AvaliaÃÃo morfofisiolÃgica da absorÃÃo e metabolizaÃÃo de Ãcidos graxos volÃteis pelo proventrÃculo de bovinos. / Morphophysiologic evaluation of the absorption and metabolism of volatile fatty acids by bovine forestomach.




About 60% of volatile fatty acids (VFA) produced in reticulorumen are absorbed in this compartment. The other 40% pass with the fluid phase to the omasum and are absorbed before entering the duodenum. Two experiments were carried out to determine the absorption surfaces and the VFA absorption and metabolism capacity of the bovine forestomach compartments. In the first experiment, the absorption surfaces of the forestomach compartments of the eight adult bovines were measured through image capture and analysis. The reticulorumen absorptive surface (7.7 m2) was larger than the omasum absorptive surface (2.1 m2). The surface/digesta ratio, however, was larger in the omasum (0.31 m2/kg) than in the reticulorumen (0.13 m2/kg), representing an omasum surface for each digest unit 2.4 times larger. The absorption surface/wall surface ratio of one rumen ventral sac fragment showed a positive and high correlation (r = 0.84) with the total rumen surface, indicating that it is possible to estimate the rumen surface by biopsy. In the second experiment, the VFA absorption and metabolism capacities of the rumen and omasum were compared, in vitro. After the slaughter, fragments of the rumen wall and omasum laminae were taken from eight adult crossbred bovines. An isolated fragment of the mucosa was fitted in a tissue diffusion chamber. Valeric acid and CrEDTA were added to the ruminal fluid and placed on the mucosal side. Krebs-Ringer bicarbonate buffer solution was placed on the serosal side. The absorption surface of the rumen fragment (57.6 cm2) was higher than that of the omasum (4.9 cm2), because of the ruminal papillae. The mitotic index of the omasum (0.52%) was higher than that of the rumen epithelium (0.28%). The VFA fractional absorption rate was higher in the omasum (4.6%.h-1.cm-2) than in the rumen (0.4%.h-1.cm-2). Acetate, propionate, butyrate and valerate showed similar fractional absorption rates in both fragments. The percentage of metabolized acetate (10.9%) was lower than propionate (31.1%) which was lower than butyrate (39.8%) and valerate (42.0%). The correlation between VFA metabolism and mitotic index was positive, but the VFA absorption was not correlated with other variables in the rumen. In the omasum, the correlation between VFA absorption and mitotic index was positive, however, those variables were negatively correlated with the VFA metabolism. Despite the reticulorumen absorption surface being higher than that of the omasum, the VFA metabolism and absorption potential of the omasum is higher than the reticulorumen. The rumen and omasum absorption capacities vary in the same way, and there are indications that the factors capable of stimulating the rumen wall are also capable of stimulating the omasum wall proliferation.


absorption rumen valerato absorÃÃo rÃmen mitotic index omasum ruminant stomach bovino proventrÃculo volatile fatty acid estÃmago de ruminante valerate Ãcido graxo volÃtil omaso bovine absorptive surface superfÃcie absortiva forestomach cÃmara de difusÃo tecidual metabolismo medicina veterinaria tissue diffusion chamber Ãndice mitÃtico metabolism

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