PRETREATMENT OF SUGAR-CANE BAGASSE FOR ENHANCED RUMINAL DIGESTION

Crop residues, such as sugar cane bagasse (SCB), have been largely use d for cattle feeding However, the close association that exists among the three major plant cell-wall components, cellulose, hemicellulose, and lignin, limits the efficiency by which ruminants can degrade these materials Previously, we have shown that pretreatment with 3% (w/w) p hosphoric acid, under relatively mild conditions, increased considerab ly the nutritional value of SCB. However, in this preliminary study, p retreated residues were not washed prior to in situ degradability assa ys because we wanted to explore the high initial solvability of low-mo l-wt substances that were produced during pretreatment We have now stu died the suitability of water- and/or alkali-washed residues to in sit u ruminal digestion. Alkali washing increased substrate cellulose cont ent by removing most of the lignin and other residual soluble substanc es As a result, the ruminal degradability of these cleaner materials h ad first-order rate constants five times higher than those substrates with higher lignin content (e.g., stem-exploded bagasse) However, alka li washing also increased the time of ruminal lag phase of the cellulo sic residue, probably because of hemicellulose and/or lignin removal a nd to the development of substrates with higher degree of crystallinit y. Therefore, longer lag phases appear to be related to low microbial adherence after extensive water and alkali extraction, as Novellas to the slower process of cellulase induction during ruminal growth. The k inetic data on ruminal digestion were shown to be very well adjusted b y a nonlinear model. Although pretreatment enhances substrate accessib ility, the occurrence of an exceedingly high amount of lignin byproduc ts within the pretreated material reduces considerably its potential d egradability.