4-Propylaminobenzoic acid (PABA) is a strong inhibitor of methanopterin, a key cofactor in the methanogenesis enzymes. From what you have learned about the cow rumen ecology, can you explain why it made cows sick after it was fed to cows? What are your thought about the attempts to reduce methane production from the cattle by feeding the cow with chemical inhibitors of methanogenesis? Please explain the roles of microorganisms in the rumen ecosystem.