Abstract
Environmental pressures of ruminant production could be reduced by improving digestive efficiency. Previous in vivo attempts to manipulate the rumen microbial community have largely been unsuccessful probably due to the influencing effect of the host. Using an in vitro consecutive batch culture technique, the aim of this study was to determine whether manipulation was possible once the bacterial community was uncoupled from the host. Two cross inoculation experiments were performed. Rumen fluid was collected at time of slaughter from 11 Holstein-Friesian steers from the same herd for Experiment 1, and in Experiment 2 were collected from 11 Charolais cross steers sired by the same bull and raised on a forage only diet on the same farm from birth. The two fluids that differed most in their in vitro dry matter disappearance (IVDMD; “Good,” “Bad”) were selected for their respective experiment. The fluids were also mixed (1:1, “Mix”) and used to inoculate the model. In Experiment 1, the mixed rumen fluid resulted in an IVDMD midway between that of the two rumen fluids from which it was made for the first 24 h batch culture (34, 29, 20 g per 100 g DM for the Good, Mix, and Bad, respectively, P < 0.001) which was reflected in fermentation parameters recorded. No effect of cross inoculation was seen for Experiment 2, where the Mix performed most similarly to the Bad. In both experiments, IVDMD increased with consecutive culturing as the microbial population adapted to the in vitro conditions and differences between the fluids were lost. The improved performance with each consecutive batch culture was associated with reduced bacterial diversity. Increases in the genus Pseudobutyrivibrio were identified, which may be, at least in part, responsible for the improved digestive efficiency observed, whilst Prevotella declined by 50% over the study period. It is likely that along with host factors, there are individual factors within each community that prevent other microbes from establishing. Whilst we were unable to manipulate the bacterial community, uncoupling the microbiota from the host resulted in changes in the community, becoming less diverse with time, likely due to environmental heterogeneity, and more efficient at digesting DM.
Highlights
With increasing demand for milk and meat there comes a need to increase the productivity of current livestock systems whilst minimizing their environmental impact
Over the following 2-week period (CBC2-CBC8), in vitro dry matter disappearance (IVDMD) of all three rumen inoculums increased with each consecutive batch culture (CBC) until the end of day 9 (CBC5), after which point, maximum IVDMD was reached (Figure 1B)
From the first 24 h fermentation (CBC1) to the last (CBC9), each inoculum improved its ability to digest dry matter, with average IVDMD increasing by 74% (27.4 ± 7.02 g per 100 g DM for CBC1, increasing to 47.9 ± 0.70 g per 100 g DM for CBC9)
Summary
With increasing demand for milk and meat there comes a need to increase the productivity of current livestock systems whilst minimizing their environmental impact. Rumen microbial profiles from animals with low residual feed intake (i.e. more efficient animals) have been shown to cluster together, and away from animals with a high residual feed intake suggesting a particular microbiota may be responsible for more efficient digestion (Guan et al, 2008; Carberry et al, 2012). Previous in vivo attempts to manipulate the microbial community in this way have determined that host factors have a strong influence on ruminal processes by a mechanism(s) that does not appear to correlate, at least strongly, with particular microbiota In studies by both Weimer et al (2010) and Zhou et al (2018) where near total exchange of rumen content (>95%) was performed between animals, the microbial population was shown to revert to that of the original host animal. Both studies demonstrated inter-animal variation in the ability of the host-specific microbiota to re-establish itself suggesting host factors as a determinant
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