The effect of polyethylene glycol (PEG 8000) supplementation on in vitro gas production kinetics of leaves from tannin containing trees

Abstract

The objective of this study was to determine the effect of inclusion of polyethylene glycol (PEG 8000) during in vitro incubation on gas production kinetics, organic matter digestibility (OMD) and the metabolisable energy (ME) content of foliage from the tannin containing tree species, Pistica lentiscus, Arbutus andrachne and Juniperus communis. The amount of gas produced when the foliage was incubated with buffered rumen fluid, was determined after 0, 3, 6, 12, 24, 48, 72 and 96 h of incubation in the presence of PEG at inclusions rates of 15, 30, 60 and 90 mg and in the absence of PEG. Their kinetics were described using the equation p = a + b (1-e -ct ). Addition of PEG resulted in an increased gas production at almost all incubation times in all tree species. However species showed variable responses. After 3 h of incubation the PEG addition showed no significant effect on gas production when the foliage from A. andrachne was incubated, but had a significant effect on gas production as duration of incubation extended. The increase in gas production in response to increased levels of PEG inclusion was linear for P. lentiscus and J. communis. However, when the PEG inclusion rates exceeded 60 mg there was no significant increase in gas production when A. andrachne was incubated. The estimated parameters such as gas production rate(c) and gas production (a) from the immediately soluble fraction were not affected by the level PEG treatment, except that PEG addition at 90 mg had a significant effect on the gas production (a) from immediately soluble fraction of leaves of J. communis. Gas production (b) from the insoluble fraction (mL) and potential gas production (a+b), OMD and ME of tree leaves increased significantly with increasing levels of PEG addition. However, when PEG inclusion exceeded 60 mg these parameters showed no significant increase when leaves from A. andrachne were incubated. Although the mean increase in OMD per mg PEG supplementation was 0.131 digestibility units, the increase in ME per mg PEG supplementation was 0.0201 ME units. The elevated levels of gas produced, and increased OMD and ME estimates with the inclusion of PEG demonstrated the negative effect of tannins in foliage on digestibility.

<i>In vitro</i> ruminal fermentation of leaves from three tree forages in response to incremental levels of polyethylene glycol

“…This may be due to the differences in CP concentrations ( Table 1) as response to PEG treatment is dependent on the level of protein in the substrates. Also, PEG binding to tannins can vary across forage species owing to the different chemical structure and molecular weight of tannins [3,5]. There was no difference in gas production from the insoluble fraction (b) upon PEG addition for all of the tree species in this study ( Table 2).…”

“…This is supported by [5] in a study utilizing (PEG 8000) to evaluate its effect on in vitro gas production kinetics of tannin containing tree leaves. There was no difference (P < 0.05) in potential gas production (a + b) in the leaves of G sepium and L. leucocephala when PEG was added ( Table 2).…”

“…Cumulative gas production after 48 hours of incubation increased with the level of PEG treatment with the response tending to curvilinear as the maximum effect is approached. The increase in cumulative gas production in response to PEG inclusion is supported by [3,5,10,[16][17][18]. Further increases beyond 200 mg PEG/g leaf substrate did not result in significant increases in cumulative gas production.…”

“…Recommendations on inclusion rates of PEG for complete tannin neutralization vary widely. According to [3], PEG supplementation levels of 1 g PEG per gram of sample for in vitro studies while, [5] indicated that 15 mg PEG would be sufficient to neutralize 75 g CT/g sample in the diets of animals. It was suggested by [7] that 2 g of PEG to 5 g dried and ground foliage can completely annul the suppressive effects of tannins in vitro.…”

“…If microbial activity is hindered, the extent of degradation in the rumen would decline dramatically. As a result, the utilization of crude protein (CP) in forage species by ruminants could be limited by elevated levels of biologically active condensed tannins [5].…”