Journal of Dairy Science 84 (2001)suppl. 1. - ISSN 0022-0302 - p. 286 - 286.
ID Lelystad, Institute for Animal Science and Health
Refereed Article in a scientific journal
Three experiments were conducted to evaluate effects of pH,substrate and ammonia levels on starch degradation (STAD) and on gas production to look into the optimal conditions for GP technique in starchy feedstuff evaluation. The pH effect on STAD of six starchy samples was studied by using phosphate buffer mixed with rumen liquor in 24-h in-vitro incubation. The results indicated p H5 adversely affected STAD and no significant differences were found among p H7, 6and 5.5, even though STAD appeared larger at p H6. The ranking in STAD degree of the starchy feedstuffs was found in vitro degradation with rumen fluid at all p Hlevels. Barley, wheat and tapioca showed the highest STAD and potato starch and maize the lowest in STAD at each pH level. Minimum STAD took place in first 4-h incubation. Sub-strate level did not affected total GP (g-1OM), but influenced total GPper incubated bottle. On the other hand, substrate concentration significantly affected the shape of gas curve. Increased substrate reduced the time to reach the half-maximal gas production and curve sharpness.Thus substrate concentration affected the fermentation rate, and higher increased substrate concentration increased GP rate in the OM range of 100 500mg substrate. Ammonia carbonate concentration (ACC) did not affected total GP (g-1OM) in such starchy feedstuffs, but it affected the shape of GP profile. GP rate was improved with the increase of ammonia carbonate in the buffer. GP rate of 0.0 ACC was significantly slow from those of other ACC. Though GP rate of 1.0 ACC was the fastest, but no significant differences were found among ACC levels of1.0, 1.5 and 2.0 in GP rate. The finding from this study proved p H6.9,1.0g ACC and 400mg substrate in buffered rumen fluid, the condition of media was currently used in ID-Lelystad, were appropriate in GP technique for the STAD evaluation of starchy sample. These experiments emphasize the need for standardization of GP technique to facilitate the comparison of results among the samples and laboratories. This need will be extreme when GP is used for feed evaluation. The sensitivenessin GP rate and extent among starchy samples imply the great potential and accuracy of GP technique in evaluating the characteristics of different starchy feedstuffs.
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