Effects of acidogenicity value of feedstuffs on rumen fermentation characteristics and nutrients digestibility

Abstract

The aims of the three studies in this thesis were to evaluate acidogenicity value (AV) of various feedstuffs, and to observe effects of dietary AV on rumen fermentation characteristics and nutrients digestibility. Acidogenicity value (AV) of feedstuffs was determined by the dissolution of Ca from CaCO3 powder added to the media on 24 h incubation. In experiment 1, initial pH varied across feedstuffs, ranged 3.75 to 6.76. Feedstuffs with high protein content had relatively high initial pH values compared with others. In addition, buffering capacity was relatively high in ash rich feeds, and relatively low in starch rich feeds. Protein feed sources had low AV and starchy feeds high AV. A relationship of AV between two different in vitro results indicated highly correlated (r=0.95). Acidogenicity value had negative relationship on pH (r=0.92), but positive relationship on gas production (r=0.71). In the following two experiments, three diets were formulated to be isoenergetic and iso-nitrogenous with different AV. In experiment 2, it appears that pH, NH3-N concentration and A:P ratio tended to decrease, but gas production, VFA production and DM disappearance tended to increase in high AV treatment compared with low or medium AV treatments In experiment 3, the rumen pH tended to decrease in order of high AV > medium AV > low AV treatment. While there were no significant effects of AV on NH3-N concentration, enzyme activity and nutrient digestibility. In addition, total VFA and individual VFA concentrations were no significant difference but tended to increase in high dietary AV treatment. Therefore, the studies have shown that the dietary AV was higher in concentrates in comparison to forage, and protein feed sources has lower AV compared with starch feed sources. In addition, the studies have indicated that effects of dietary AV on rumen fermentation and nutrients digestibility was little. However, it appears that high dietary AV had relatively more negative effect on rumen fermentation compared with low dietary AV treatments.