Pretreatment under mild conditions in the presence of water (solvolysis) or aqueous orthophosphoric acid (phosphorolysis) was used to increase the nutritional value of sugar cane bagasse for cattle feeding. The best pretreatment conditions were defined as those in which the highest in situ degradability rates (ruminal digestion) were achieved with the least energy consumption and/or production of inhibitory products. Heating sugar cane bagasse up to 197 degrees C (13.5 atm) at a 4:1 (w/w) water ratio was shown to be a compromised condition for solvolysis, as higher temperatures would require more energy consumption without adding too much to the already high 60% ruminal degradability of the residue in relation to its dry weight. These rates of degradability were shown to be further enhanced to almost 70% by adding 2.9% (w/w) orthophosphoric acid as an acid catalyst. A mathematical treatment of the kinetic data describing ruminal digestion of each of the pretreated residues was also developed in this study.