In late-pregnant Yili mares, daily supplementation with 30 grams of L-citrulline significantly increases plasma concentrations of citrulline and arginine by over 50% and elevates ornithine, histidine, leucine, and glutamate, indicating enhanced flux through the urea cycle and improved amino acid metabolism.

When L-citrulline is taken, it enters the bloodstream and goes to the kidneys, where it is turned into arginine. This arginine then fuels the urea cycle, which pulls ammonia out of the blood and turns it into urea for safe removal. More arginine also leads to higher levels of ornithine, glutamate, histidine, and leucine, because the cycle produces these amino acids as part of its normal flow. The body uses this improved cycle to make more protein and reduce harmful ammonia buildup.