Role of Choline in the Nutrition of the Rumen Protozoon Entodinium caudatum

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Abstract
A requirement of choline for the growth of E. caudatum in a simplified culture medium was demonstrated. Ethanolamine, N-methylethanolamine, or N-dimethylethanolamine were ineffective as substitutes. In the rumen, the normal environment of this organism, levels of free choline were virtually zero even after ingestion of pasture containing phosphatidylcholine which was rapidly catabolized. Free [Me-14C]choline was very rapidly cleared from rumen fluid, a little being incorporated into the phosphatidylcholine of protozoa, but the clearance also occurred in animals [sheep] with defaunated rumens. E. caudatum probably obtained choline for growth mainly from plant membrane material which it had ingested, rather than from the free base in the rumen liquor.