title: Rumen fermentation in vitro as influenced by long chain fatty acids.
abstract: Responses of rumen microbes to fatty acids were evaluated by production of total volatile fatty acid and ratio of acetate to propionate. Fermentations were under carbon dioxide for 20 h in 50-ml Erlenmeyer flasks in a Dubnoff metabolic shaking incubator. Flasks contained 20 ml medium, 1 ml reducing solution, 750 mg substrate (450 mg hay plus 300 mg grain), and varying amounts of long-chain fatty acids supplied as free acids, as calcium salts, or as triglycerides. They were inoculated with 5 ml rumen fluid obtained from a cow fed 3.6 kg grass hay, 2.3 kg grain, and .2 kg tallow daily. Volatile fatty acid production was decreased by long-chain fatty acids that contained less than 18 carbon atoms and by unsaturated long-chain fatty acids with 18 carbon atoms. Lauric acid decreased volatile fatty acid production by 69% and induced unusual acetate/propionate ratio (40:1). Stearic acid, however, did not affect volatile fatty acid production or acetate/propionate ratio. Within two series of long chain fatty acids (myristic, palmitic, stearic, arachidic; stearic, oleic, linolenic), melting point accounted for 93 to 95% of the variation of volatile fatty acid production and acetate/propionate. As calcium salts, long chain fatty acids caused small changes of fermentation. Our data support the proposition that hard fats and calcium salts of long-chain fatty acids do not interfere with ruminal fermentation.
mesh_terms: D000085:Acetates / Q000096:biosynthesis; D019342:Acetic Acid; D000818:Animals; D001419:Bacteria / Q000187:drug effects* / Q000378:metabolism; D002417:Cattle; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D005232:Fatty Acids, Volatile / Q000096:biosynthesis*; D005285:Fermentation / Q000187:drug effects; D066298:In Vitro Techniques; D011422:Propionates / Q000378:metabolism; D012417:Rumen / Q000378:metabolism*
chemical_list: D000085:Acetates; D005230:Fatty Acids, Nonesterified; D005232:Fatty Acids, Volatile; D011422:Propionates; C029658:propionic acid; D019342:Acetic Acid