True Digestibility and Estimation of Nutritive Value in Sorghum Silage

Abstract

The nutritive uniformity of Lucas test and true digestibility of chemical components were investigated for 21 silages prepared from 19 varieties of sorghum and sudangrass. The varieties tested were characterized of the types of grain, dual purpose, sorgo, sudangrass or sorghum-sudangrass hybrid by the utilization and plant type and also of the types of normal, sugary or higher digestibility by nutritional property. Apparent digestibilities of the organic cellular contents (OCC), organic cell wall fraction hydrolyzed by cellulase (Oa) and nitrogen cell wall free extract (NCWFE) were higher than that of residual organic cell wall after cellulase digestion (Ob). Endogenous excretion and true digestibility of the fraction of OCC plus Oa were estimated about 15% and 100%, respectively. Digestibilities of the Ob fraction in bmr-18 homozygotes were higher than those of the other silages. The nutritive uniformity of the Ob fraction was much lower than those of the other chemical component. However, the nutritive uniformity of the Ob fraction of the silages became much higher, as the bmr-18 and bmr-6 homozygotes and sudangrass were eliminated. The digestibility of the Ob fraction tended to be depressed by increasing cellular contents (CC) in the silages. An exponential model for the content of digestible Ob (DOb), as based on the relationship between the digestibility of the Ob fraction and CC, was proposed as follows: DOb=α・e^<β・Ob> where, α and β were constants, and β explained true digestibility curve of Ob. Therefore, we derived a following function for estimating TDN. TDN=OCC+Oa+DOb+bias. Values of α, β and bias were estimated 3.53, 0.0309 and -9.64 in normal varieties (SE=2.1), and 5.34, 0.0334 and -8.83 in bmr-18 homozygotes (SE=2.1), respectively.