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Steam Treatment of Crop Residues for Increased Ruminant Digestibility. I. Effects of Process Parameters^1,2,

US Department of Agriculture⁴, Berkeley, CA 94710

Abstract

Rice straw, sugar cane bagasse and sugar cane field trash were steam treated at pressures ranging from 7.0 to 42.2 kg/cm² with and without added chemicals. Aqueous NaOH, NH₃ and urea were additives used at levels of up to 4.5% of dry weight. Effect of processing parameters was measured by an enzymatic in vitro digestibility assay. The general effect of increased pressure and (or) treatment time on rice straw was to increase in vitro digestibility over that of untreated straw. There was some indication that a maximum digestibility may be reached and then followed by a decline upon further treatment. Highest digestibilities were reached at 21.1 kg/cm² both with and without additives. After 1.5 min at this pressure, rice straw digestibility improved to maximums of about 47%, without additives, and 64% with NaOH. Initial rice straw digestibility was 26%. Neither aqueous NH₃ nor urea increased digestibility of steam-treated material, but both increased nitrogen content of the product. However, less additive was retained as the amount used increased. Moisture content of treated material was typically between 40 and 50% after steam condensation and water entrainment. Depending on treatment time and pressure, 5 to 16% of the crop residue was volatilized and lost when the reactor was vented to the atmosphere.

¹ We thank the Masonite Corp. for loaning us its pressure vessel and Dr. Bruce Mackey, consulting statistician at this USDA Center, for statistical analysis of data.

² Reference to a company and (or) product is for purposes of information only and does not imply USDA approval or recommendation of the product to the exclusion of others which may also be suitable.

³ Deceased.

⁴ SEA, Western Regional Research Center, Berkeley, CA 94710.