ComparaÃÃo entre tÃcnicas para a determinaÃÃo do clearance ruminal de Ãcidos graxos volÃteis / Comparison between techniques for determination of volatile fatty acids ruminal clearance




Removal (clearance) of volatile fatty acids (VFA) from rumen occurs by rumen wall absorption or by passage to omasum incorporated to ruminal the liquid phase. The objective was to compare measurements of clearance fractional rates obtained by the Hval-Co technique with measurements obtained from 13C labeled VFA. The exponential drop of 13C/12C proportion after 13CAcetate, 13C-Propionate or 13C-Butyrate rumen infusion was used for clearance determination for the 13C technique. The Hval-Co technique was based on exponential drop of ruminal valerate concentration after addition of 300 grams of valerate to ruminal content. Thirty grams of Co-EDTA was mixed to ruminal content in addition to other markers and the fractional rate of cobalt clearance was assumed as VFA ruminal clearance by passage with liquid phase. Each labeled VFA and unlabeled valerate was mixed to evacuated ruminal content of six Holstein-Friesian cows in two 3X3 latin square design. VFA clearance by passage to omasum incorporated to the liquid phase was about 50% from the total clearance, demonstrating that clearance by passage is as important as clearance by rumen wall absorption. Clearance fractional rates were not affected by infused VFA chain length (P>0,21 for VFA type effect). Absorption fractional rates were different among VFA (P<0,03) and propionate had absorption fractional rate higher than butyrate. Linear regression determination coefficients using valerate clearance fractional rate as estimator for acetate, propionate and butyrate ruminal clearance were 0,51, 0,56, and 0,99, respectively. Clearance fractional rate of all VFA was about 30% h-1. Absorption fractional rate ranged from 14 to 19% h-1 according to VFA type. In a second experiment, the 13C-Valerate clearance fractional rate estimative of was similar to that obtained from unlabeled valerate by the Hval-Co technique. These data were obtained from six cows in which VFA clearance was measured by both techniques, simultaneously. There was no ruminal microbial 13C enrichment four hours after 13C-Valerate intraruminal infusion. VFA absorption fractional rate estimates obtained from the stable isotopes technique was similar to that obtained from Hval-Co technique, although both of them had been lower than estimates reported in the literature by other methods.


taxa fracional volatile fatty acids passage zootecnia cattle Ãcido graxo volÃtil fatty acids isÃtopo estÃvel gado leiteiro rÃmen clearance rumen absorÃÃo acidose fractional rate clearance absorption stable isotopes passagem

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