Monensin is an ionophore used to increase the efficiency of feed utilisation when grain-based rations are fed to beef cattle, but it can also lower energy losses to methane. A series of feeding experiments has been undertaken to measure the impact of monensin on methane production by dairy cows fed ryegrass-dominant pastures alone or with white clover, or maize silage. Methane production measured from 15 sets of identical twin cows fed indoors was reduced by 9%, from 16.9 to 15.3 g/kg dry matter (DM; P < 0.01), and remained 10% lower (P < 0.05) than Controls 72 days after the monensin capsule was given. When pasture was substituted with maize silage at 12, 24 and 36% of DM intake, monensin reduced methane (g/kg DM) by 1, 6.5 and 10.5 % respectively (P = 0.05). However, methane emissions were not affected in cows fed pasture with white clover at 15, 30 or 60% of DM intake. Although monensin provides an important opportunity for methane reduction, the data demonstrate a need to understand reasons for variable responses to treatments under differing nutritional regimes. The added benefits of improved feed efficiency and reduced bloat suggest further investigation of monensin for forage fed ruminants is warranted. Keywords: monensin; dairy cows; methane; pasture; white clover; maize silage.

SJ, Van Vugt, GC Waghorn, DA Clark, and SL Woodward

Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 362-366, 2005
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