Ruminal escape and apparent degradation of amino acids administered intraruminally in mixtures to cows.
The apparent ruminal degradation and escape of amino acids (AA) administered in 9 different mixtures of essential AA and 8 different mixtures of nonessential AA were studied using two cows fitted with ruminal cannulas. The 600-mmol AA mixtures, which were administered intraruminally using polyethylene glycol as a liquid marker, contained equal amounts of two, four, or eight AA. The amounts of each of the AA in the mixtures were 300, 150, and 75 mmol, respectively. Ruminal degradation and escape were compared with values previously reported for AA administered individually. Across doses, the mean rate of initial degradation (degradation during the 1st h after administration) of essential AA was 26% when the AA were administered in mixtures and 45% when the AA were administered individually. For nonessential AA, the corresponding values were 34 and 54%. Across doses, mean ruminal escape during the first 8 h after essential AA administration was 22% when the AA were administered in mixtures and 16% when the AA were administered individually. For nonessential AA, the corresponding values were 13 and 11%. After intraruminal administration of AA, both individually and in mixtures, significant negative correlations were found between rates of degradation during the 1st h and ruminal escape during an 8-h period. Some AA mixtures caused a net increase in the concentration of other AA in ruminal fluid 1 h after administration. Twelve of the mixtures that did not contain Ala caused a considerable net increase in the concentration of this AA, and 3 AA mixtures containing Arg and Ala caused a marked net increase in the concentration of Trp.
Degradation of methionine by rumen contents in vitro and efficiency of its protection
Abstract Degradation of methionine (M), soya isolate (S) and casein hydrolysate (C) has been evaluated by incubation of these substrates (100 mg) with sheep rumen contents in vitro, in the presence of starch (250 mg). Five incubations were performed using one adult rumen fistulated sheep fed 300 g of hay and 300 g of concentrate daily. Total NH3 production at different sampling times (after 2, 4, 6, 8 and 24 h of incubation) was calculated by subtracting the net NH3-N production observed in the incubation containing starch only from that produced in the incubation containing the substrate. Protected M preparations, Smartamine (Sm) and Mepron (Mp), were also used. During two incubations of M, using four sheep on permanent pasture or fed four different hays, it was shown that the net disappearance of free M matches net NH3 production at both low (2 mM) and high (20 mM) M concentration. The results indicate that the initial M degradation rate (3 h of incubation) was 12–14% that of C and never exceeded 1.5 mmol h−1 l−1 of rumen contents. Adaptation of the sheep rumen by daily introduction of 5 or 20 g of DL-methionine for 21 and 8 days, respectively, did not change this result (three to four incubations with rumen contents of three sheep fed 300 g of hay and 300 g of two different concentrates). The results also indicate that protection against rumen degradation was effective for Sm but not for Mp. The ‘effective degradation rate’ of M was estimated as 0.30 that of protein. Considering the high price of protected M (four to five fold the price of non protected M), and the low degradation rate of M, it is suggested that the latter be used at 1.43 of the amount normally added as rumen protected M, to obtain the same result.
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.