Methane emissions from the rumen of sheep fed a mixed grass-clover pasture at two fertilisation rates in early and late season

Abstract

In vivo CH 4 production from four rumen-fistulated sheep fed fresh ryegrass-white clover (Lolium perenne – Trifolium repens) diets ad libitum was monitored using C 2 H 6 as a tracer gas. Treatments comprised mixed pastures at two different fertilisation rates (0 vs. 150 kg N ha –1 yr –1 ) and at two periods in the growing season (early, June–July vs. late, August–September). Higher crude protein (CP) [22.5% dry matter (DM)] in late vs. early season (13% DM) was associated with increased importance of protein fermentation, as suggested by higher rumen concentrations of iso-acids [3.7 ± 1.0 vs. 2.4 ± 0.9% total volatile fatty acids (VFA)]. However, rumen CH 4 production (25.8 ± 5.0 L kg –1 DMI) was not affected, probably because of compensatory seasonal changes in the chemical composition of the pasture, su0 as reduced water-soluble carbohydrates (WSC) (13.0 ± 2.6 vs. 4.9 ± 1.4% DM) or increased neutral detergent fibre (NDF) (48.5 ± 6.1 vs. 57.4 ± 4.6% DM). Although clover saponins might have a defaunation and CH 4 inhibitory effect, considerable seasonal or fertiliser-induced changes in clover proportion did not affect rumen protozoal concentrations (8.8 ± 1.6 ×10 5 mL –1 rumen contents, early season), rumen methanogenesis or microbial growth as suggested from urinary excretion of purine derivatives (6.7 ± 1.7 mmol d –1 ). In contrast, however, a clear animal effect was found: on average, one animal produced less CH 4 than the three others (20.3 vs. 27.6 L kg –1 DMI). Key words: Ryegrass, clover, N fertilisation, season, rumen, methane Mbanzamihigo, L., Fievez, V., da Costa Gomez, C., Piattoni, F., Carlier, L. et Demeyer, D. 2002. Les émissions