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Abstract

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

Abstract

Mixed cultures of anaerobic microorganisms from feral goat rumen fluid (FGRF) were maintained in a laboratory fermentor to selectively culture microbes actively degrading mulga (Acacia aneura), and then evaluated as rumen inocula in digestion and liveweight studies using mulga-fed sheep. Sheep rumen fluid (SRF) inoculum was obtained from 3 donor sheep that had been inoculated with FGRF. Three mixtures of bacteria (from rumen contents of sheep and feral goats, fermentor inoculum and intestines of marsupials) containing Selenomonas strain JJP014B and Actinomyces strains JJP018 and JJP030 (A), JJP014B, JJP018 and Streptococcus strain JJP055 (B), and JJP030 and JJP055 (C), were prepared. In the first digestion study, 20 Merino sheep, 3-4 years old, were individually penned and fed ad libitum on mulga leaves. Sheep were assigned to 4 groups and inoculated with FGRF, SRF, fermentor inoculum, or left uninoculated. In a second digestion study, another group of 20 sheep was divided into 4 groups and inoculated with bacterial mixes A, B, C or left uninoculated. Nitrogen balance studies commenced 40 days after inoculation in the first study and 21 days after inoculation in the second study. In the first 12-week liveweight study, 30 sheep, 3-4 years old, allocated to 3 groups of 10 each on the basis of weight, were inoculated with bacterial mix A or fermentor inoculum, or left uninoculated. In a second 12-week liveweight study, 36 sheep were allocated to 6 groups on the basis of their weights, and in a 2 × 3 × 6 factorial design, 3 groups were inoculated with fermentor inoculum while 3 groups remained uninoculated. In all treatments 200 ml of the assigned inoculum was given as an oral drench to the rumen via a stomach tube. Condensed tannin concentrations in mulga used in all studies are given. The cultured inoculum improved (P<0.05) N digestion and retention in mulga-fed sheep by 16 and 76%, respectively. DM intake and digestibility, and liveweight gain were not affected by fermentor inoculum. Inocula consisting of bacterial mixtures did not affect mulga digestion. In the first of the 2 liveweight studies, sheep inoculated with fermentor inoculum lost less (P=0.05) weight than uninoculated sheep and sheep inoculated with bacterial mix A for the first 57 days (0.3 vs. 4.6 and 3.4 kg); however, after 83 days there were no differences in the rate of liveweight loss for each group. In the second study, neither DM intake nor liveweight gain differed between the fermentor inoculum and uninoculated groups. The results suggest that an inoculum based on FGRF, and produced in vitro using a fermentor, is capable of improving digestion of mulga by sheep.