Proline is an important amino acid for chicken growth, but they can make most of it themselves. Adding more arginine, ornithine, or glutamic acid to their diet doesn't really help. The process of making proline from these amino acids is limited in chickens, and we're not sure why. In bacteria, we know the steps to make proline from glutamate, but we need more research to understand how this works in chickens. Some enzymes in chicken liver and kidney might be involved in proline production, but we need more studies to confirm this.