Treatment and supplementation of rice straw for ruminant feeding in Vietnam / Kjemisk behandling av rishalm og effekt av tilskudd til halmbaserte fôrrasjoner til drøvtyggere i Vietnam
Treatments using unslaked lime (3% or 6%) and/or urea (2% or 4%) for improved utilization of rice straw as ruminant feed were evaluated involving chemical analysis, in-sacco technique, in-vitro gas production test, intake determination, digestion and feeding trials. Wet brewers’ grains (WBG) and sugarcane molasses (SCM) as supplements to rice straw based diets, at 10% straw dry matter (DM), were also assessed in terms of their effects on rumen ecosystem efficiency as well as biological and economic responses in feeding trials. Results are reported in the form of four original research papers following a review one.
Treatment with urea highly increased the nitrogen (N) content of straw and significantly reduced its neutral detergent fibre (NDF) and hemicellulose, but not acid detergent fibre (ADF) and acid detergent lignin (ADL). Lime proved to be more powerful, significantly reducing not only NDF and hemicellulose, but also ADF and ADL. All the treatments were found to be effective in improving in-sacco degradability, in-vitro gas production, voluntary intake and apparent digestibility of rice straw. However, 2% urea alone seemed to be too low for effective treatment and 6% lime too high for rumen ecosystem and the animal. Treatments using 3% lime alone, 4% urea alone, or 3% lime plus urea (2% or 4%) effectively improved growth rate, feed utilization and economic efficacy in growing cattle. When lime and urea were combined for straw treatment their effects were somewhat additive, making the overall effects better than those obtained when either chemical was used alone. Nevertheless, in combination with lime, 4% urea showed little advantage over 2% urea, due probably to negative interactions. Among the treatments tried, 3% lime plus 2% urea was best biologically and economically justified.
Supplementation with 10% WBG or SCM remarkably improved growth rate, feed utilization and thus economic efficacy when young beef bulls were fed on straw based diets. WBG proved to be more effective than SCM. The first was synergistic to both untreated (US) and treated (TS) straws at the rumen level together with possible effects at post rumen level. The latter was only synergistic to US and seemed to exert effects simply at the rumen level.
