Chewable Collagen Treat For Dogs Chewllagen is made of natural collagen & dipped in real Beef or Chicken. Chewllagen is made of collagen, which is extracted from a cows hide by method of heat. Collagen is natural and found within the skin. Once the collagen is extracted its processed into different shapes and then placed in to the oven for drying. When completely dried its then dipped in Beef or Chicken and place back in the oven for finishing off to obtain the finish product.