Quantitative aspects of protein and free amino acid metabolism in the rumen

Abstract

A series of in vivo trials were conducted to study the quantitative fate of casein during its degradation in the rumen. A nonlactating cow was maintained in a steady state by hourly feeding of a high concentrate diet. In trials II and VI, the animal was pulse-dosed via a rumen cannula with 200 g casein and 1000 ml .05 M of Cr-DTPA as liquid fraction marker. In control trials III and V, only the marker was dosed. A rumen pump was used to mix rumen contents and to aid in sampling during the first 3 hr of the experiment. Samples of strained rumen fluid (SRF) and whole rumen contents (WRC) were taken frequently immediately after dosing, and less frequently later in the experiment over each 48 hr trial period. Procedures used to stop microbial activity in SRF samples were HgCl(,2) on one set of samples, and CTAB followed by TCA solutions on another set of samples. Because HgCl(,2) did not rupture bacteria as did the CTAB/TCA treatment, these samples were used to determine, respectively, extracellular and total (extracellular plus intracellular) ammonia (NH(,3)) and free amino acids, and intracellular concentrations by differences. Samples of WRC were treated to allow determination of total NH(,3) and amino acid concentrations. Casein degradation was assessed by means of the alkali labile phosphorus, naturally bound to the casein, as a marker for undegraded casein in the rumen. ...