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Cell-Wall Fractions and In Vitro Digestibility of Peruvian Feedstuffs¹

North Carolina State University, Raleigh 27607 and and National Agrarian University, La Molina, Lima, Peru

Abstract

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.

¹ Paper No. 4303 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh. This research was supported by the North Carolina State University Agricultural Mission to Peru (USAID Contract), the Forages Program of the National Agrarian University, and the Peruvian Ministry of Agriculture.

² Formerly Research Assistant, Forages Program, National Agrarian University. Present Address: IVITA, Apartado 245, Pucallpa, Peru.