An in vitro cultured rumen inoculum improves nitrogen digestion in mulga-fed sheep

Abstract

Mixed cultures of anaerobic micro-organisms were derived from feral goat rumen fluid (FGRF) using a laboratory fermentor to selectively culture microbes actively degrading mulga, and were evaluated as rumen inocula in digestion and liveweight studies with mulga-fed sheep. When placed in the rumen of sheep, FGRF enhances mulga digestion; however, limited supplies of feral goats, the labour involved in locating and mustering goats, and likely variations in the microbial composition of FGRF between animals and localities make the production of an in vitro cultured inoculum a desirable alternative to enable widespread adoption. The cultured inoculum significantly (P < 0·05) improved nitrogen digestion and retention in mulga-fed sheep by 16 and 76%, respectively. Inocula consisting of simplified mixtures of bacteria isolated from sheep, feral goats, and native marsupials did not affect mulga digestion. In the first of 2 liveweight studies, sheep inoculated with the fermentor inoculum lost significantly less weight than uninoculated sheep for the first 57 days (0·3 v. 4·6 kg); however, after 83 days the difference in the rate of liveweight loss between the fermentor inoculum group and the uninoculated sheep was not significant (53 v. 95 g/day). In the second study, liveweight loss was not significantly reduced by the fermentor inoculum. An inoculum based on FGRF, and produced in vitro using a fermentor, is potentially valuable to grazing enterprises reliant on mulga-fed sheep. However, problems in generating a consistent inoculum need to be addressed before such an inoculum can be generally considered.