Glucosamine for Dogs is usually extracted from the shells of shellfish (Lobster, crab, crawfish, shrimp, etc.).
The primary technique for making the best selling form of glucosamine is as follows:
This is just one process for manufacturing one of the Glucosamine forms. The three primary forms of glucosamine are glucosamine sulfate, glucosamine hydrochloride and n-acetyl glucosamine. Due to the differences in chemistry, the production process of each will be slightly different.
Proposal for making a “Substantial Equivalence” notification for Non-Shellfish Glucosamine Hydrochloride under Regulation (EC) No 258/97 for the European Parliament and of the Council of 27 January 1997 concerning novel foods and novel food ingredients., Cargill Acidulants, February 5, 2004.
Preparation Of Glucosamine Hydrochloride - Patent 6486307, DocStoc (accessed 4/2012)