CONSUMPTION OF DIGESTIBLE ENERGY BY SHEEP AS PREDICTED FROM THE CONCENTRATION OF IN VITRO DIGESTIBLE ENERGY, CELL-WALL CONSTITUENTS, AND CRUDE FIBER IN COARSE ROUGHAGE

Abstract

Six forage species were harvested at four to seven maturity stages annually for four years to provide 102 lots of hay. Each lot was fed to four sheep in the year after harvest to determine the voluntary consumption of digestible energy (kcal daily/kg0.75 of body weight). Samples of each hay were assayed for in vitro digestible energy, cell-wall constituents, and crude fiber. The consumption of digestible energy was correlated (P < 0.01) with each of the three assay measures within each species of hay. The regressions were generally linear (P < 0.05), and were similar in homogeneity of variance, and slope and elevation or regression between two alfalfa cultivars, and between the four grass species. Pooled regressions for the alfalfas and for the grasses differed (P < 0.05) only in elevation of regression. This was caused by a greater consumption of alfalfa hay than of grass hay at similar concentrations of digestible energy and cell-wall fiber. The in vitro digestible energy assay was superior to either of the fiber assays for the prediction of consumption of digestible energy for the grass hays, the coefficients of variation from regression (CV) being 18% for the in vitro assay and 24% for each fiber assay. Neither of the fiber measures affected the CV when included as secondary independent variables in a multiple regression. In the alfalfa hays the three assays each had a CV of 16%. The CV was reduced to 15 and 12%, respectively, when cell-wall constituents or crude fiber were included as a secondary independent variable. The accuracy of the laboratory assay was comparable with that of animal feeding experiments, in which the CV of feed consumption has been reported as 16 to 18% between sheep and 10 to 12% between cattle.