Uric acid

Uric acid is what reptiles and birds excrete. It is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates. Uric acid is a product of the metabolic breakdown of purine nucleotides. 
High blood concentrations of uric acid can lead to gout. The chemical is associated with other medical conditions such as diabetes, hypertension, and the formation of kidney stones (ammonium acid urate).