EFFECT OF MONENSIN ON PRODUCTION OF VOLATILE FATTY ACIDS FROM CELLULOSE , HEMICELLULOSES , PECTIN AND STARCH IN MIXED CULTURES OF RUMEN MICROORGANISMS

Simunek J., O. G. Savka, G. I. Kalacnjuk, S. B. Chon, M. Marounek: Effect of Monensin on Production of Volatile Fatty Acidsfrom Cellulose, Hemicelluloses, Pectin and Starch in Mixed Cultures of Rumen Microorganisms. Acta vet. Brno, 58, 1989: 215-223. In in vitro experiments we studied the effect of monensin on production of volatile fatty acids (VFA) from cellulose, hemicelluloses, pectin and starch in mixed cultures of rumen microorganisms. The following results were obtained: 1. Monensin lowered the concentration of VF A in cultures with cellulose. There were only minor differences in total VF A concentration between monensin-free and monensin-treated cultures with hemicelluloses, pectin and starch. 2. Monensin decreased the molar ratio acetate to propionate in cultures with hemicelluloses, pectin and starch, but increased this ratio in cultures with cellulose. 3. There were no significant differences between monensin from Elanco and its Czechoslovak analogue. Monensin maintained its effect throughout the 3-month experimental period. In vitro, rumen fluid, acetate, propionate, butyrate Monensin, an ionophore antibiotic, is widely used to improve the feed efficiency and stimulate the body mass gains of ruminants. While considerable research has been reported on how rumen fermentation is affected by monensin, information is limited on how this polyether ionophore affects the fermentation of particular components of plant cell material. Some experiments in vivo and in vitro have shown that monensin decreases the digestibility of fibre and fibrous components (Poos et al. 1979; Henderson et al. 1981; Wallace et al. 1981; Whetstone et al. 1981). Also salinomycin, an ionophore similar to monensin, has been shown to depress the digestibility of fibre (Zinn 1986). However, other authors found only minor

In in vitro experiments we studied the effect of monensin on production of volatile fatty acids (VFA) from cellulose, hemicelluloses, pectin and starch in mixed cultures of rumen microorganisms.The following results were obtained: 1. Monensin lowered the concentration of VF A in cultures with cellulose.There were only minor differences in total VF A concentration between monensin-free and monensin-treated cultures with hemicelluloses, pectin and starch.
2. Monensin decreased the molar ratio acetate to propionate in cultures with hemicelluloses, pectin and starch, but increased this ratio in cultures with cellulose.
3. There were no significant differences between monensin from Elanco and its Czechoslovak analogue.Monensin maintained its effect throughout the 3-month experimental period.

In vitro, rumen fluid, acetate, propionate, butyrate
Monensin, an ionophore antibiotic, is widely used to improve the feed efficiency and stimulate the body mass gains of ruminants.While considerable research has been reported on how rumen fermentation is affected by monensin, information is limited on how this polyether ionophore affects the fermentation of particular components of plant cell material.Some experiments in vivo and in vitro have shown that monensin decreases the digestibility of fibre and fibrous components (Poos et al. 1979;Henderson et al. 1981;Wallace et al. 1981;Whetstone et al. 1981).Also salinomycin, an ionophore similar to monensin, has been shown to depress the digestibility of fibre (Zinn 1986).However, other authors found only minor effect of ionophores on extent of digestion of cellulose (Dinius et al. 1976;Beever et al. 1987), hemicellulose (Dinius et al. 1976), fibre (Faulkner et al. 1985;Kobayashi et al. 1986; Lebzien et al. 1986) and starch (Whetstone et al. 1981;Zinn 1987).Nothing is known about the effect of monensin on digestion of pectin.
In this study we determined the effect of monensin on production of volatile fatty acids (VF A) from four principal plant polysaccharides in experiments in vitro.
We were particularly interested in the effect of monensin on the molar ratio acetate: : propionate in VF A formed during substrate decomposition, as it is known that the decreased molar ratio of acetate to propionate is the most consistent observation upon the monensin action in the rumen.We also compared monensin from Blanco Products Co. (USA) with the Czechoslovak analogue supplied by SPOF A and ascertained the effect of two months adaptation of inocula donors to monensin.

Inocula
Two fistulated wethers served as a source of rumen contents.The wethers were fed on a commercial concentrate (0.5 kg) and meadow hay ad libitum.The animals were fed twice a day.Samples of rumen contents were taken two hours after the morning feed (average pH = 6.56).In experiments with starch rumen fluid was used instead of rumen contents.Rumen fluid was prepared from whole rumen contents by straining through two layers of cheese cloth.
There are reports on the adaptation of rumen microorganisms to ionophores (de Jong and Berschauer 1983; Mackie et al. 1984).The same wethers were therefore adapted to 60 mg of monensin SPOF A I day for two months.

Incubations
Incubations were carried out in 300 ml serum bottles, closed by rubber bungs with ports for gas entry and exit and for sampling.Whole rumen contents or rumen fluid (50 ml) were diluted with McDougall buffer (l00 ml), which contained sources of nitrogen (total 0.45 g Nil), vitamins and trace elements.To provide the anaerobiosis, we used an addition of amorphous FeS into the medium and 02-free C02 atmosphere.The incubation time and amount of substrates was chosen with respect to the different rates of breakdown of particular carbohydrates (Marounek et al. 1985).Cultures were incubated without pH control.The pH fell from 7.0-7.2 to about 5.7 (starch) or 6.2-6.6 (other polysaccharides).Each experimental arrangement was incubated in four replicates.
Maize starch came from Czechoslovak Starch Works.The other chemicals were supplied by Lachema, Brno.
Analyses .The pH of the incubation medium was measured at the beginning and end of an incubation.Total VFA were determined by titration, after steam distillation.Their molar composition was determined by gas chromatography on a column of the N -A W Chromaton with 10 % SP 1200 and 1 % H3P04; length 1.8 m.The separation was carried out at 130° C with nitrogen (150 kPa) as carrier gas.

Results
Our results are summarized in Figs.1,2, 3 and 4. Fig. 1 shows the effect of monensin on VF A concentration in cultures with cellulose as energy and carbon sources.The VF A concentration was lowered in these cultures by monensin, no matter whether the inoculum was taken from adapted or non-adapted wethers.On the other hand, there were only minor differences in total VF A concentration between monensin-free and monensin-treated cultures with hemicelluloses (Fig. 2), pectin (Fig. 3) and starch (Fig. 4).
There were no significant differences between monensin from Elanco and its Czechoslovak analogue in our experiments.

Discussion
It follows from our results that there are substantial differences between cellulose and other polysaccharides as far as monensin-induced metabolic shifts during fermentation are concerned.Our results support opinion of those authors who found that monensin depressed the fermentation of fiber and cellulose.The depression of fiber digestion can be reasonably explained by the inhibitory effect of monensin on rumen cellulolytic bacteria, mainly ruminococci and butyrivibria (Dennis et al. 1981;Henderson et al. 1981).As it is known that monensin increases the productive efficiency of ruminants on both high-concentrate (review Galyean and Owens 1988) and roughage diets (Potter et al. 1976;Faulkner et al. 1985), we must assume that unfavourable effect of monensin on digestion of cellulose is compensated for by its benefitial effect on digestion of other components of plant matter and/or by increased post-ruminal cellulose digestion.
Monensin-induced metabolic shifts were basically the same in cultures from non--adapted and adapted (2 months) animals.Latter contained higher proportion of propionate and lower acetate.

Fig. 2 .
Fig. 2. Effects of monensin on VF A concentration and molar ratio acetate to propionate in 8 h-cultures with rumen contents and hemicelluloses (3g/150 ml).A = non -adapted wethers, B = adapted wethers, a = acetate, b = butyrate, p = propionate.Arrows indicate the VFA level at the beginning of the incubation.*, ** -Total VFA values are significantly different from those of monensin -free control at P < 0.025 and P < 0.005, resp.

~Fig. 3 .
Fig. 3. Effect of monensin on VFA concentration and molar ratio acetate to propionate in 6 h-cuItures with rumen contents and pectin (2g/150 ml).A = non -adapted wethers, B = adapted wethers, a = acetate, p = propionate, b = butyrate.Arrows indicate the VF A level at the beginning of the incubation.*, ** -Total VFA values are significantly different from those of monensin -free control at P < 0.05 and P < 0.005, resp. Fig,3

Fig. 4 .
Fig. 4. Effect of monensin on VF A concentration and molar ratio acetate to propionate in 8 h-cultures with rumen fluid and starch (3 gj150 ml).A = non -adapted wethers, B = adapted wethers, a = acetate, p = propionate, b = butyrate.Arrows indicate the VFA level at the beginning of the incubation.*, ** -Total VFA values are significantly different from those of monensin -free control at P < 0.05 and P < 0.001, resp.