Importance of Phosphorus Supplementation in Improving Fermentability, Microbial Protein Synthesis and Degradability of Ammoniated Rice Straw

Abstract

Rumen microbes need minerals for supporting its growth and activity in fermenting and digesting feeds. However, the supply of minerals should match the amount of energy that is available for microbial growth and protein synthesis, and for fermentation. An experiment is carried out to study the importance of phosphorous (P) supplementation in rations containing ammoniated rice straw (RS) and concentrate on its fermentability, microbial protein synthesis and degradability. The in vitro experiment was carried out following the first stage of Tilley and Terry method. The treatments consisting of four diets were A = 50% ammoniated rice straw (RS) + 50% concentrate (control), B = A + P supplement at 0.2%, C = A + P supplement at 0.4%, and D = A + P supplement at 0.6%. Completely randomized design was used as the experimental design with differences among treatment means were examined using Duncan multiple range test. Variables measured were ammonia (NH3) and volatile fatty acid (VFA) concentrations, total bacterial and cellulolytic bacterial population, cellulolytic enzyme activity, as fermentability indicators and microbial protein synthesis, as well as degradability indicators including dry matter (DM), organic matter (OM), neutral detergent fibre (NDF), acid detergent fibre (ADF) and cellulose. The results indicate that P supplementation at the levels of 0.2, 0.4 and 0.6% reduced ammonia concentration (P<0.05) and increased VFA concentration (P<0.05), but did not affect other variables. Degradabilities of DM, OM, NDF, ADF and cellulose were increased by P supplementation (P< 0.05). It is concluded that P supplementation is important for improving fermentability and degradability of rations containing ammoniated RS and concentrate. The improvement occurred through the increase in cellulolytic bacterial population, cellulolytic enzyme activity, total VFA concentration, and degradabilities of DM, OM, and fibrous fraction. The best level of P supplementation is 0.4% (DM basis).