Effect of monensin on methane and heat productions of steers fed lucerne hay either <i>ad libitum</i> or at the rate of 250 g/hour

Abstract

The effect of monensin supplement (33 mg/kg feed) on methane and heat productions was studied in Brahman steers offered lucerne hay in two feeding regimes: ad libitum (AL) or at the rate of 250 g/h (GPH). The monensin treated animals consumed 65 kg less feed than untreated animals in achieving a mean liveweight gain of.56 kg over 54 days of feeding AL. The 10.5% reduction in daily feed intake due to monensin was associated with a 25.6% reduction in methane production. At equalized feed intakes (adjustments made by covariance) approximately 55% of the reduction in methane caused by monensin was explained by its anorectic effect and 45% by its specific effect on rumen fermentation. In contrast, monensin slightly increased (P = 0.07) liveweight gain, but did not affect methane production in steers fed GPH. Heat production was not significantly altered by the use of monensin in either feeding regime.