Cell-Wall Fractions and In Vitro Digestibility of Peruvian Feedstuffs1

Forty-four feedstuffs from the temperate, subtropical and tropical regions of Peru were analyzed for in vitro true dry matter digestibility (IVTDMD), crude protein, and cell-wall constituents. Included were cultivated and native grasses and legumes, crop residues, and other materials. Among the cultivated forage species there were noticeable differences in maturity effects on IVTDMD and concentration of cell-wall fractions; maturity and species effects were not necessarily related to “tropical” or “temperate” species type. The results were used to test species differences in the relationship between chemical fractions and IVTDMD by the use of linear regression analysis. The model which consistently gave highest R2 values when applied to various data subgroups and individual forage species is represented by the equation IVTDMD = 117.2 − .59 ± .05 HC − .76 ± .09 C − 1.93 ± .18 L where HC = hemicellulose, C = cellulose and L = permanganate lignin; this equation being derived from a fit of all observations (n = 354) and giving an R2 value of .64. The same model applied to the subgroupings of grasses, legumes and fibrous crop residues yielded R2 values of .54, .78 and .69, respectively. A prediction based only on the total cell-wall fractions gave results slightly inferior to the model which included HC, C and L separately.