The influence of anaerobic fungi on rumen volatile fatty acid concentrationsin vivo

Abstract

SummaryElimination of the rumen anaerobic fungi from sheep fed chemically-treated barley straw diets resulted in elevated proportions of propionic acid in rumen liquor (fromca. 0·15 to 0·30). Subsequent inoculation of these sheep with a pure culture of fungus decreased propionate concentrations within 3 days to the levels observed in control animals that possessed abundant fungal populations throughout the experiment.Confirmation that propionate itself was not responsible for the elimination of the fungi was provided by the results of a second experiment in which intraruminal infusions of propionic acid failed to reduce fungal growth or prevent recolonization in sheep previously rendered fungi-free.In a third experiment with sheep fed untreated barley straw, monensin supplementation produced the well known elevation of propionate concentrations. However, this treatment also resulted in the elimination of rumen anaerobic fungi from the animals. The magnitude of the increased concentration of rumen propionic acid, resulting from the elimination of the anaerobic fungal flora, indicates an important role for the fungi in the fermentation of high-fibre diets. In addition, these findings indicate that the well known elevation of propionate levels produced by monensin may likewise be effected directly by removal of the rumen anaerobic fungi.

Effects of 3 chemical treatments on in vitro fermentation of rice straw by mixed rumen microbes in the presence or absence of anaerobic rumen fungi

“…In addition, this limited suppressive effect of the antibiotic on rumen protozoa may have influenced the extent of degradation of plant material by the rumen microorganisms (fig 2b). Whereas the decrease in the degradation during incubation with B + P cannot be entirely attributed to fungal suppression, the addition of this antibiotic (cycloheximide) resulted in a fermentation pattern similar to that reported for other antifungal substances (Elliot et al, 1987;Cann et al, 1993a,b). The effect of cycloheximide inclusion resulting in lower digestibilities during the 48-h and 72-h incubations also throws light on the importance of rumen fungi during the later stages of fermentation when more refractory materials remain in the fermentation system.…”

“…The significantly low pH (table III and IV) during Sct fermentation was inconsistent with the results in vivo with sheep, where the ruminal pH of the animals being fed Sct was between 6.8 and 6.9 (Elliot et al, 1987;Cann et al, 1993b). This observation is explained by the buffering ability of the rumen ecosystem.…”

“…The significantly higher proportion of propionate resulting from Sct fermentation was shown to be due to the fungicidal effect of Sct (Cann ef al, 1993b;Elliot et al, 1987). The A:P ratio of less than 1 is rarely encountered during the fermentation of fibrous materials (Miron and Ben-Ghedalia, 1987;Cameron et al, 1991;Cann et al, 1991 The suppression of the anaerobic fungi leading to a higher propionate proportion at the expense of acetate proportion has been demonstrated by using other antifungal substances, namely polyoxin D (Cann et al, 1993a,b) and monensin (Elliot et al, 1987). The results of the present experiment, therefore, show that the suppression of rumen fungi may decrease the microbial degradation of fibrous materials and will surely shift the fermen-tation toward increased production of propionate while suppressing the acetate pathway.…”

“…L'objectif de cette étude était de comparer la dégradation et les produits de (1987) and Cann et al (1993b) observed that treatment with sodium chloride/acetic acid mixture (Sct) decreased lignin content but also drastically depressed intake by sheep. This reduced intake of Sct-chaffed barley straw has been attributed to the fungicidal effect of the treated straw (Elliot et al, 1987). However, it has been reported by Windham and Akin (1984) that suppressing fungal activity in vitro did not decrease dry matter degradation of ground alfalfa and coastal bermuda grass.…”

“…Rice straw (Rs) was treated chemically by 3 methods, namely, ammoniation at 3 g NH 3 /100 g DM (At) (Cann et al, 1991 ), alkaline hydrogen peroxide treatment (Athp) (Lewis et al, 1988) and sodium chlorite/acetic acid mixture treatment (Elliot et al, 1987). During Athp treatment, NH 4 0H was used as the alkali instead of NaOH.…”