Rumen-buffering capacity using dietary sources and in vitro gas fermentation

Abstract

The present study aimed to compare the effect of the rumen-buffering capacity of dietary sources and urea supplementation on ruminal kinetic gas production, rumen pH and fermentation efficiency and degradability, using in vitro gas-production techniques. The treatments were arranged according to a 4 × 3 factorial arrangement in a completely randomised design. The first factor was a rumen-buffering source, including the following: no buffering, and supplementation of 2% of sodium bicarbonate (NaHCO3), 2% of banana flower powder I (BAFLOP-I; Musa (AAA group)) or 2% of BAFLOP-II (Musa sapientum L.) in total substrate. The second factor was urea supplementation at 0, 3% or 6% of total substrate, as a non-protein nitrogen source. Dietary substrate was provided by roughage–concentrate fed at a ratio of 30 : 70 and two rumen-fistulated dairy steers were used as rumen-fluid donors. The chemical compositions and mineral element contents of both BAFLOP-I and BAFLOP-II were similar. The pH declined below 6.0 as a result of using a high concentrate ratio; however, inclusion of buffering sources increased the pH, which led to an improvement of efficiency of rumen fermentation, microbial protein synthesis, microbial growth and nutrient digestibility. The intercept values for the different treatments representing gas production from soluble fractions, gas production from the insoluble fraction, gas production rate, potential extent of gas production and cumulative gas production (120 h of incubation) were significantly different between no buffering and buffering groups (P < 0.05) and increased with an increasing level of urea supplementation. Moreover, in vitro true and neutral detergent fibre digestibility as well as the number of ruminal microorganisms by direct counts (protozoa, fungi and bacteria) were higher with supplementation of buffering sources and increased linearly with an increasing supplementation level of urea. However, under the present study, there were no differences among the effects of the three buffering agents (NaHCO3, BAFLOP-I and BAFLOP-II) on ruminal kinetic gas production, rumen pH and fermentation efficiency, and digestibility (P > 0.05). In addition, the concentration of ruminal ammonia-nitrogen increased with an increasing level of urea supplementation. On the basis of the present experiment, it can be concluded that supplementation of BAFLOP either with or without urea as non-protein nitrogen could enhance rumen ecology and digestibility. The present study suggested that either BAFLOP-I or BAFLOP-II could be used as a dietary rumen-buffering agent supplemented at 2%, together with urea at up to 6% of total diet substrate, when animals are fed a diet of roughage–concentrate at an ratio of 30 : 70, with rice straw as the main roughage source.