what is collagen peptides made of?

Structurally, collagen peptides are made entirely of amino acids—predominantly glycine, proline, and hydroxyproline. But in terms of raw materials, they are extracted from the connective tissues of animals.
The vast majority of the commercial bulk market is made from bovine hide and bones (cow), which yields an excellent mix of Type I and Type III collagen. The second most popular source is marine scales and skins (fish), which is predominantly Type I. You can also find it made from porcine (pig) skin and poultry (chicken) cartilage, depending on the specific application.