title: Comparison of techniques to determine the clearance of ruminal volatile fatty acids.
abstract: The objective of this experiment was to compare measurements of fractional clearance rates obtained by using an unlabeled valerate-CoEDTA technique with measurements obtained by using a (13)C-labeled volatile fatty acids (VFA) technique. The exponential decay rate of the (13)C/(12)C ratio after pulse-dosing (13)C-acetate, (13)C-propionate, or (13)C-butyrate into the rumen was compared with the decay rate of rumen valerate concentration following a simultaneous pulse dose. The unlabeled valerate, CoEDTA, and each labeled VFA, one at a time, were concurrently mixed with the evacuated ruminal content of 6 lactating cows in two 3 x 3 Latin squares. The clearance of VFA by passage to the omasum was assumed to be equivalent to the decay in ruminal Co concentration and was around 50% of the total clearance. Acetate, propionate, and butyrate had similar fractional clearance rates (31.2, 33.4, 30.4%/h, respectively), but propionate had a higher absorption rate (19.2%/h) than butyrate (14.2%/h). Linear regression determination coefficients using the valerate clearance rate as an estimator for acetate, propionate, and butyrate rumen clearance were 0.51, 0.56, and 0.99, respectively. In a second experiment, the (13)C-valerate fractional clearance rate estimate (33.7%/h) was similar to the estimate obtained with unlabeled valerate (35.0%/h) by the valerate-Co technique. No (13)C enrichment of rumen microbes was noted 4 h after the intraruminal infusion of (13)C-valerate. Fractional VFA absorption rate estimates obtained in both techniques were similar, although both were lower than estimates reported in the literature by other methods.
authors.affiliation: Departamento de Medicina Veterinária, Universidade Federal de Lavras, Lavras, MG, Brazil, 37200-000. joaocrj@ufla.br
authors.forename: J C
authors.initials: JC
authors.lastname: Resende Júnior
authors.forename: M N
authors.initials: MN
authors.lastname: Pereira
authors.forename: H
authors.initials: H
authors.lastname: Bôer
authors.forename: S
authors.initials: S
authors.lastname: Tamminga
mesh_terms: D000042:Absorption; D000085:Acetates / Q000378:metabolism; D000818:Animals; D001826:Body Fluids / Q000737:chemistry; D002087:Butyrates / Q000378:metabolism; D002247:Carbon Isotopes; D002417:Cattle / Q000378:metabolism*; D004492:Edetic Acid / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000032:analysis / Q000378:metabolism* / Q000493:pharmacokinetics; D005260:Female; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D007700:Kinetics; D007774:Lactation; D016014:Linear Models; D008657:Metabolic Clearance Rate; D011422:Propionates / Q000378:metabolism; D012417:Rumen / Q000378:metabolism*; D014631:Valerates / Q000378:metabolism
chemical_list: D000085:Acetates; D002087:Butyrates; D002247:Carbon Isotopes; D005232:Fatty Acids, Volatile; D011422:Propionates; D014631:Valerates; C028222:cobalt-ethylenediamine tetraacetic acid chelate; D004492:Edetic Acid