My vet recommended Cosequin DS. It also contains Condroitin (sp?) and I do believe it helped my old girl. The human Glucosamine is made from shellfish, the dog version is not. Only problem there might be allergies, and the Cosequin is a beef flavored chewable. 1500 is a good number for the Glucosamine.
While it is possible to have "vegetarian based" or Shellfish-Free Glucosamin Cosequin DS is not that product. If your pet has a shellfish allergy you might want to look at Jointinol-v™ Vegetarian Glucosamine Formula.