Marker concentration patterns of labelled leaf and stem particles in the rumen of cattle grazing bermuda grass (Cynodon dactylon) analysed by reference to a raft model

Large (>1600 mum), ingestively masticated particles of bermuda grass (Cynodon dactylon L. Pers.) leaf and stem labelled with Yb-169 and Ce-144 respectively were inserted into the rumen digesta raft of heifers grazing bermuda grass. The concentration of markers in digesta sampled from the raft and ventral rumen were monitored at regular intervals over approximately 144 h. The data from the two sampling sites were simultaneously fitted to two pool (raft and ventral rumen-reticulum) models with either reversible or sequential flow between the two pools. The sequential flow model fitted the data equally as well as the reversible flow model but the reversible flow model was used because of its greater application. The reversible flow model, hereafter called the raft model, had the following features: a relatively slow age-dependent transfer rate from the raft (means for a gamma 2 distributed rate parameter for leaf 0.0740 v. stem 0.0478 h(-1)), a very slow first order reversible flow from the ventral rumen to the raft (mean for leaf and stem 0.010 h(-1)) and a very rapid first order exit from the ventral rumen (mean of leaf and stem 0.44 h(-1)). The raft was calculated to occupy approximately 0.82 total rumen DM of the raft and ventral rumen pools. Fitting a sequential two pool model or a single exponential model individually to values from each of the two sampling sites yielded similar parameter values for both sites and faster rate parameters for leaf as compared with stem, in agreement with the raft model. These results were interpreted as indicating that the raft forms a large relatively inert pool within the rumen. Particles generated within the raft have difficulty escaping but once into the ventral rumen pool they escape quickly with a low probability of return to the raft. It was concluded that the raft model gave a good interpretation of the data and emphasized escape from and movement within the raft as important components of the residence time of leaf and stem particles within the rumen digesta of cattle.

Osaamiskeskittymien uusia kehityssuuntia

Kirjallisuusarvostelu

[7-8-20, bassin de la Villette, championnat de France militaire de natation], Duravanel [i. e. Henri Duvanel], Mayaud [nageur de Joinville, ex-aequo du 300 m nage libre] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 60398

Didáctica de la educación infantil.

Trabajo que presenta un modelo educativo integrador a varios niveles: expresivo, sensorial-psicomotor, relacional-social y cognitivo. Seguidamente se recoge una síntesis de las características del niño de esta edad y, a partir de aqui, se aborda el estudio de la función de la escuela infantil, el concepto de educación infantil, el currículo, los objetivos, la organización del espacio-aula, los contenidos, las actividades y experiencias, concediendo gran importancia al aspecto lúdico..