Microscopic examination of dog chews: correlation of histological findings to product labeling

The purpose of this study was to use routine morphologic-based staining techniques to examine the histology of commercially labeled rawhide and rawhide-free dog chew products and compare the results to the product labeling. Ten dog chew products were examined by light microscopy using hematoxylin and eosin and Masson's trichrome stains. The products were labeled by the manufacturer as rawhide, beef hide, beef chew/rawhide free, and rawhide free. Four of the products were composed of two separate materials, a main chew roll and a second substance (filler) which was coated on or between the layers of the main chew roll. These materials were processed independently. Microscopically, a variety of tissues and materials were identified including collagen, skeletal muscle, fat, plant material, and starch. The products and their fillers were separated into four distinct groups based on microscopic appearance. The components identified in eight of the products appeared consistent with the product labeling. Two products labeled as rawhide free appeared similar to the dermis and this was inconsistent with product labeling. Masson's trichrome stain was not helpful in distinguishing tissue types in the tested products and this may have been due to the heat processing the products underwent during manufacturing. Bacteria and/or fungi were identified by microscopy in the H&E stained sections in four rawhide-free products.