The energy values and nutritive value indices of Digitaria decumbens, Sorghum almum, and Phaseolus atropurpureus

Abstract

Two subtropical grasses, Digitaria decumbens and Sorghum almum, and one legume, Phaseolus atropurpureus (var. Siratro), cut at different ages were fed to sheep indoors to measure voluntary intake and apparent energy digestibility. Energy values of dry matter ranged from 4.11 to 4.48 kcal/g and those of organic matter from 4.47 to 4.94 kcal/g. There was a positive correlation between the energy value of organic matter and the crude protein content (r = 0.84, P < 0.01). The apparent digestibility of feed energy was correlated with species, age, and dry matter digestibility but there were significant differences between the regression equations for each species. Age was the most important factor determining the digestible energy content of the three species, and the energy value of digestible organic matter varied from 3.860 to 4.801 kcal/g. This value was positively correlated with protein content.

The intake of digestible energy (kcal/kg^0.75) was approximately four times as great for young cuts as for mature cuts of both grasses. Nutritive value index (N.V.I.) was closely correlated with the intake of digested energy for the three species (r > 0.998, P < 0.001), but the regression coefficient for S. almum was significantly different from those for D. decumbens and P. atropurpureus. The relative merits of the digestible energy and N.V.I. methods of expressing the energy value of pasture are discussed, and it is concluded that digestible energy is the more suitable method.