In vitro digestibility of forages as influenced by source of inoculum (sheep rumen versus Rusitec fermenters) and diet of the donor sheep

Abstract

An eight vessel Rusitec unit and four rumen fistulated sheep were used to determine if sheep rumen liquor in the true in vitro digestibility technique of Van Soest et al. [Proceedings of the 10th International Grasslands Congress. Helsinki, 1966, p. 438] could be replaced with Rusitec fluid. Two diets differing in their forage:concentrate ratio (80:20 (C20) and 20:80 (C80), g/100 g fresh matter) were fed to four donor sheep and four Rusitec vessels, so that each treatment was conducted in quadruplicate. Samples of fifteen forages (i.e. 12 hays, two cereal straws and a sample of Erica arborea) were incubated with sheep rumen liquor and with Rusitec fluid for 48 h followed by 1 h of extraction with boiling neutral detergent solution to determine their in vitro dry matter digestibility (DMD). The use of rumen liquor from sheep fed diet C80 resulted in lower ( P<0.05) in vitro DMD for six forages (oat straw and five hays) compared to rumen liquor from sheep fed diet C20. In contrast, there was no effect ( P>0.05) of the diet fed to the Rusitec system on the in vitro DMD of forages, with the exception of one hay which showed a lower digestibility ( P<0.05) when it was incubated with Rusitec fluid from C80-fed vessels. Rusitec fluid resulted in lower ( P<0.05) in vitro DMD than sheep rumen liquor for all forages tested, with the exception of Erica arborea with diet C80. The in vivo DMD of the 12 hays was accurately predicted by both rumen sheep liquor and Rusitec fluid, and values of the coefficient of determination (mean values of 0.885 and 0.877 for sheep rumen liquor and Rusitec fluid, respectively) and the R.S.D. (mean values of 2.199 and 2.279) were similar to those obtained previously for the same 12 hays with the technique of Tilley and Terry [J. Br. Grassl. Soc. 18 (1963) 104] and the pepsin–cellulase method of Jones and Hayward [J. Sci. Food Agric. 24 (1973) 1419]. Rusitec fluid can be used as a source of micro-organisms for determining true in vitro digestibility of forages.