by bone trabeculae with strange directions, break along different planes, showing lacunae of various aspect.
Through the official check of animal feed, the presence of bone fragment with roundish, branched lacunae generally induces the analyst to thinking that the meat-bone meal comes from mammals. Although this conclusion is often right, it’s important to consider that also in the chicken it’s possible to find similar aspects, caused by the type and the breaking of the involved bone segments.

Keywords:
Chicken, bone, osteocyte lacunae.