Ruminant methane production contributes 34% of New Zealand greenhouse gases, but emissions are affected by feed type. A trial conducted at Dexcel measured methane production by 32 Friesian dairy cows grazing either good quality perennial ryegrass pasture or birdsfoot trefoil (lotus, Lotus corniculatus), a legume with high nutritive value that contains condensed tannins (CT; 2.62 g CT/100 g DM). Half the cows on each diet were drenched with polyethylene glycol (PEG) to inactivate the CT and allow the effect of CT on methane production to be determined. Total methane production, measured using the SF6 tracer technique, was similar for the lotus and ryegrass cows (343.2 vs 360.6 g CH4/cow/d; ns), however, methane production per unit DMI was lower from cows fed lotus (19.9 vs. 24.2 g CH4/kg DM, P<0.001). The CT in lotus reduced methane production by 13% relative to lotus when the CT had been inactivated by PEG, and was responsible for 66% of the difference between lotus and ryegrass. Cows fed lotus produced 32% less methane/kg milksolids compared to good quality ryegrass. The feasibility of feeding lotus as a methane mitigation option should now be assessed at a farm systems level to investigate effects on other greenhouse gases, productivity and profitability.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 160-164, 2004
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