Bioactive Collagen Peptides in Veterinary and Biomedical Science—Part I: Molecular Identity, Gastrointestinal Bioavailability, and Receptor-Mediated Signaling, with Relevance to the Bile Acid Axis
Simple Summary Collagen is the main structural protein of skin, bone, tendon, and cartilage, and it was long viewed only as a building material. When collagen is broken into small fragments—during digestion or in collagen supplements—some fragments are absorbed into the blood and act as signals that influence the body well beyond the tissues they came from. This review, the first of two parts, examines what these small collagen fragments are, how efficiently animals absorb them, and which cell-surface sensors and internal pathways they switch on. The evidence comes from laboratory experiments, animal studies, and clinical trials, and we are careful throughout to separate firm clinical findings from early laboratory observations. The strongest current evidence supports specific collagen fragments for relieving joint disease in dogs and horses. We also describe a newly recognised link between collagen fragments, gut bacteria, and bile that may explain effects on metabolism and the liver. The main message for practice is that collagen supplements are biologically active compounds whose effects differ between species, so the dose and the expected benefit should be judged species by species rather than assumed from one animal to another.